Make hot air balloons using a toaster
toaster, cardboard box, pedal bin thin bin bags
Put your toaster and the cardboard on a heatproof surface, as near the floor as you can. A metal chair could work well.
remove the bottom of the cardboard box and cut a hole large enough to fit the toaster through in the top of the box.
Open up a bin bag and wave it around so it has some air inside. Check the mouth of the bag will fit across the top of the cardboard. Then remove the bag.
Take the cardboard box off the toaster.
Set the toaster to run for about 1 minute.
Place the box over the toaster.
Fit the bag over the cardboard and lower it 5â€“10cm down the outside. Lightly hold the bag on the cardboard with your fingers.
Wait 15â€“20 seconds and the bag will start to lift.
Safety: Once the bag is clear of the cardboard, stop the toaster or switch it off at the wall socket.
Once the toaster is running, don't touch the toaster. Don't let the bag droop near it either.
The toaster warms up the air that's in the bag. Most things expand when they get warmer, including the air inside the bag. The trapped air wants to fill a larger volume and the bag puffs up.
Once the bag can't puff up any more, expanding air is instead forced out of the bag's open end.
The bag now has the same volume of air in it, but that air weighs less than when it was colder. (Its density is reduced.)
So a litre of warm air inside the bag weighs less than a litre of room air outside the bag.
A pocket of air surrounded by something more dense has buoyancy and will rise, just like an air bubble underwater. The buoyancy of the warm air is enough to lift a very light plastic bag.