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More Science Circus Demonstrations


Here are some try-at-home demonstrations from the Shell Questacon Science Circus.

The Liquid Nitrogen Show

See how objects change at temperatures you haven't even dreamt of. We use extreme cold (-196°C) to do some spectacular demonstrations and share some interesting facts. Here's one to try at home.

There's a balloon in my freezer

If you've seen the BOC Liquid Nitrogen show, you may think that you can't repeat any of the experiments at home. WRONG! Although you won't be able to use liquid nitrogen, you can use your humble freezer to shrink a balloon.

What to do

  1. Blow and tie up a balloon to a medium/large size and tie a piece of string tightly around it.
  2. Place the balloon in a freezer for two days (don't remove any food from your freezer to make room for the balloon. We don't want you to starve for science).
  3. Remove your balloon and see if the string is looser, tighter or the same.
  4. Leave the balloon on a window sill for two days. Is there any difference in the tightness of the string now?

What happens?

When gas (in the balloon) is cooled down, it has less pressure and the balloon contracts and takes up less space. You should have noticed that the string was loose after being in the freezer. Once the balloon had been warmed up again near the window, the gas pressure inside should have increased and the balloon increased in size and the string should be fitting snugly again.

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The Fire and Light Show

An action packed show using demonstrations to discover the properties of fire.

Exploding can

WARNING!

Get adult permission and supervision to do this experiment. Make sure there isn't a fire ban and do it outside on a stone or concrete floor, with a bucket of water nearby, just in case.

You will need

  • candle
  • glass jar
  • blue tac or plasticine
  • matches or lighter
  • glass mug or tumbler
  • vinegar
  • baking soda (bicarbonate of soda)

What to do

  1. Stick the candle into the jar with the blue tac. Make sure that the top of the candle is not higher than the top of the jar. If it is, carefully cut a little off the bottom of the candle.
  2. Carefully light the candle
  3. Pour vinegar into the mug until it is about one quarter full.
  4. Add about two teaspoons full of baking soda to the vinegar.
  5. Leave it to fizz.
  6. When it stops fizzing, carefully tip the mug as if you were pouring the air from the top half of it into the jar with the candle. DO NOT let any of the liquid pour out of the mug.
  7. What happens to the candle?

What happens?

When you pour the “air” from the top of the mug into the jar, the candle should go out.

Why?

A fire needs three things to burn. If take any one thing away, the fire will either go out or you won't be able to get it going in the first place.

One of those three things is OXYGEN, which most fires get from the air around them. The other two things the fire requires are FUEL (the wax in the candle) and a source of HEAT (the match) to ignite the fuel.

The fizzing vinegar and baking soda react to make carbon dioxide (CO2) gas (the same gas you breathe out). Carbon dioxide gas is heavier than air, so it stays in the mug. When you pour this gas onto the flame, it goes out because the heavy carbon dioxide smothers the flame and stops it from getting any oxygen from the air around it.

More...

This is how most fire extinguishers work. They release carbon dioxide, foam, powder or water onto a fire to smother or cover it so the fire goes out.

REMEMBER

The mini baking soda extinguisher is no substitute for the real thing).

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The Pressure Show

What would happen to you if you were thrown into outer space? Why is force and area important for pressure (think about a bed of nails or a stiletto shoe heel)? See cool demonstrations using air pressure and the possibility of pain...

The Pressure Show talks about pressure in fluids, especially atmospheric pressure. These two demonstrations show unbalanced pressures.

Levitating Water

You will need

  • Drinking glass
  • Piece of cardboard
  • Water

Fill the glass with water — right up to the very top. Slide the paper card across the top of the glass. Carefully turn the glass upside down, holding the card in place. Gently let go of the card. What happens to the water?

Practice this experiment over a sink or basin until you have mastered it.

What happens?

The atmospheric pressure pushing up on the cardboard (1000 g/cm2) is greater than the weight of the water pushing down on the cardboard (1 g/cm3), so the water stays in place.

Plastic Straw Water Pistol

You will need

  • Plastic straws
  • Glass of water

Cut 1/3 off the end of a straw. Put this into a glass of water. Using the remaining piece of the straw, blow through the straw so that the air passes across the top of the straw in the water. This should produce a spray of water.

What happens?

The air blown out of the straw moves quickly, which makes a low pressure area over the vertical straw. Pressure pushing down on the water in the rest of the glass is stronger than the pressure pushing down on the water in the straw, so the water rises in the straw and can be sprayed like a water pistol.

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