[Bass]

Everyone is fascinated with volcanos- and almost all of us have seen the model volcanos erupting with vinegar-baking soda-food coloring.
For different type of volcano model that shows how craters (calderas) form here's an easy demonstration:

Get a box, at least 2 feet (65 cm) square, and seal the inside bottom with tape (otherwise you end up with flour on the floor).  Punch a small hole in the bottom, and stick a bit of tubing through the hole.  Attach the tubing inside the box to a small ballon (rubber bands work well).  Inflate the balloon, then build a mountain of flour (or some other fine grained material) on top of and around the balloon (but all contained in the box).  Slowly release the air from the balloon, and the collapse crater will form on the top of the flour "mountain".  Varying the rate of balloon deflation will change the pattern of the crater.
Another suggestion was to use different colored layers of flour to better demonstrate what happens during collapse.

[paul.fr]

Excellent. Thanks for the contribution, Bass.

[paul.fr]

what you need

a balloon
a hexagonal nut without any sharp edges


what you do

pop the nut into the balloon and inflate it, tie the balloon off, and whilst holding it move the balloon in such a way that the nut rolls around inside.

do not hold the balloon tight in both hands, just a light grip from two fingers off each hand will do.

what happens?

[paul.fr]

what you need

a candle that's the same width all the way down
matches
two glasses that are the same height
a darning needle
a knife
a room without a breeze
an adult to help you with the knife, the needle & the matches

what you do

cut the bottom 1cm off the candle so the wick is exposed, and poke the darning needle through the middle of the candle (the closer to the middle you are, the better it'll work).
put your two glasses upside down and balance the ends of the needle on them, so the candle can swing through between them.
make sure the candle is balanced, and then light one end and then the other.

wait...what happens?

with a knife and matches used in this experiment, child supervision is essential.

[techmind]

Neat video:

What you need
A flat-headed screw, 3 to 6cm long
Small, fairly strong round (disc) magnet
20cm of wire
'D' or 'C' cell ALKALINE battery  Do NOT try a rechargeable battery as this would be very dangerous

What you do
Stick the magnet onto the head of the screw
This should magnetise the screw sufficiently that you can hang the pointy end of the screw from the underside of the battery (see video)
Hold one end of the wire to make contact with the top end of the battery
Tickle the other end of the wire on the magnet or screwhead

Caution: Don't hold the wire connected to the screwhead for more than a few seconds as you are effectively short-circuiting the battery - you'll flatten the battery quite quickly and it could even get hot.

Caution: Absolutely DO NOT attempt to use any kind of rechargeable battery (NiCd or NiMH etc) as owing to their much lower internal resistance a very large current will flow, probably enough to melt the wire... at the least you'll burn your fingers, at the worse the battery could explode


It's too late at night for me to figure/explain why it works in detail, but it's all to do with the magnetic field around current-carrying conductors. I'm sure it's much the same explanation as an old experiment where you have a suspended wire dipping in a dish of mercury (probably banned these days!)

If you reverse the battery OR the magnet, the direction of rotation should change.

[paul.fr]

what you need

a clear jar or vase with a wide opening
baking soda, or bicarbonate of soda
vinegar
bubble mix and a bubble ring


what you do


put a few spoons full of baking soda in the jar and pour in some vinegar so it bubbles about halfway up the jar.

when the bubbles settle down a bit, swirl the mixture around to help the baking soda dissolve, then blow some bubbles up nice and high, and catch one in the jar.

what happens to the bubble you caught in the jar?

[paul.fr]

what you need


2 balloons
a piece of rubber hose about 15cm long and wide enough for the balloon mouth to fit around snugly
someone to help you hold the balloons


what you do


blow one of the balloons up to normal size, and get your friend to hold the neck of it tightly while you blow the other one up to half that size

don't tie the balloons off!

put the mouth of the balloons onto the ends of the rubber tubing without letting too much air escape, and without letting go of the neck of the balloon. once both balloons are attached to the tubing, let go of their necks at the same time

what happens!

[paul.fr]

what you need

a marble
a bendy straw


what you do


bend your straw into an L shape and then put the straw in your mouth, so the short bit sticks up like a pipe.
hold the straw in place and balance your marble on the end of the straw, nowblow through the straw.

what happens!

[paul.fr]

what you need

coloured water, cordial, cola...any liquid with a colour
glass
2 straws


what you do

Fill the glass with your chosen liquid, and put one of the straws in and hold it up straight Don't let the straw rest on the bottom of the glass. Now, hold the other straw so the end of it touches the top of the first straw and blow!

what happens?

[daveshorts]

If you want an explanation for the floating marble one has certain similarities to:
http://www.thenakedscientists.com/HTML/kitchen-science/in-lab/exp/the-aerodynamics-of-a-ping-pong-ball/

[paul.fr]

Make a square bubble.

what you need

pipe cleaners
bubble mixture


what you do

use the pipe cleaners to make a 3D square, and dip it in to your bubble mixture. you may get some extra round bubbles, these can be easily popped to leave a nice square bubble.



why does it do that?
when one bubble is surrounded by other bubbles, it can make stable shapes with corners and sides. Try making a 3D triangle...go on..

