What's your kitchen science?

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paul.fr

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What's your kitchen science?
« Reply #250 on: 10/04/2008 21:24:26 »
The Coriolis effect has been discussed recently on the forum, but what is it and can we visualise it's effect with just a piece of paper, a pencil and a few spare seconds?

What you need


A piece of paper, say A4
A pencil


What you do


Steadily, and carefully, rotate the piece of paper clock or anticlockwise with one hand, and attempt to draw a straight line from one edge of paper to the centre. You may want to mark the centre of your rotation with a small circle to begin with, this will represent one of the poles.


What happens?


Explanation
To begin with, we should know what the wind is and what causes it. The ultimate cause of Earth's winds is solar energy. When sunlight strikes Earth's surface, it heats that surface differently. Surfaces such as snow, sand and soil absorb different amounts of heat. This creates uneven heating of the earths surface, this leads to a difference in air pressure.


As a result we have differences in air pressure (and heat)over the earth, high and low pressure. Very simply, At the equator hot air rises and moves out towards the poles, gradually cooling. It eventually sinks back down to the earth's surface. This cooler air is then forced to flow back to the equator to replace the hot air that is rising. This is wind.

The Coriolis force results in a deflection of air to the right of the direction of the pressure gradient force

Watch this video

Wind Circulation

understanding coriolis

pressure gradient force

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Offline Bass

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What's your kitchen science?
« Reply #251 on: 12/04/2008 21:34:34 »
PANNING FOR GOLD

For anyone interested in panning for heavy minerals (gold, platinum, metallic minerals, iron minerals, and others including rubies, sapphires and garnets)- here is a brief "How to" guide.  Takes a little time and effort.

What you need

gold pan (I recommend green plastic pans with built in riffles)
shovel
waterproof boots and gloves
small jar (to store all the nuggets!)
small magnet wrapped in Saran Wrap

In streambeds, try to dig down to bedrock if possible, or get as deep as possible.  Also look for areas of slack current, such as on the lee sides of boulders.  For beach sands, try to either collect sand that is on bedrock, or find places in the sand where heavy minerals (magnetite, limonite, hematite, illmenite, zircon) collect (a magnet wrapped in Saran Wrap will help you find magnetite if any exists). 

Best to fill the pan about 3/4 full, then in calm water, work the sand/gravel with your hands until you get rid of all the mud/silt (fill the pan with water, work the sediment until muddy, then pour off the muddy water- continue until water stays somewhat clear when stirred up).  The green platic gold pans with riffles built in make this much easier.

Fill with water, then rock the pan gently back and forth while slowly swirling it in a circular motion (this is to get the heavy material to sink to the bottom).  After you've agitated the pan enough to get the heavies to sink, slightly tilt the pan and allow the water with the top layer of light material to wash out.  You can dip the tilted pan into the water several times to allow the top material to wash out.  Fill with water again, swirl and rock the pan, flush out the top layer.  Repeat this until only a small amount of material remains in the bottom of the pan (often this will be mostly black).  You can pick out any obvious non-mineralized pieces of gravel, as these will also sink to the bottom since they are heavier than the sand.  Gently swirl the pan letting the heavy material in the bottom move a few mm at a time, then use a magnifying glass and see if a thin gold line exists at the back (the gold will not move much since it is heavier).  You can remove magnetite (most common black sand residue) with a magnet wrapped in food wrap.

With practice, you can do this in a few minutes- first timers generally take 15-25 minutes.  This is much more enjoyable when the air and water temperatures are warm, otherwise wearing waterproof gloves really helps.

Good luck and have fun!
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paul.fr

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What's your kitchen science?
« Reply #252 on: 21/04/2008 17:04:46 »
What you need


Cotton Wool balls
Pippet or eye dropper
Glass of water


What you do

hold the cotton ball in one hand and the eyedropper in the other. The best way to hold the cotton wool ball is to hold a small portion of the cotton ball between the thumb and index finger.

With the pippet put as many drops of water into the cotton ball as possible. The cotton ball will be full (saturated) when water begins to drip from the bottom. How many drops of water do you think it will take for the cotton wool ball to become saturated?


Explanation

Since no two cotton wool balls are the same, and the drops will all be different, this is what is happening in nature and the formation of clouds. The cotton wool ball represents a white fluffy cumulus cloud.

One inch of rain over one square mile equals 17.4 million gallons of water weighing 143 million pounds (about 72,000 tons). The 'average' cumulus cloud is made up of over 10,000,000,000,000 drops and weighs about 2 billion pounds!

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Offline neilep

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« Reply #253 on: 21/04/2008 18:40:37 »
What You Need:

Two balloons
A Funnel
Water
A Candle
A grown up (if you are a youngie)


What you Do !

Blow one balloon up , secure it and move the candle towards it....it POPS !!!

Fill the second balloon with just a small amount of water..half a cup lets say.
Blow the balloon up...secure it.

Light the candle and slowly move the candle towards the balloon placing the flame where the water is.

What happens ?..or what does not happen ?




Explanation


Don't let the flame heat the bottom of the balloon indefinitely as it WILL burst....but...you should be able to have the flame beneath the balloon for a while. Even to the point where the rubber is gaining a lot of soot from the candle.

Just as the rubber reaches popping temperature , the water inside absorbs the heat and stops it from popping.
« Last Edit: 21/04/2008 18:48:24 by neilep »
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paul.fr

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What's your kitchen science?
« Reply #254 on: 22/04/2008 17:05:05 »
What you need:

Two empty drinks cans
A level surface


What you do:


Lay the two cans parallel to each other, about one inch apart, near the edge of a level surface. Get down to the level of the floor/surface and blow between the two cans.

What happens?

It may take some practice, but the two cans will roll together.

Explanation:

The affect is Bernoulli's principle in action, named after the Dutch/Swiss mathematician/scientist Daniel Bernoulli. By blowing between the two cans, you are making the air between them move faster than the surrounding air. The cans roll together as the higher pressure surrounding the two cans pushes the cans together toward the region of lower pressure.


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paul.fr

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What's your kitchen science?
« Reply #255 on: 23/04/2008 12:58:14 »
What you need


Two, empty two litre bottles (plastic)
hot tap water


What you do


Put two or three cups of hot tap water into each of the bottles, then put your thumb over each bottle opening and shake for about thirty seconds to a minute.

Pour the water out of each bottle and screw the bottle lid on one of the two bottles. Place the two side by side an observe for about 10 minutes.


What happens?


The bottle that had the lid screwed on Should have collapse, yet the other bottle should remain unchanged.


Explanation

The bottle collapsed due to the air cooling inside that bottle. The air cools because the molecules and atoms inside the bottle loose energy as they collide with the bottle side that is exposed to the cooler surrounding air. As their energy decrease so does their velocity and therefore the pressure decreases. Since the pressure inside the bottle decreases, the force of the air outside the bottle begins to crush the bottle.

However the uncapped bottle remains unchanged. As the air cools inside, the drier outside air flows in to take up the space thereby keeping the pressure the same both inside and outside of the bottle.

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paul.fr

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What's your kitchen science?
« Reply #256 on: 28/04/2008 14:52:29 »
What you need


Two table tennis balls / ping pong balls
Hair drier


What you do


Point the nozzle of the hair drier upwards and turn it on to full power, it can be blowing cool air as there is no need for heat. Place one of the balls into the stream of air, and then carefully add the second.


What happens?

Both balls should be suspended by the air, they will occasionally collide with each other making a clicking sound.


Explanation:

Had the balls been raindrops, every time they collided, they would have joined each other, making a larger drop of water.

In rising (cooling) air, water vapor begins to condense on cloud condensation nuclei when the air has cooled to the dew point temperature. As the air continues to rise and cool, water vapor will eventually condense onto the cloud condensation nuclei and form cloud droplets. Since there are many sizes of cloud condensation nuclei in any given air parcel, the cloud droplets that form will be different sizes as well.

