Today we’ll inflate a balloon with a microwave!
Warning: Please ask an adult to help, and use oven mittens.
Materials:
- Water
- Balloon (non-metallic!)
- Microwave
Instructions:
- Fill a balloon with a small amount of water. Just a few spoons worth, the balloon doesn’t need to be full nor expand. Tie a knot.
- Place the balloon in the microwave and microwave it on high power for 10-20 seconds. Repeat if nothing happens. Don’t make the balloon burst!
- Carefully open the microwave door. Be careful, the balloon is hot!
- Allow the balloon to cool for a few minutes. As the steam inside the balloon cools and condenses, it will turn back into liquid water.
The balloon expands because the water inside it is heated and turns to steam, which takes up more space than the water did in its liquid form. Over 1000 times as much space!
When a substance is heated, the energy of its particles increases, causing them to vibrate more and take up more space. This is because the average kinetic energy of the particles, or their movement, increases with temperature. When the particles are moving faster and have more energy, they need more space to move around in.
On the other hand, when a substance is cooled, the energy of its particles decreases, causing them to vibrate less and take up less space. The average kinetic energy of the particles decreases with temperature, so the particles need less space to move around in.
So when the water inside the balloon is heated by the microwave and turns to steam, it expands and takes up more space, causing the balloon to inflate. As the steam cools and turns back into a liquid, it contracts and takes up less space, causing the balloon to deflate.
BONUS! Water is one of the few substances that doesn’t take up less space when freezing. It is one of the few substances that expands! The molecules organize in the form of rings when freezing. This is why freezing a bottle is a bad idea, as it might burst.
Another substance that expands as solid is the metal bismuth. Usually, metals contract when cooled (this is being used sometimes to fit parts together in production).