To understand how "thrust" propels an object
- Piece of string approximately 10 feet long
- Plastic straw (straight and large enough to thread the string through)
- Two helpers (chairs or sturdy door handles about 10 feet apart will also work)
Thread the string through the plastic straw. Have the helpers hold the string, about ten feed apart, making sure the string is taut and straight so there is no upward or downward slope. (Or tie the strong to something.) Blow up the balloon (this is the part that’s like filling a rocket engine with fuel) and pinch the opening with your fingers to keep the air inside. (Don't tie it off.) While pinching the end of the balloon, secure it onto the bottom of the plastic straw with a few pieces of tape. Pull the full balloon with the straw to one end of the string, so that its opening faces in the opposite direction from the clear line of string ahead of the balloon. Let go of the balloon, then release its opening.
Even though you did not fill the balloon with rocket fuel, it was able to propel forward. In fact, the balloon is so light that all it needs is a jet of air to create enough thrust to get it to move through space. Try it again with the balloon only half inflated or try other sizes and shapes of balloons.