As a result of the cloud condensation nuclei size distribution, some cloud droplets will be larger than the rest. Eventually, the largest cloud droplets begin to fall faster than the smaller droplets because large drops have faster terminal velocity than small drops. As these large cloud droplets fall, they collide with the small cloud droplets.

Many times, these droplets will stick together and become one large drop (coalesce). Eventually these droplets fall from the cloud as raindrops, reaching a diameter of approximately 10 mm (0.39 inches). After a raindrop reaches 10 mm, it becomes so large that it breaks up into smaller drops.

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paul.fr

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What's your kitchen science?
« Reply #257 on: 03/05/2008 16:44:52 »
What you need


A freezer
A piece / block of polystyrene


What you do


Pop the polystyrene in to the freezer and leave for 24 hours, take it out.
What has happened?

You should notice that the polystyrene is not frozen and in fact feels warm to the touch!

Explanation:

Hay, don't look at me for an explanation!
Lets throw it open to the forum members.

Link:
Why does polystyrene not freeze?
« Last Edit: 03/05/2008 16:47:15 by paul.fr »

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Offline Bass

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« Reply #258 on: 08/05/2008 05:31:53 »
COSMIC RAY CLOUD CHAMBER

What you need

Wide-mouth Canning jar (1 pint or 450ml size works well)
Metal pan
Felt cloth
glue or double stick tape
pure isopropyl alcohol
dry ice
flashlight

What you do

Cut the felt cloth in a circular shape to fit jar lid
Attach felt cloth to the inside of the jar lid (don't cover the rubber seal)
Pour a small amount of alcohol into the jar (enough to thoroughly wet the cloth plus a little extra)
Seal the jar (a tight seal is necessary)
Place the jar upside down on top of dry ice in the pan
          Remember to wear gloves when handling dry ice

What happens

Due to the temperature difference (warm jar and cold lid), the alcohol will begin to condense and form an alcohol "fog"
As cosmic ray particles travel through the jar, they will ionize particles along their path, causing intense condensation (look for streaks like contrails from jets)
Shining the light at different angles may illuminate the cosmic ray streaks better
Only a thin layer of "fog" will form just above the lid with felt cloth at the bottom.
« Last Edit: 08/05/2008 05:34:44 by Bass »
Old enough to have a grandson
Slow enough to study rocks
Thirsty enough to find a pub

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paul.fr

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What's your kitchen science?
« Reply #259 on: 08/05/2008 14:19:46 »
Excellent, as usual Bass

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paul.fr

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What's your kitchen science?
« Reply #260 on: 08/05/2008 14:19:53 »
What you need


A large, clear plastic bag
rock
A tree


What you do


Place the plastic bag over a limb/branch of the tree (or large bush), making sure that the limb is high enough off the ground so that the added weight of the rock will not make it touch the ground.

Making sure that there are no air leaks or holes, tie the open end of the bag around the tree (or bush). At the closed end of the bag, tie a rock to the bag so the bag is weighted and forms a collection point for the water.

After six hours or so, poke a hole in the bag and collect and measure the water. Then remove the bag from the branch



What happens?


The bag should have some water in it.


Explanation


Transpiration:
There are two methods water moves from the ground to the atmosphere as part of the hydrologic cycle. Transpiration is basically evaporation of water from plant leaves. Studies have revealed that transpiration accounts for about 10% of the the moisture in the atmosphere.

And this is an, easier to swallow, way to get drinking water than drinking your own urine!
But if you must, or want to get someone else to drink their own urine follow the above link.

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paul.fr

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What's your kitchen science?
« Reply #261 on: 13/05/2008 14:47:38 »
What you need

A Barometer
Graph paper pencil


What you do

Draw your bar chart like the pathetic picture below

[attachment=2979]

At regular (say, 2 hourly) intervals over a nember of day plot the reading of your barometer on the graph. After a week you should have something that looks like this:

[attachment=2981]

Explanation

Have you ever seen the "pressure" charts on weather forecasts and wondered what they are and why they are relevant to you and the weather?

Like all fluids, the air exerts a pressure on everything within and around it, although we are not aware of it. Pressure is a force, or weight, exerted on a surface per unit area, and is measured in Pascals (Pa). The pressure exerted by a kilogram mass on a surface equals 9.8 Pa. The pressure exerted by the whole atmosphere on the Earth’s surface is approximately 100,000 Pa. Usually, atmospheric pressure is quoted in millibars (mb). 1 mb is equal to 100 Pa, so standard atmospheric pressure is about 1000mb. In fact, actual values of atmospheric pressure vary from place to place and from hour to hour. At sea level, commonly observed values range between 970 mb and 1040 mb. Because pressure decreases with altitude, pressure observed at various stations must be adjusted to the same level, usually sea level.

Atmospheric pressure is measured by a barometer. A mercury barometer measures the pressure by noting the length of mercury which is supported by the weight of the atmosphere. One centimetre of mercury is equal to 13.33 mb, so normal atmospheric pressure can support a column of mercury about 75 cm (or 30 inches) high. An aneroid barometer is a more compact instrument for measuring pressure. It consists of a box of partially exhausted air which expands and contracts as the pressure falls and rises. The box is connected through a system of levers to a pointer which, in conjunction with a dial, indicates the pressure.

Air blows from regions of high atmosphere pressure ("highs" or anticyclones) to regions of low atmospheric pressure. In a high-pressure system, air pressure is greater than the surrounding areas. This difference in air pressure results in wind, or moving air. In a high-pressure area, air is denser than in areas of lower pressure. The result is that air will move from the high-pressure area to an area of lower density, or lower pressure. Conversely, winds tend to blow into low-pressure areas because air moves from areas of higher pressure into areas of lower pressure. As winds blow into a low, the air can be uplifted. This uplift of air can lead to the development of a depression with clouds and rain.

Air moving from high to low pressure does not however, follow a straight-line path. In fact, the air moving from high to low pressure follows a spiralling route due to the rotation of the Earth beneath the moving air, which causes an apparent deflection of the wind to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere.

[attachment=2983]

[attachment=2985]


After a week, what does you graph show? How was it relevant to the weather you had? Notice any peaks and troughs in your chart, what was the weather like during those periods?


« Last Edit: 13/05/2008 14:50:00 by paul.fr »

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Offline Andrew K Fletcher

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What's your kitchen science?
« Reply #262 on: 15/05/2008 19:45:00 »
A Human Physiology Experiment to show how gravity alters your heart and lung function.

What you need

A bed
Two 15 centimetre blocks or strong plastic tubes (to raise the head end of the bed).  (If your bed joins in the middle then Two 7.5 centimetre blocks to support the join in the middle will also be required)
A stethoscope (Or you can find a pulse with you fingers placed on the inner wrist area)
A clock or watch (to record the time and measure rates against minutes)
A mum or dad   (to monitor your heart rate and respiration rate).
And some serious ZZZZZ’s / sleep

Ask mum to measure your heart rate and respiration rate while sleeping horizontally, taking care not to awaken you and making a note of your breathing and heart rate.

Then the following night tilt the bed by raising the head end 15 centimetres higher than the foot end of the bed.

Ask mum or dad to repeat the same measurements and make a note of them for comparison.

Double cross over:

This is the fun part. All good science is repeatable so we switch the rolls in our simple experiment and you measure your mum and dad’s heart and respiration rate when they are sleeping horizontal and again when they are sleeping on an incline.

If either awakens then you must wait for them to go back to sleep and try again so Shhhh and be quiet as a mouse.

Although this may seem like a simple experiment. This is a very important experiment and your observations will help greatly to improve our knowledge of human physiology and how circulation relates to posture and gravity.

You can also perform the same experiment on your pet dog using pillows to tilt his or her body, but wait until your dog is sleeping.

