EasyPhysicsHigh School (9–10)GeneralMechanics › Momentum and CollisionsMechanics › Newton's Laws of MotionConceptualBoard Exam
You blow up a balloon and let it go. It zooms round the room…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
You blow up a balloon and let it go. It zooms round the room.
- Which object pushes on which, and which way?
- Does the balloon push against the walls or the room's air to move?
- Would it move in a room with no air?
Need a reminder? The key ideaShow
Newton's third law: when A pushes B, B pushes A with a force of the same size in the opposite direction. The two forces act on different objects, so they never cancel each other.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The balloon squeezes the air inside out backwards; the air pushes the balloon forward.
Step 2. (b) No. It pushes against its own escaping air.
Step 3. (c) Yes. It needs only the air inside it; the room's air only slows it down.
Answer: Balloon and its air push each other; it does not need the walls or the room's air.
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