Take an unused teabag. Carefully remove the staple, empty its contents and...
stand the empty teabag on a non-flammable surface like a tall cylinder. If you have any holes in the teabag, this demonstration will not work. If you have trouble removing the staple without making the staple hole any bigger, than trim off the end of the teabag that has the staple with scissors. If you do this, however, it needs to be a straight cut so that the tea bag can stand up on the surface you are using and you don't want to cut off too much because you want a long cylinder.
Light the top of it on fire with a match or lighter.
It will burn down quite a bit and you will begin to think that it is just going to burn up and nothing will happen. Another failed experiment?
And then, suddenly, whooosh....it takes off!
It's a fun demonstration that they will want to see again and again, but what is the science behind it?
"As the flame burns down the bag of tea, it heats the air that is contained within the cylinder. The heat excites individual air molecules and causes them to move more quickly and spread out within the cylinder. The excited air molecules inside the cylinder are farther apart than those on the outside of the cylinder, making the air inside the cylinder less dense than the air outside the cylinder. This warmer, less dense air rises above the cooler, more dense air. This creates a thermal, or convection, current. The space created by the less dense air inside the cylinder allows the dense air outside to push upwards from the bottom. That movement or current of air is referred to as a convection current. Since the ash is so lightweight, the force of the rising hot air is strong enough to lift the ash into the air. Hot air balloons use a similar method to your rocket that you created with a bag of tea. Hot air balloons use a burner to heat the inside of the balloon, creating the same air density change that you made with your rocket. However, there is no mass change like when your paper turned to ash. Instead, the air inside the balloon is heated much hotter than the air outside, creating an envelope of air much less dense than the air outside. As a result, the balloon lifts off the ground."-Steve Spangler Science