So please come back and tell us all what you have found in the Nakedscientists forum.
« Last Edit: 16/05/2008 08:42:59 by Andrew K Fletcher »
Science is continually evolving. Nothing is set in stone. Question everything and everyone. Always consider vested interests as a reason for miss-direction. But most of all explore and find answers that you are comfortable with

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paul.fr

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What's your kitchen science?
« Reply #263 on: 20/05/2008 14:06:41 »
What you need

a wooden, cooking skewer
a lighter
3% hydrogen peroxide
a cup or glass
yeast


What you do

Pour some hydrogen peroxide into the glass. Sprinkle some of the yeast into the peroxide and give it a stir. Very quickly you will see bubbles rising, producing foam on top of the liquid.

Light the end of the wooden skewer, and let it burn for a moment. Then blow out the flame. If you blow gently on the burning end, you should see a red glow. It is still burning, but not flaming. Carefully bring the glowing end of the skewer up to the larger bubbles in the foam.


What happens?

The skewer should flare up, bursting into flame.


Explanation

What, you expect me to know why this happens? Best check this topic for answers
http://www.thenakedscientists.com/forum/index.php?topic=14661.new#new

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Offline neilep

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« Reply #264 on: 20/05/2008 14:14:40 »
PAUL.....fantastic thread as always..

...Paul....have you written here how to make clouds in a bottle ?.....I saw it somewhere and can't quite remember it.....I don't want to post it if I am wrong about the implementation of it !
Men are the same as women, just inside out !

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paul.fr

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What's your kitchen science?
« Reply #265 on: 20/05/2008 14:18:36 »
PAUL.....fantastic thread as always..

...Paul....have you written here how to make clouds in a bottle ?.....I saw it somewhere and can't quite remember it.....I don't want to post it if I am wrong about the implementation of it !

Thanks, Neil....Oh, and thanks to Mr Fletcher, i think ;-)
I may have done, but just post it anyway Neil.

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Offline neilep

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« Reply #266 on: 20/05/2008 14:34:11 »
CLOUD IN A BOTTLE 


What You Need


    * 2-liter clear plastic pop bottle
    * matches (children will need adult assistance to light matches)
    * warm water


What You Do


Fill the clear plastic 2-liter bottle one-third full of warm water and place the cap on. As warm water evaporates, it adds water vapor to the air inside the bottle. This is the first ingredient to make a cloud.

Squeeze and release the bottle and observe what happens. You’ll notice that nothing happens. Why? The squeeze represents the warming that occurs in the atmosphere. The release represents the cooling that occurs in the atmosphere. If the inside of the bottle becomes cover with condensation or water droplets, just shake the bottle to get rid of them.

Take the cap off the bottle. Carefully light a match and hold the match near the opening of the bottle.

Then drop the match in the bottle and quickly put on the cap, trapping the smoke inside. Dust, smoke or other particles in the air is the second ingredient to make a cloud.

Once again, slowly squeeze the bottle hard and release.


What happens?

 A cloud appears when you release and disappears when you squeeze. The third ingredient in clouds is a drop in air pressure.

EXPLANATION
:

Water vapor, water in its invisible gaseous state, can be made to condense into the form of small cloud droplets. By adding particles such as the smoke enhances the process of water condensation and by squeezing the bottle causes the air pressure to drop. This creates a cloud!



Men are the same as women, just inside out !

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paul.fr

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What's your kitchen science?
« Reply #267 on: 21/05/2008 01:12:17 »
What you need

plastic lids (jam jar type/size)
petroleum jelly / vasaline
magnifying glass
paper punch
String or cotton
windy day


What you do


Punch a hole at one end of each lid.
Thread each hole with a length of string and knot the ends together to form a loop for hanging.
Spread petroleum jelly over one side of each lid.
Take the lids outdoors on a windy day and hang them in various areas.
Leave them outside for about an hour or two to collect what may be blowing in the wind.
Retrieve the lids and see what they have collected.


what happens?

You may have collected insects, dirt, seeds and leaves. Use the magnifying glass for further observation.

EXPLANATION

The wind collects items as it blows through tree's, grass etc.



















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Offline neilep

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« Reply #268 on: 21/05/2008 15:48:33 »
TORNADO IN A JAR [attachment=3141]

What You Need


    * mayonnaise jar or a canning jar
    * clear liquid soap
    * vinegar
    * water

What You Do

Fill the jar about three-quarters full of water.

Put a teaspoon of the liquid soap into the jar.

Also, add a teaspoon of vinegar into the jar.

Tighten the lid and shake the jar to mix up the ingredients.

Now, swirl the jar in a circular motion.

The liquid will form a small tornado.

*If you want to get creative, you can also use food coloring to make the tornado have a color and glitter to represent debris

EXPLANATION:

The swirling motion you give the bottle forms a vortex and is a easy way to create your own tornado.
Men are the same as women, just inside out !

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paul.fr

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« Reply #269 on: 22/05/2008 19:09:58 »
What you need


a film canister (or similar) filled with soil, with the lid on
two clear plastic glasses
water
two ice cubes
a marker pen.



What you do


Place the film canister upside down into one cup. This represents an island, such as Antarctica. Half fill each glass with water and place one ice cube on top of the ‘island’ and the other ice cube in the water in the second glass.

Mark the level of the water on each glass.

Once both ice cubes have melted, see whether the water level has risen.


Explanation

The ice cube floating in the water has already shifted, or displaced, the water in the glass; so when it melts, the level will barely rise. But the ice cube on the land (film canister) will not displace the water until it melts and drips into it, making the water level rise.

Only the melting of land-based ice and snow (like Antarctica) will increase the sea level. The melting of floating ice (like the North Pole) will not affect the sea level much.

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paul.fr

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« Reply #270 on: 27/05/2008 19:54:43 »
What you need


a tall, clear glass or jar
water
vegetable oil
rubbing alcohol
corn syrup or other sugary syrup
a variety of small objects such as: cork, rubber, plastic, bread, corn flakes, ice, a piece of apple, slice of lemon, slice of lime, etc.
a spoon


What you do


Pour about one and a half inches of corn syrup into the glass. Place the ladle just at the top of the layer of syrup and gently pour in another inch or so of water. The water should form a layer on top of the corn syrup, and by pouring it into the ladle, you keep from mixing the two layers. Keeping the ladle in place, add an inch or so of cooking oil to form the next layer. Once that is settled, add an inch of rubbing alcohol for the top layer. When you finish, place the glass on the table and look at it from the side. You should be able to easily see the different layers of liquid.

The corn syrup is the densest, so it is on the bottom. Next is the water, then the oil, and last is the alcohol, which is the least dense. Now, drop a small piece of bread into the glass. It will float for a second and then as it soaks up the alcohol, it will sink. It does not go all the way to the bottom. Instead, it sinks down to the top of the oil. Soggy bread is denser than the alcohol, but less dense than the oil, so it floats at the boundary of the two.

Drop in raisins, buttons, olives, pieces of plastic, coins, corks, and any other small objects that won't be hurt by putting them into the liquid. Notice which layer each floats on. That tells you their relative density.


Explanation

If an object floats in a liquid then you know its average density is less than the liquid and vice versa.


http://www.thenakedscientists.com/forum/index.php?topic=14732.0;topicseen#quickreply
« Last Edit: 27/05/2008 19:59:25 by Paul. »

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paul.fr

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« Reply #271 on: 01/06/2008 16:21:33 »
What you need

an empty pint-sized milk (or similar) carton
water
two small thermometers
cotton shoelace
string
clear tape


What you do
 
Cut a piece of shoelace 1 inch long and pull it over the bulb of one thermometer, and Tie it in place so it
won’t fall off. Tape the thermometer to one side of the carton and wet the shoelace.

Tape the second thermometer to another side of the carton.

Punch two holes in the top of the carton (the 'lip' area where the expiration date is stamped) and thread a long piece of string through these holes and tie the ends together to form a large loop. You should have something that resembles a box with a long handle.

