napncrash t1_iugnia1 wrote on October 31, 2022 at 4:24 AM

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."

KhaleesiDog t1_iugrei5 wrote on October 31, 2022 at 5:10 AM

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

Skusci t1_iugufzi wrote on October 31, 2022 at 5:51 AM

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

KhaleesiDog t1_iugv8rt wrote on October 31, 2022 at 6:02 AM

It flexes at the point of impact.

[deleted] t1_iuh5eof wrote on October 31, 2022 at 8:38 AM

[deleted]

Terravash t1_iuhdmlo wrote on October 31, 2022 at 10:39 AM

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.

TheJeeronian t1_iuhxav4 wrote on October 31, 2022 at 1:50 PM

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

MrWedge18 t1_iugqhll wrote on October 31, 2022 at 4:59 AM

"For every action, there's an equal and opposite reaction"

Basically, what it's saying is forces always comes in pairs. For every force, there's an equal force in the opposite direction.

The force pushing air out of a balloon has an equal and opposite force that pushes the balloon forward.

The force from a boat's propeller pushing water backwards has an equal and opposite force that pushes the boat forwards.

The force that shoots a bullet out of a gun has an equal and opposite force that causes the gun to recoil.

Mp32pingi25 t1_iugmt6t wrote on October 31, 2022 at 4:16 AM

when you jump, your legs apply a force to the ground, and the ground applies and equal and opposite reaction force that propels you into the air.

cocompact t1_iugobdo wrote on October 31, 2022 at 4:33 AM

If your question is about how anything can move at all "by Newton's third law", please see https://physics.stackexchange.com/questions/45653/given-newtons-third-law-why-are-things-capable-of-moving

VulcanVisions t1_iuk0y86 wrote on October 31, 2022 at 10:31 PM

When object A acts on object B, object B also acts on object A, but on the opposite way.

For example, picture a cat sitting on the floor.

The earth is pulling the cat down through gravity, but the cat is also pulling the earth up through its gravity.

These forces are opposite but equal to each other.

ELI5: Newton's third law

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