Hot Air Balloon

Make your own hot air balloon

There is something very cool about things that fly - this homemade hot air balloon is no exception.

Suitable for kids aged 8+ with parental supervision

You Need:
  • Garbage Bag
  • Duct Tape (or a plastic packing strip)
  • Hair Dryer

CAUTION This experiment should only be done by adults or under adult supervision. There is a chance the garbage bag will get too hot and start to melt risking a minor burn. The hairdryer could also overheat.

What to do:
  1. Open up the garbage bag and make the bag opening narrow using duct tape or similar. To do this, poke holes in the plastic around the bag opening and thread the tape (or a plastic packing strip) in and out through the holes and secure.
  2. Blow hot air into the garbage bag using the hair dryer directed through the now small opening. Do not leave the hairdryer on for too long or the plastic may start to melt and weigh the bag down.
  3. After a few seconds, when the garbage bag is full of hot air, turn off the hairdryer and let go of the bag.
  4. The bag begins to rise towards the ceiling and hovers for sometime. When it comes back down, fill the bag with more hot air and let go again. You may have to repeat this a few times before the bag actually reaches the ceiling.

Why is it so?

The particles, or atoms, making up hot air have more energy and therefore move faster than air at cooler temperatures. Because they are on the move, the hot air particles take up more space in the garbage bag than cooler air particles. This means there are fewer air particles inside the hot air balloon compared to the outside atmosphere. With less particles, the bag is lighter than the surrounding air, allowing it to rise. When the air inside the bag cools down and the particles slow down making more room, this allows more air to enter the bag making it heavier and sinking it to the floor. Real hot air balloons work on this same principle: that hot air rises. Heat is turned up to get the balloon higher and turned down to sink the balloon lower. Try standing on a table and reach toward the ceiling, you will notice it is warmer up there than near the floor.