Go outside and swing the carton overhead while holding onto the string. Do this for one minute. Then Quickly look at the temperatures on the two thermometers and write them down.

What are the temperatures?
Are they different?

Explanation

The temperature of the thermometer with the wet bulb should be lower than the temperature of the thermometer with the dry bulb. This is because water is evaporating from the wet bulb thermometer and cooling it down. The difference between the two temperatures will help you calculate the Relative humidity and dew point.

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paul.fr

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« Reply #272 on: 03/06/2008 16:17:18 »
A member sent this to me...

What you need


Chocolate sauce
Red food dye
Water
Measuring cup
Mixing bowl
Drinking straw
Old clothes
5 large sheets of white paper (at least A3 size)
Scientific calculator


What you do


To make your fake blood, measure 3 parts chocolate sauce to 1 part water into your mixing bowl. Make about one or two cups of mixture then add a dash of red food dye and mix. Add more dye if you feel it is needed.

Lay the sheets of paper in a line, end to end, in an open, outdoor area. You might need to weigh them down so they aren't blown away.

Dip your drinking straw into the fake blood. Gently suck a small amount into the straw, being careful not to drink it (as tempting as it might be!).

Place a thumb over the end of the straw your mouth was on.

With your thumb still in place, stand about 2 to 3 metres away from the end of the line of paper. Starting with your hand down low, remove your thumb and quickly sweep the arm holding the straw in an upward motion. The aim is to flick a line of fake blood out over the paper. It might take some practice to get a nice line of drops you can investigate.

Dip your straw into the fake blood again. This time, walk over to the paper and let one or two drops fall onto it from straight above.

Look at the different drops you made. What shapes are there? Are some drops longer than others? Do some have pointed ends? In which direction do they point?


Explanation


Asked to draw a rain drop, many people draw the typical 'tear' shape with a round lower end and a long tail pointing up. In reality, falling drops of liquid are near perfect spheres.

Blood is no different. A single drop of blood falling straight down descends as a sphere, so it makes sense when it hits a surface it will make a neat circle. However, blood often doesn't fall straight down. If blood is thrown (or 'cast') from a weapon, flicked from a wound, or ejected from an artery by the pressure of a pulse, the drops will often hit a surface at an angle. Rather than round, the drop will be elongated and often have a pointy tail.

As the drop strikes the surface from a steep angle, most of its volume will stick. Inertia carries the rest of the drop forward, often ending in a thin line or tail. Therefore the tail always points away from where the blood drop originated.

Investigators can then use trigonometry to calculate the angle of impact and trace this back to an approximate starting place. Trigonometry is an area of mathematics that describes the relationship between the length of sides and angles in a right-angle triangle. The longer the drop is, the lower the angle will be. It helps to think of the length of a drop as the longest side (hypotenuse) of a right-angled triangle. Since we know the drop started as a sphere, the width of the drop will be the same as its height, giving the second side of the right angled triangle.

The 'sine' of an angle describes the ratio of the angle's opposite side to the hypotenuse. To work out the angle of impact, we measure the drop's width and divide it by its length. The resulting number is the same as the sine of the angle. However, we just want the angle (not the sine of the angle). Most scientific calculators will have a function which looks like 'sin -1 '. This is called its inverse. Use this on your number and it will give you the angle at which the blood hit the surface.


Application


Even if somebody personally witnesses a crime, it can be difficult to know precisely what happened. If somebody is wounded, falling or flying blood can tell investigators where the victim was standing, what type of injury they have, the nature of the weapon used against them and how badly injured they are. By using the angle of impact of a number of blood drops, a person's movements through the crime scene and the actions they performed can often be described.

Trigonometry is used extensively in fields such as forensics, where angles need to be calculated from a few clues. For instance, ballistics experts – who study projectiles like bullets – often use it to trace back from bullet holes to the point of origin.
« Last Edit: 03/06/2008 16:30:47 by Paul. »

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« Reply #273 on: 12/06/2008 23:08:42 »
Experiment with thermal paper

(At Paul's suggestion, I'm re-formatting and posting the experiment originally inspired by and suggested at http://www.thenakedscientists.com/forum/index.php?topic=14879.0 )


The till-receipts from many shops these days, and many bus tickets, are printed on "thermal paper" - much like that traditionally used in FAX machines. The paper is coated with a substance which turns black (strictly dark brown) when it is heated. "Printers" can therefore mark the paper merely by heating it somehow, rather than needing any ink.
Unfortunately for folks hoping to claim on a warrantee, the print has a nasty habit of fading over a period of months!

(copied from previous thread)
I can't help with *why* they fade, but I can clarify that it's primarily the receipts printed on "thermal paper" which do fade. The thermal paper turns black (actually dark brown) when it's heated - but gradually returns to white over many months. This is exactly the same technology that used to be used for faxes... and has become popular for store receipts over the past decade.
The only way to keep permanent copies is to photocopy the receipts soon after you get them.

Kitchen science experiment: hold an (unwanted) receipt or bus ticket somewhere hot** and see it turn black.
** Hot = momentarily against a 25 or 40W lightbulb, in the steam from a kettle, or against a particularly hot household radiator.


I'm fairly sure that an old faded receipt can be blackened again by heating, ie the process reverses - as opposed to a decomposition. If you have an old (and now unwanted) receipt you might try this.

It's interesting that if you hold the receipt in the steam from a kettle (I did more experiments at the weekend) the blackened bit momentarily gets lighter again while in the steam (the hottest part???), but then settles to dark-brown as it cools. The dark/light swirls around a bit with the air/steam flow. It's rather fun to watch.


---------------------------------

Bonus experiment (Oct. 2008), following a random internet tip-off

Apply a piece of Scotch tape to a thermally-printed receipt, and the printing underneath the tape will fade within a few days.
I tested this with genuine Scotch(tm) tape (the slightly cloudy/translucent tape) and verified the tip-off. Tested with Sellotape(tm) (ordinary clear tape) and no such accelerated fading was observed.

You might experiment with different brands/types of sticky-tape and see which work.


---------------------------------


Extra:
If you like thermal experiments, and don't mind spending £16, you might like to buy a thermochromic liquid crystal sheet to play with...
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1642&search=1
(I suggest the 25-30C one is best - but it depends a bit on the ambient temperature in your house/office, you normally want one that starts changing colour just slightly above ambient.)
You can leave a hand-print on a wooden desk and "reveal" it several seconds later with the sheet :-)
Rest the sheet against you computer-screen or other widgets to "see" the hotspots.
Check the product warning though, and don't heat these sheets above 60 degrees Celcius or so.

Not quite as much fun as a £15000 FLIR camera, but much more affordable!
« Last Edit: 28/10/2008 00:02:50 by techmind »
"It has been said that the primary function of schools is to impart enough facts to make children stop asking questions. Some, with whom the schools do not succeed, become scientists." - Schmidt-Nielsen "Memoirs of a curious scientist"

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« Reply #274 on: 13/06/2008 23:30:00 »
MAKE LIGHTNING IN YOUR MOUTH [attachment=3262]


What Ewe Need:

    * Wint-O-Green or Pep-O-Mint lifesavers
    * dark room
    * mirror

What Ewe Do:


Go to a really dark room and stand in front of the mirror. Wait a few minutes until your eyes get accustomed to the darkness.

Put a Wint-O-Green or a Pep-O-Mint lifesaver in your mouth.

While keeping your mouth open, break the lifesaver up with your teeth and look for sparks. If ewe do it right, ewe should see bluish flashes of light.

EXPLANATION:


Why does this happen? When ewe break the lifesaver apart, you’re breaking apart sugars inside the candy. The sugars release little electrical charges in the air. These charges attract the oppositely charged nitrogen in the air. When the two meet, they react in a tiny spark that ewe can see.
Men are the same as women, just inside out !

