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napncrash t1_iugnia1 wrote

Forces, the way Newton described them, change motion.

So when you throw a tennis ball against a wall, the tennis ball obviously applies a force to the wall.

What's less obvious is that the wall applied a force to the tennis ball. Did the motion of the ball change? Yes it did. What caused it? The wall. So, using Newton's terms, the wall applied a force to the ball.

Turns out, the wall applies the exact same amount of force back as the ball applied forward.

*EDIT: The comments below are excellent expansions. The wall doesn't seem to move, but there are vibrations throughout the wall (and so on) that account for that force. And yes, many other forces are acting on the wall.

EXPLAIN IT TO ME LIKE I'M 10: Maybe it's better to say "forces affect inertia - they can help or hurt it."

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KhaleesiDog t1_iugrei5 wrote

Did the motion of the wall change? Yes it did.

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Skusci t1_iugufzi wrote

Being rigidly attached to the 6.6 sextillion tons of planet earth does tend to diminish the magnitude of the change in motion though.

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KhaleesiDog t1_iugv8rt wrote

It flexes at the point of impact.

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Terravash t1_iuhdmlo wrote

Given the density of a standard wall (assumed concretish) vs a tennis ball, surely you'd be going smaller than a micrometer to measure flex.

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TheJeeronian t1_iuhxav4 wrote

Our walls here are usually drywall with supporting wooden studs. The flexure is invisible but easily measured

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