Unit 1: Mechanics (Friction) Answers to Exercises

Let’s see how you did! If you didn’t get a few of these, don’t let it stress you out – it just means you need to play with more experiments in this area. We’re all works in progress, and we have our entire lifetime to puzzle together the mysteries of the universe!

Answers:
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1. Friction is the force between one object rubbing against another object. Air resistance, by the way, is the friction of one object rubbing against millions and billions of air molecules.

2. FALSE!!! Walking would be impossible without friction. Your feet couldn’t push back against the floor to move you forward.

3. Air friction slows the feather down. The feather rubs against many, many, many air molecules as it falls through the air. The feather is light and large enough that the air molecules actually slow it down.

4. If you pull the paper slowly, the static friction between the penny and the paper isn’t broken. So the penny rides along with the paper. If you pull it quickly, you can overcome that static friction and the paper will slide along under the penny without moving it. As long as the paper is moving fast enough the kinetic friction between the paper and the penny isn’t enough to move the penny.

5. That objects “stick and slip” as they rub against one another. (Don’t forget, that the magnet thing is a good model but it doen’t work quite like that in the real world.)

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