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« Reply #275 on: 14/06/2008 06:28:51 »
That sounds like the same principal as the sugar cube experiment...Is it?? Kind of cool cause its in your mouth though!

"Life is not measured by the number of Breaths we take, but by the moments that take our breath away."

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« Reply #276 on: 15/06/2008 15:42:21 »
That sounds like the same principal as the sugar cube experiment...Is it?? Kind of cool cause its in your mouth though!

Why don't you post it karen, then we can see.

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« Reply #277 on: 17/06/2008 08:42:05 »
I do believe it was your experiment from the start of this thread... The one where you go into a very dark room with sugar cubes and a pair of pliers. You wait for I think you said two minutes and then your eyes have adjusted to the light.. then you begin breaking the sugar cubes with the pliers.. I believe this is the one we sent home with the kids who were afraid to stay in the dark to see it. We hoped they would be less scared to do it with their folks! LOL

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« Reply #278 on: 18/06/2008 16:57:08 »
Karen, you are correct but i don't think i did that one, i think it was done by Dave on the show with a pair of plyers. Then again i do not have the memory of a goldfish!

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« Reply #279 on: 18/06/2008 16:58:37 »
What you need

Two (glass) milk bottles
matches or lighter
a piece of thick cord or shoe lace a few inches long


What you do

Put one of the milk bottles in the fridge for 10 minutes or so and the other bottle in a pan of very hot water.
After the time is up, Take the cord, light one end and drop it in to the cold bottle. Now turn the warm bottle upside down and place it on top of the cold bottle. Both bottles should have their open end joining.

What happens?

Now turn the bottles upside down.

What happens?


Explanation

First off, the smoke from the lit cord should have remained in the cold (bottom) bottle. When you turned the bottles upside down the smoke should have dropped in to the bottom bottle, but why?

In the first instance the smoke is held down by the heavy cold air, then when you turn the bottles upside down the cold and heavier air drops down in to the bottom bottle and again keeps the smoke there. The warm air is push up in to the top bottle because warm air is lighter.

Please use caution around matches and hot water.

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« Reply #280 on: 19/06/2008 18:34:04 »
Karen, you are correct but i don't think i did that one, i think it was done by Dave on the show with a pair of plyers. Then again i do not have the memory of a goldfish!

Thanks Paul.. I know I got it off here!LOL

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« Reply #281 on: 20/06/2008 12:04:16 »
Here is a slime recipe we have used at the preschool. We got it from the internet way back.. but I do not have the site..(Sorry) Its fun stuff Kids and adults alike like it! try the options they are cool too!

Try this one:

SLIME RECIPE

1/4 cup White Glue
1 1/4 cup Water, divided
1 tbsp. Borax - found in the laundry detergent aisle of your grocery store
Food Coloring

Borax is available in the laundry section of your local grocery store. Add 1 tbsp. Borax to one cup of warm water. Stir until completely dissolved.

Make a 50% water 50% white glue solution. Take 1/4 cup of each and mix thoroughly.

In a ziploc bag, add equal parts of the borax solution to equal parts of the glue solution. (Half cup of each will make a cup of slime.)

Add a couple drops of food coloring. Seal bag and knead the mixture.

If slime is too sticky, add a little more borax. If slime is too slippery, add a little more white glue solution.

Variations:

Less rubbery & more transparent slime: Try a 4% solution of polyvinyl alcohol instead of the glue mixture.

Different Consistencies: Add shaving cream or baby powder to the mixture

Glow in the Dark Slime: Add several drops of glow-in-the-dark paint during mixing.




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« Reply #282 on: 23/06/2008 09:13:16 »
What you need

Cloth bag or a non-transparent container
Marker pen
Notepad
Calculator (optional)
Template of ‘Forty Fine Fish'
Coloured card or paper
Scissors
A friend

What you do

Draw and cut out 'Forty Fine Fish', preferably on coloured card.

Ask your friend to secretly count out a number of fish tokens and place them into the container or bag. To make it more of a challenge, ask them to make it any number higher than 20.

Now it's time to go fishing. To get an estimate of the number of fish, you need to do several fishing trips:

    * On your first trip, pull ten fish out of the container and 'tag' them with a cross using your marker pen before returning them
    * On your second trip, shake the container then pull out another ten fish without looking. Count how many of those fish are marked with the cross and write down the number, then return them to the container and mix them up
    * Now go fishing a third time, again recording the number of fish with crosses and returning them to the bag, mixing again
    * Go fishing one last time, writing down the number of fish you catch with crosses.

Add these 3 numbers and divide the result by 3 to get an average result. For example, if you counted 5 with crosses, then 3, and then 4, this equals 12. 12 divided by 3 equals 4.

The equation which estimates the total number of fish in the bag is:

    (Total number caught the first time x total number caught the second time) / average number caught with a cross

In our example, this would be (10 x 10) / 4. This equals 25, which is our total estimate.

Ask your friend for the actual number. Is your estimate close?


What's happening?

Estimates are guesses based on a small amount of information. Obviously we can't know the exact number of fish in a large area like a lake, so we need some way of getting a small amount of information and then making a guess based on it.

When you go fishing, you are taking a ‘sample' of the larger population. Samples usually represent the population you want to know more about. For example, half of a school might be boys and half girls. If you took a sample of the school, such as one class of students, it should also have about half boys and half girls. If you wanted your estimate to be more accurate, you could count two classes instead to get more numbers.

Your first fishing trip took one sample, and then tagged them all as caught. The second fishing trip counted the same number you caught the first time and compared it with the number of new (untagged) fish being caught. Obviously, if there aren't a lot of fish, you'll catch most of them again. But if there are large numbers of fish in the lake, you mightn't catch any tagged fish at all the second time.

Mark-and-recapture, also called tag-and-release, is a way of using samples to estimate the size of a population when you can't possibly count them all any other way.


Applications

Many organisms don't sit still long enough to be counted. People aren't all that different –it's difficult to study all of the people in a large area, which is why we do surveys. This means we study a small 'sample' part of a large number of people to provide us with an example of what other people might do as well.

We must be careful that our sample is similar to the whole population we want to study. Would it be accurate to study what breakfast cereal most people prefer if we only asked toddlers? Or what television shows all ages watch by only asking parents? Such is the case with our fish – it is only accurate if we can catch all types of fish we want to count. Imagine catching the fish using a net with holes big enough to let smaller fish through. Would this give us an accurate estimate?

"borrowed" from CSIRO.
either cut your own fish shapes out or use this template:
http://www.csiro.au/helix/sciencemail/activities/images/FortyFineFish.pdf
« Last Edit: 23/06/2008 09:31:15 by Paul. »

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« Reply #283 on: 25/06/2008 19:28:54 »
What you need   


2 short glasses of water
A pie plate or tray
Liquid dish soap


What To Do

Put the first glass of water in the center of the pie plate, then slowly pour some water from the second glass into the first glass until it is very full and the water forms a dome above the rim of the first glass. Set the glass with less water aside.

Carefully stick your finger straight down through the dome of the water in the full glass and watch what happens.
Then put a small drop of dish soap on the tip of your finger and do the exact same thing - stick the finger with soap on it straight down through the dome of water.

what happens this time?


Explanation

Water is made up of lots of tiny molecules. The molecules are attracted to each other and stick together. The molecules on the very top of the water stick together very closely to make a force called surface tension. Surface tension is what caused the water to rise up above the rim of the glass in the experiment - the water molecules stuck together to make a dome instead of spilling over the side. Why didn't the dome break when you stuck your finger through it? Why didn't the water spill over the glass? Well, the surface tension was strong enough that it just went around your finger. The water molecules still stuck to each other and nothing spilled! What happened when you put your soapy finger into the water? The soap on your finger broke the water's surface tension and some of the water molecules didn't stick to each other any more and they were pushed out of the glass!

