Your students probably know all about Fig Newtons (they’re fruit and cake!), but what about Sir Isaac H. Newton? Specifically, his third law of motion: “Every action has an equal and opposite reaction”—do they know that jam? This handy dandy Demo Science science demo will help you demonstrate Newton’s Third Law, as well as teaching your students a little something about air and air pressure.
The Answer, My Friend, Is…
For this experiment, all you’ll need is one balloon. The bigger the better.
Blow that sucker up as big as you can get it. (Make sure to have a few backups on hand in case you get a little overzealous whilst inflating.) Hold the balloon closed (don’t tie it off) and explain to your smelly students why the balloon looks like it does when inflated. Specifically, the balloon is large and round because the air pressure inside pushes outward, equally in all directions.
Instruct your students to observe the balloon closely for the next part. Then, let go and watch as the balloon zips wildly around the room. Why did that happen, kids?
Blowin’ In the Wind
Once you let go of the balloon, the air inside is no longer pushing equally outward; instead, it pushes its way out through the mouth of the balloon. This happens because the air pressure inside the balloon was higher than the air pressure outside of it. In almost all cases in science and nature, air moves from higher to lower pressure concentration.
As the air rushes out of the balloon in one direction, the balloon travels in the opposite direction. This, then, is Newton’s Third Law in action. The air blasting out is the action; the balloon jetting across the room is the reaction.