[paul.fr]

what you need

a bank note
2 paper clips

what you do

fold the note in to a "s" shape, and attach the paper clips where the "o"s are in this very bad diagram
[diagram=290_0]

holding the sides of the note, gently pull to straighten the note out.
what happens to the paperclips?

[paul.fr]

what you need

two coins of the same value

what you do

place one coin in each hand, as shown in the pretty poor diagrams.

left hand.
[diagram=291_0]

right hand.
[diagram=292_0]

yes, they are the worst diagrams you have ever seen....any way. the coin in your right hand should be in the middle of your palm, and the coin in your left hand needs to be close to your thumb..this is obvious in the diagrams!

now turn your hands so they are palm down, where are the coins?


*****can anyone do better diagrams? if you can please feel free to edit mine...please

whats happening

rotational mechanics

When you turn your hands over you're rotating them around their centre point, which is near the middle of your palm. The coin in the middle of your hand will just drop straight down, so it'll stay under that hand. But the coin out near your thumb gets rotated around the centre point of your hand, and that flicks it over under your other hand.

[paul.fr]

In honour of this weeks, Question of the Week - How do Boomerangs Work?

What you need

cardboard or thick paper
a pen or pencil
scissors

What you do

draw a cross shape (like two plasters overlapping to form a cross), and cut it out. slightly bend all four ends in the same upwards direction.

Place your 'boomerang', slightly over the edge of a table and flick it.

[Karen W.]

what you need

two coins of the same value

what you do

place one coin in each hand, as shown in the pretty poor diagrams.

left hand.
[diagram=291_0]

right hand.
[diagram=292_0]

yes, they are the worst diagrams you have ever seen....any way. the coin in your right hand should be in the middle of your palm, and the coin in your left hand needs to be close to your thumb..this is obvious in the diagrams!

now turn your hands so they are palm down, where are the coins?


*****can anyone do better diagrams? if you can please feel free to edit mine...please

whats happening

rotational mechanics

When you turn your hands over you're rotating them around their centre point, which is near the middle of your palm. The coin in the middle of your hand will just drop straight down, so it'll stay under that hand. But the coin out near your thumb gets rotated around the centre point of your hand, and that flicks it over under your other hand.

Yes your thumbs are on the wrong hands! Cool experiment.. I will try it!

[Karen W.]

what you need

two coins of the same value

what you do

place one coin in each hand, as shown in the pretty poor diagrams.

left hand.
[diagram=291_0]

right hand.
[diagram=292_0]

yes, they are the worst diagrams you have ever seen....any way. the coin in your right hand should be in the middle of your palm, and the coin in your left hand needs to be close to your thumb..this is obvious in the diagrams!

now turn your hands so they are palm down, where are the coins?


*****can anyone do better diagrams? if you can please feel free to edit mine...please

whats happening

rotational mechanics

When you turn your hands over you're rotating them around their centre point, which is near the middle of your palm. The coin in the middle of your hand will just drop straight down, so it'll stay under that hand. But the coin out near your thumb gets rotated around the centre point of your hand, and that flicks it over under your other hand.

 ok I tried it, the right hand was definitely as you stated but the left coin did not end up under my other hand.. it ended up right at the outer extension of my left thumb as if my thumb was an arrow pointing to it Right at the tip of my left thumb, but not under my hand!

I was careful to place the coin close to my left thumb and the other in the center of right palm!

[paul.fr]

what you need

A hand


what you do

Bend your middle finger and place the centre section on a table or hard surface. You will be able to lift your thumb, index, and little finger without moving your middle finger. But can you lift your ring finger?

 [ Invalid Attachment ]

[paul.fr]

what you need

A hand
A foot / leg


what you do

Lift your right foot a few inches from the floor and then begin to move it in a clockwise direction. While you're doing this, use your right index finger to draw a number 6 in the air. What happens to the direction you are turning you foot?

[paul.fr]

what you need

2 iron nails
2 glasses (small wine or sherry glasses are ideal)
cooled water (boil a kettle of water then allow the water to cool until it is just warm)
Olive or sunflower oil
Wire wool / fine sandpaper

what you do

Clean each of the nails with wire wool or fine sandpaper. Fill the two of the glasses with cooled water, enough to cover the nail, but leaving a fingers depth unfilled. Add a nail to each of the glasses, and then pour a layer of oil over the water in one of the glasses. The oil will float to the top of the water and form a separate layer which should be about 1cm thick. Leave somewhere where they will not get knocked for 24 hours.

 [ Invalid Attachment ]

What happens to the nails?

[Cameron Lapworth]

This is an oldie but a goodie,

What you need a shallow dish with a flat bottom
a candle
a glass
matches
water.

1.attach the candle to the middle of the dish it will need to hold a certain amount of water so not too flat, a bowl with a flat bottom is ideal.

2. pour a couple of centimeters of water in the dish/bowl and light the candle

3.  put the glass over the candle (candle may need to be cut short to fit, don't use a tea candle).

If you want some sense of mystery don't read below

****************************************

what happens:  as the candle burns the air the volume is reduced inside the glass which is now sealed with the puddle of water in the bottom.  This sucks water from around the bowl/dish up into the glass until the pressure is equaled.