The force of surface tension also creates bubbles. In plain water, the surface tension is strong and the water might make some bubbles, but they will not last very long and they will be very small, because the other molecules in the water will pull on the bubbles and flatten them. Soap needs to be mixed with the water to make bubbles that can float through the air. When you add soap, the water becomes flexible, sort of like elastic, and it can hold the shape of a bubble when air is blown into it.

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« Reply #284 on: 26/06/2008 09:21:02 »
What You Need

Liquid dish soap
Distilled water (tap water is okay, but distilled water makes the best bubbles)
2 clean containers with lids
glycerin or light corn syrup
Measuring cup
Mixing spoon
A plastic pipet (cut off the closed end to make a bubble blower) or a drinking straw
Tape and a marker


What you Do



Homemade bubble blowerMeasure 6 cups of water into one container, then pour 1 cup of dish soap into the water and slowly stir it until the soap is mixed in. Try not to let foam or bubbles form while you stir.
Once the soap and water are mixed, go outside to test it. Dip the cut end of your bubble blower into the solution and let the extra drip off. Blow through the narrow end to make bubbles. Do you get a lot of bubbles? How big are they? How long do they last before they pop?

pour half of the bubble solution into the other container. Put a piece of tape on the outside of the new container. Use the marker to label it "Super Bubbles."
Measure 1 tablespoon of glycerin or 1/4 cup of corn syrup and add it to the "Super Bubbles" container. Stir the solution until it is mixed together.
Dip your blower or straw into the new bubble solution and blow. Are these bubbles different from the plain soap and water bubbles? Are they bigger or smaller? Do they last longer or pop faster? Can you blow a really big bubble?

To make even better bubbles, put the lid on the container and let your super bubble solution sit overnight. You can add glycerin or corn syrup to the other container to make those bubbles better, too. (Note: If you used "Ultra" dish soap, double the amount of glycerin or corn syrup.).


Explanation

The first bubble solution was just soap and water. As you learned from the Surface Tension experiment (above), soap helps bubbles form. You probably got some small bubbles that didn't last very long from the soap and water. Then you added glycerin or corn syrup to the soap and water and probably noticed that the bubbles you blew were stronger and better than before. Did they last longer? Were they bigger? The glycerin or corn syrup mixes with the soap to make it thicker. When the water that is trapped between the layers of soap in a bubble evaporates (or dries up), the bubble will pop! The thicker skin of the glycerin bubble keeps the water from evaporating as quickly. You can probably also blow a much bigger bubble with the second bubble solution that you made than with the plain soap and water one. Adding glycerin or corn syrup makes bubbles stronger and helps them last longer. It makes super bubbles! 

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« Reply #285 on: 27/06/2008 14:04:49 »
What you need


the above bubble solution
the lid from the container
a straw
some objects with pointed ends.



What you do


Set the lid on the table so that the part with the lip is facing up. Fill the lid with bubble solution. Dip your straw into the bubble solution container so that it is wet half way up the straw. Touch the straw to the
lid and blow a bubble on the lid. Slowly pull the straw all the way out of the bubble.

Now dip the pointed end of your scissors (or any pointy object) into the container of bubble solution. Make sure they are completely wet. Poke the scissors through the wall of your bubble. Watch what happens. Try it again with other pointed objects, just make sure anything you touch to the bubble is wet. Can you stick your finger through the bubble?



What's Happening?


Stick an object through a bubble!You should have been able to push the scissors through the wall of the bubble without popping it! When something wet touches a bubble, it doesn't poke a hole in the wall of the bubble, it just slides through and the bubble forms right around it. The bubble solution on the scissors filled in the hole that would have been made. If you try poking dry scissors through your bubble, you will see it pop instantly! (If it popped when you put the wet scissors in, something was probably too dry. Try it again and make sure anything that touches the bubble is completely wet with bubble solution.) For another trick, get one hand completely wet in the bubble solution then use the other hand to hold your bubble blower and blow a big bubble in the palm of your wet hand.

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« Reply #286 on: 28/06/2008 01:20:00 »
If you take two sheets of clear glass or plastic separated by about one-half inch, soak them in soapy solution and then blow bubbles between the sheets, you will get many bubble walls. If you look closely, you will notice that all of the vertices where three bubble walls meet (and there are always three,) form 120 degree angles. If your bubbles are of uniform size, you will notice that the cells form hexagons and start to look much like the cells of a beehive. Bees, like bubbles, try to be as efficient as possible when making the comb. They want to use the minimum possible amount of wax to get the job done. Hexagonal cells are the ticket.

[attachment=3490]

When one bubble meets with another, the resulting union is always one of total sharing and compromise. Since bubbles always try to minimize surface area two bubbles will merge to share a common wall. If the bubbles are the same size as the bubbles to the left, this wall will be flat. If the bubbles are different sized, the smaller bubble, which always has a higher internal pressure, will bulge into the larger bubble.

[attachment=3489]

Regardless of their relative sizes, the bubbles will meet the common wall at an angle of 120 degrees. All three bubbles meet at the center at an angle of 120 degrees. Although the mathematics to prove this are beyond me, the 120 degree rule always holds, even with complex bubble collections like a foam

[attachment=3488]

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« Reply #287 on: 28/06/2008 01:33:19 »
some bubble facts.

What Are Bubbles?

Bubbles are pockets of soap and water that are filled with air. When soap and water are mixed together and air is blown into the mixture, the soap forms a thin skin or wall and traps the air, creating a bubble. Soap bubbles are not the only kind of bubbles. You can find bubbles in lots of liquids. You might see small bubbles in plain water, but they will always be in the water, or floating on the surface of the water, not floating through the air. There are bubbles in soda pop, too. The special thing about soap bubbles is that they can float freely in the air; they don't have to be touching water or another liquid like most bubbles do. Can you find other bubbles around your house? What about something that is round and filled with air like a bubble? (Some examples are balls, balloons, and bubble wrap.)

How does soap help make bubbles out of water? Soap makes the surface tension of water weaker than normal. It also forms a very thin skin that is more flexible than water. When air gets trapped under the surface of the mixture of soap and water, the flexible skin stretches into a sphere shape (round like a ball), making a bubble! You can see the flexible skin that forms a bubble by dipping a bubble wand into some bubble solution. When you pull it out, the hole will be filled with a stretchable skin of liquid. If you blow gently on the skin, you'll blow a bubble!

What Happens to Bubbles?

Since bubbles are made from soap and water, they can only last as long as the water lasts. In dry air, water evaporates - it is soaked up by the dry air around the bubble and the skin of the bubble gets thinner and thinner until it finally pops! Evaporation isn't the only thing that pops bubbles. Anything dry can pop them. When a bubble floats through the air and lands on your finger, on a blade of dry grass, the wall of your house, or your pet's fur, the bubble will pop. When something sharp and dry touches the bubble, it pokes a hole in the bubble's skin, all the air goes out of it, and the bubble disappears! To learn how to touch a bubble without popping it, do Trick 2 in the Bubble Tricks experiment.

Why Are Bubbles Round?

Bubbles that float in the air and are not attached to anything are always round because the thin wall of soap is pulling in while the air inside of it is pushing out. A bubble always tries to take up the smallest amount of space and hold the most air that it possibly can. A sphere, the round ball-shape of a bubble, is the best way to take up a little space and hold a lot of air. Even when a bubble starts out as a square or another shape, like in Trick 1 from the Bubble Tricks experiment, it will always turn into a round sphere as soon as it floats away into the air. A square bubble would take up more space than a round one.

Lots of bubblesThere are a few times when bubbles are not round. Sometimes the wind blows them into different shapes. When bubbles are surrounded by lots of other bubbles, the ones in the middle get squished into other shapes, like squares or hexagons (shapes with six sides). Try blowing a lot of bubbles right next to each other in a shallow container and see if there are any that are not round. If you pop the bubbles on the outside, the ones on the inside will not be squished anymore and they will push back out to round bubbles again!

