The vampires are coming! You need to frighten them away with a loud explosion, but all you have are the things in your house. Here is what you do.

What you need

• empty film canister
• Alka-Seltzer tablet
• water

What you do

1. Place the Alka-Seltzer tablet in the film canister.
2. Add about 1cm of water.
3. Fit the lid on the canister, making sure the seal is tight.
4. Turn the canister upside-down and place it on a flat surface.
5. Stand back!

Scientific explanation

When water is added to the Alka-Seltzer tablet, bubbles of carbon dioxide gas are given off. When the lid is fitted tightly to the canister this gas is contained within an enclosed space. As more gas is given off the pressure inside the canister rises until there is enough force to overcome the seal of the lid. The built up pressure exerts enough force to shoot the canister into the air, forming the explosion.

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