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Author Topic: What's your kitchen science?  (Read 398057 times)

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
 

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!
 

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!
 

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 »
 

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.

 

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.
 

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.
 

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 »
 

Offline Bass

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What's your kitchen science?
« 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 »
 

paul.fr

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

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.
 

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



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:



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.






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 »
 

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 »
 

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
 

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 !
 

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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« 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!



 

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.


















 

Offline neilep

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« Reply #268 on: 21/05/2008 15:48:33 »
TORNADO IN A JAR

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.
 

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.
 

paul.fr

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What's your kitchen science?
« 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. »
 

paul.fr

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What's your kitchen science?
« 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.
 

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. »
 

Offline techmind

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What's your kitchen science?
« 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 »
 

Offline neilep

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« Reply #274 on: 13/06/2008 23:30:00 »
MAKE LIGHTNING IN YOUR MOUTH


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.
 

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What's your kitchen science?
« Reply #274 on: 13/06/2008 23:30:00 »

 

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