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« Reply #288 on: 30/06/2008 09:01:53 »
Comments welcomed.
http://www.youtube.com/watch?v=187awfsgHoY Video

What You Need:

2 litres of water 2 kilos of granulated sugar, large saucepan and supervision is a must because boiling anything on a cooker is dangerous and boiling syrup will cause severe burns if it comes in contact with the skin.

Scale down to 1 k of sugar and 1 litre of water in a smaller pan.

Add water and all of the sugar to the saucepan and begin to heat it.

Observe closely how the denser fluid at the bottom of the pan behaves as the heat begins to motivate the syrup. At the same time observe the vapour bubbles and the rapidly agitating syrup below the surface.

Adding heat to the water and sugar crystals accelerates the dissolving of the sugar creating a very dense solution. The surface of the syrup does not boil, yet below the surface about half way down the saucepan is clearly boiling and if you look very close you can see lots of large and small gas bubbles forming and rising as you would expect them to do. However if you study what is happening you will see that the surface of the syrup remains unbroken and shows little if any motion while below the surface it is completely different and actively bubbling and boiling.

So what do you think is happening?

I suspect that a flow and return circulation is operating in the lower active level of the syrup where the heat is causing the fluid to form gas and rise but in doing so is generating a return flow from the cooler water causing the rotation of the syrup rather than it reaching the surface and disrupting the stagnant state. The dense syrup is acted upon by gravity and the heat at the base of the pan changes the density of the syrup causing it to rise, where it meets the lower part of the cooler surface less dense syrup and returns back to the base of the pan taking with it the vapour bubbles and preventing them from reaching the surface of the liquid.

Before all of the sugar has turned into clear liquid stir the solution with a wooden spoon and let it return back to the un-agitated state and you should see the lower level behave as before and the surface layer remain once again still.

Eventually the surface syrup heats up and the liquid boils as one would expect a liquid to boil. Yet when another Kilo of sugar is added to the now boiling syrup the same low surface flow happens again and the surface of the liquid stagnates until all the sugar has dissolved and the liquid is boiling in the normal manor.

This is a fascinating experiment that requires supervision as boiling syrup is very dangerous. The sugar looks like clouds viewed from an aircraft for a while.

What does it tell us?

Having been working on a density flow theory in plants, trees, animals and humans that generates circulation by density changes occurring in the fluids due to evaporation, the boiling syrup experiment shows how powerful this gravity driven flow really is. It also shows how density changes at the surface of the ocean due to evaporation and the resulting increases in density of surface water generate an underwater river that drives the Atlantic Conveyor system, a river thought to be larger than all of the combined rivers in the world that powers the world’s weather.

But does it also tell us something about the nature of gravity?

Andrew K Fletcher

You may also be interested in my other density videos on You Tube and if you like them please leave a comment and rate them :)
Science is continually evolving. Nothing is set in stone. Question everything and everyone. Always consider vested interests as a reason for miss-direction. But most of all explore and find answers that you are comfortable with

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« Reply #289 on: 03/07/2008 16:41:18 »
What you need


a key
a saucer or plastic bowl large enough to contain the silver object
a cardboard box large enough to cover the silver object
Something made of silver or something silver plated.  It should be something that is easy to polish, as you will have to polish it twice.  Flat surfaces work much better, so a spoon or knife will work very well. The experiment will not damage the silver, but I suggest that you avoid ornate pieces with lots of hard to polish areas.
Tincture of Iodine (with the medical supplies at your local store) 


What you do


Polish the silver until it is very shiny.  In a dimly lighted area, place the silver object on a saucer or in a plastic bowl.  Carefully pour some iodine over the silver and then cover it with a box, to keep out as much light as possible.  Wait for about two minutes.

Remove the cover and shine a very bright light, such as a bright lamp onto the silver.  Hold the light there for about four minutes.  Then remove the bright light and rinse the iodine from the key and the silver.  Remove the key and look at the surface of the silver.  You will see the image of the key.

Polishing will remove the resultant tarnish from the silver, with no harm done.


Explanation:


The iodine reacted with the silver to form a chemical called silver iodide.  Silver iodide is sensitive to light.  In bright light, it change into silver oxide, a dark colored chemical.  That reaction does not happen under the key, where the light does not reach, so that part of the silve stays light colored.  Together, this produces a negative image of the key.

This is basically the same thing that happens in a photograph.  The parts of the film that are hit by light are changed, while the parts that remain in the dark are not.  This produces a negative image.  Shining a light through the negative onto treated paper gives you a negative image of the negative, in other words a positive image.

Warning!  Iodine is toxic and will stain skin and clothing.

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Offline neilep

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« Reply #290 on: 03/07/2008 18:19:42 »
BEND WATER [attachment=3555]

What You Need:
(go on...go and get this...beware..some combs bite !)

    * comb
    * a piece of wool, nylon or fur

What you do:....do it....do it now !!

Rub a comb quickly against the piece of wool, nylon or fur for about a minute

Hold the comb near a trickle of water from a faucet.

What Should happen:

The charged comb should attract the water toward it.



Why does this happen?
(I'll tell ya shall I ?...yes..yes I will !)

 By rubbing the comb, you’re covering it with little negative charges. The negative charges are attracted to the positive charges against the water.




Warning: Water may inadvertently splash on ewe...and if ewe're like me..(who bathes just once a year)...then you must be warned that a part of you may accidentally become clean !!
« Last Edit: 03/07/2008 18:22:00 by neilep »
Men are the same as women, just inside out !

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paul.fr

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What's your kitchen science?
« Reply #291 on: 04/07/2008 22:54:08 »
What you need


Portable ultraviolet light
Bottle of tonic water (unopened)
Drinking glass, clear
Darkened room


What you do


Open the tonic water and pour some into a large, clear drinking glass. Place a white sheet or poster board behind the glass to create a white background. Turn off all the lights and completely darken the room. Turn on the black light and shine it on the tonic water.

what happened?


Explanation

The black light gives off UV light which is a higher energy light than visible light and the human eye is not able to see it well. So, if ultraviolet light is virtually invisible, how can the tonic water glow so brightly? The tonic water's color under the UV black light is fluorescent-blue because it contains quinine, a substance that changes when it absorbs UV light. When the black light shines on the tonic water, the tonic water absorbs the light and excites the electrons. Since the electrons naturally want to return to their original relaxed state, they give off energy that has a wavelength in the blue part of the visible spectrum. That's why the tonic water has an eerie blue glow in the presence of ultraviolet light!

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Anastasia.fr.1

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« Reply #292 on: 05/07/2008 18:59:27 »
What you need

A piece of paper
A pencil
A drinking glass.
A jug of water.


What you do


Fold the sheet of paper in half and draw an arrow in the middle of one side.

Stand the folded paper on a table with the arrow pointing left. place the empty glass in frount of it. now fill the glass with water. now slowly move the piece of paper away from the glass, you should be looking though the glass as you do this.

what happens to the arrow [?] [?] [?]

I dont know why this happens but grahem does [8D]
 http://www.thenakedscientists.com/forum/index.php?topic=15658.0

By  Anastasia-marie

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Anastasia.fr.1

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« Reply #293 on: 05/07/2008 20:57:43 »
It's not a science experiment, but it's fun to do.

think of a number 1-10
double it
add 14
divide by 2
take away the first number you thought of

i bet your left with the number 7

MAGIC MAGIC
by Anastasia

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Anastasia.fr.1

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« Reply #294 on: 06/07/2008 10:32:17 »
You will need


Template
Photocopier (optional)
Large sheet of card – the bigger the better
Cutting blade or scissors
Ruler
Coloured card, pens and pencils
Glue and/or sticky tape


What to do
Download this Template
 and print it out.

The bigger the model is, the better the illusion works. There are two ways you can make the template bigger if you wish:

Use a photocopier to blow the image up onto one or more sheets of A3 paper.
Measure the lines on the template and multiply them all by the same number to come up with a larger scale diagram. Use a protractor to measure the angles of each part of the template. Use a ruler to draw this new template onto your card.
Cut out the template, then trace it onto the card.

Notice that one panel is decorated with a distorted chequered pattern – use pens or coloured card to copy this pattern as precisely as possible, or better yet, cut the pattern out of the template paper and glue it in place onto the card.

Decorate the rest of the panels as if it is a room, paying attention to how one end of each panel is narrower than the other end. So, if you draw a window or a picture, it must also have one end narrower than the other.

Cut the model out of the card. Remember to also cut out the two shapes labelled ‘x’; one is so you can reach into the model, and the smaller hole is for you to look into the model.

Fold the model into a box shape and glue or tape the tabs in place on the outside.

Take two small objects roughly the same size (e.g. two toy cars) and place one in each corner of the box opposite the small hole.

Peek through the hole. How do the objects look?

What’s happening?


This model is called an ‘Ames room’, named after the ophthalmologist Adelbert Ames who first created one. If the model is neat enough, the room should look fairly normal when peering through the hole. One of the objects should look smaller than the other, however, even though they are the same size.

We use a number of clues in our visual field to determine the size of an object. For example, the slightly different positions of our two eyes on the front of our heads mean each eye sees a slightly different picture. Combined, these two images give objects depth, but can also give clues about how far away they are.

A more important clue, however, comes from the assumptions our brain makes about the room. It is difficult for your brain to tell whether the far wall is perpendicular (at right angles) to your line of sight, or slanted away. However, there is a rule your brain is familiar with – two straight lines coming together to a point indicates distance. Think about how the parallel lines of a railway track seem to converge in the distance.

Using that rule, your brain determines the room is ‘normal’, which means both objects are the same distance away when they really aren’t. The conclusion it comes to? One object is actually smaller and close by rather than far off in the distance.

Applications


Ever wondered how Gandalf was made to look so much bigger than the hobbits in The Lord of the Rings? No, they’re not using shorter or taller actors – they are all roughly the same height in real life. While computer effects could be used, this can be expensive.

A cheaper method for film makers is to use effects such as those used in the Ames room to make things seem bigger or smaller. While the set looks normal on film, in real life it has been built using odd angles. When one actor stands on one side of the room with another actor opposite them, they look as if they are standing side-by-side, where really one is standing further in the distance, making them look small.

written by CSIRO.


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paul.fr

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« Reply #295 on: 10/07/2008 14:20:07 »
What you need


a pie pan or shallow bowl
a candle
a glass jar large enough to hold the lit candle
water

 
What you do


Light the candle and let a few drops of melted wax fall on the middle of the pan.  Place the bottom of the candle into this wax to secure it in place.  Carefully add about an inch of water to the pan.  Relight the candle if it has gone out, and place the jar over it.  Watch carefully.  After a minute or so, the candle will go out, and the water will rise up into the jar.

 
Explanation

This shows that the candle has burned up the oxygen, and the water has risen into the jar to take its place, right?  WRONG!!!!!   If you watch carefully, you will see why is it wrong.  When you first place the jar over the candle, air bubbles OUT of the jar.  If you are slow about placing the jar over the candle, you might not notice this, but if you cover the candle in one quick motion, you will see the air bubbling out.   Once the candle goes out, the water begins to rise in jar. 

 
Now, lets think about that.  If the water was rising because the oxygen was burned up, it would rise while the candle was burning and stop as soon as the flame went out.  Is that what you saw?  No.  Then what really did happen?

 
As the candle burns, it is heating the air in the jar, causing it to expand.  This causes the bubbles that leave the jar.  The candle is burning oxygen, but the oxygen does not vanish.  It combines with carbon from the burning wax to form carbon dioxide, another gas that also takes up space. 

 
When the candle goes out, the air begins to cool, which causes it to contract.  As the air gets smaller, the water rises into the jar. 

Written by Robert Krampf
 


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paul.fr

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What's your kitchen science?
« Reply #296 on: 20/07/2008 15:55:23 »
What you need


Tap water
A glass or clear beaker


What you do

Fill the glass with tap water and put it somewhere it will not be disturbed, go to bed and examine the glass in the morning.
What happened?


Explanation:

You should have noticed that the water in the glass had bubbles, the bubbles should be on the side of the glass. But how did the bubbles get in to still tap water?
Well I have no idea, but luckilly for us, Ian does know.
Where did the bubbles come from in my glass of water?

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paul.fr

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« Reply #297 on: 23/07/2008 15:42:59 »
What You need


A4 sheet of paper
Scissors
Sticky tape


What you do


Fold the A4 paper lengthways into thirds. Use the creases to neatly cut one-third of the sheet away. You will be left with a sheet that is now two-thirds the original size and creased into halves.

Take one of the long edges of the sheet and make a fold about 1 cm wide. Run a fingernail along the crease to press it down firmly.

Repeat this process, folding the edge over four or five times, until you reach the middle crease.

Turn the sheet over and grip the shorter ends of the sheet, with one end in each hand. Find the edge of a desk or the back of a chair, and rub the folded side of the sheet back and forth over the edge. After a few rubs, you’ll notice the sheet will start to curl.

Continue to roll the sheet into a circle, tucking one edge into the fold of the other. Use sticky tape to secure the edges into place.

To throw: pick up the tube as if it is a can of soft drink, with the folded side at the bottom. Find a large, open space and aim the folded side of the tube in the direction you want the tube to fly. Swing your arm back and throw it.

Do it again, this time remembering to spin it with your fingers as you release it.

With practice, your paper ring should fly quite a long distance.

Explanation:


The paper ring flies for much the same reason a normal paper plane does.

Many forces come into play – thrust (propelling the plane forward) is opposed by drag (the resistance of the paper against the surrounding air). Throwing the ring gives it thrust.

There is also gravity pulling the plane’s mass down. But, the ring doesn’t fall because the shape of the wing is special – as air flows close to the surface, some of it is slowed down by the resistance against the wing. As this happens differently on the outside than it does on the inside, it creates a difference in how the air pushes against the paper on each side. This is called ‘lift’, and helps increase the force under the ring which keeps it from falling due to gravity…at least until the thrust runs out.

One reason the ring eventually falls is because of its unstable flight path. The ring will naturally want twist away from where you throw it, which takes away some of its thrust. By spinning it, you give the paper ‘angular momentum’. It acts like a gyroscope, making it more stable as it flies and allowing it to get more out of the thrust.

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Offline neilep

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« Reply #298 on: 08/09/2008 20:29:31 »
Posted this as a genuine question but it also serves as a contribution to the FANTASTIC thread !

Dear Peeps Who Sing This !

"Roll me over lay me down and do it again
Roll me over in the clover, roll me over lay me down and do it again"


As a sheepy, I of course indulge in consuming fizzy drinks !


See my fizzy can of pop ?

[attachment=4463]

Hmmm...what delicious treat resides inside I wonder ?

Now then, If I take another one....shake it hard and then place both of them at the top of a slight incline...the shaken one will roll down slower !!


Why's that then ? Why does the non shaken one roll faster ?


I don't know.. I simply do not have a freaking clue !!

Oh how I wish I knew !...will someone who knows this tell me ?

Thanks

Hugs and shmishes


Neil
Soda Pop Problem Asker

xxxxxxxxxxxxxxxxxxxxxxxxxxxx

mwah mwah mwah mwah !!!
Men are the same as women, just inside out !

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Offline Cameron Lapworth

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« Reply #299 on: 09/09/2008 01:38:21 »
Hi,
   Another one I've done with my year 8's in science is building an electric motor with a magnet battery and some cardboard and a coil of wire. very impressive you can really get some speed up.  I've found a link to something similar  here.  try it it's great.  newbielink:http://www.pbs.org/weta/roughscience/discover/powerplant.html#motor [nonactive]

Cameron