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255

ur dada so buff he falls significantly faster than g (mander.xyz)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

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The bowling ball isn’t falling to the earth faster. The higher perceived acceleration is due to the earth falling toward the bowling ball.

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[–] [email protected] 13 points 3 weeks ago (1 children)

Uh... That's not how that works. The distance between two objects changes with acceleration a1-a2 where object 1 moves with acceleration a1 and object 2 a2 (numbers interchangeable). In the bowling ball's case a2 is the same but a1 is bigger in the negative direction so the result is that the bowling ball falls faster.

[–] [email protected] 10 points 3 weeks ago (2 children)

Calculate the force between the earth and the bowling ball. It'll be G • (m(earth) • m(bowling ball)) / (r = distance between both mass centers)²

Simplify. You're getting g • m(bowling ball).

Now do the same for the feather. Again, the result is g • m(feather).

Both times you end up with an acceleration of g. If you want to put it that way: The force between the earth and the bowling ball is m(bowling ball)/m(feather) times as high as the force between the earth and the feather, but the second mass also is m(bowling ball)/m(feather) times as high, resulting in the same acceleration g.

Higher force on same mass results in stronger acceleration. Same force on higher mass results in lower acceleration. Higher force on equally higher mass results on equally high acceleration.

I just asked my professor this exact thing (if the ball would get to the earth sooner because it accelerates the earth towards it) like two weeks ago and my previous message + this message was his explanation.

PS: If you're looking at this from outside, the ball travels less distance before touching the ground (since the ground is slightly nearer due to pulling the earth more towards it), but also accelerates slower while accelerating the earth faster towards it. The feather gets accelerated faster towards the earth and travels a longer distance before touching the ground but doesn't accelerate the earth as fast towards it.

But because we're not outside, we only care about the total acceleration (of the earth towards the object and the object towards the earth), and that's g. We don't notice if (fictional numbers) the earth travels 1m and the object travels 1m or if the earth stays in place and the object travels 2m, what matters for us is how long it takes an object 2m away from the earth to be 0m away from the earth.

[–] [email protected] 11 points 3 weeks ago (1 children)

So let's just look at that again. The bowling ball's (mass m1) acceleration is GM/R². The feather's is also GM/R². They have the exact same acceleration, which is g. I'm not sure where you're getting that the bowling bowl accelerates slower. Meanwhile in the bowling ball's case the Earth's acceleration is higher, as you already said. This results in less free fall time overall.

[–] [email protected] 1 points 3 weeks ago (1 children)

The acceleration relative to the earth is the same, relative to some point from another system the bowling ball accelerates very slightly slower but accelerates the earth very slightly more towards it. The total acceleration of these two bodies towards each other is g.

[–] [email protected] 1 points 3 weeks ago

Yeah you're making that statement but it's not true. Their acceleration relative to an inertial reference frame is g. That's what the law of universal gravitation says, I have no idea where you're getting that stuff from.

[–] [email protected] 2 points 3 weeks ago (1 children)

You said the two objects accelerate at the same rate, but then in the PS you said the feather gets accelerated faster. What do you mean?

Are you saying the feather gets pulled on more because the mass of earth minus feather is greater than the mass of earth minus ball? You would be right. If you lift the feather, measure how long it takes to fall, then lift the ball and measure, you should get the same number. This meme was assuming you either let them fall side by side, or measure them separately but each time conjure the object out of thin air.

[–] [email protected] 2 points 3 weeks ago (1 children)

You said the two objects accelerate at the same rate, but then in the PS you said the feather gets accelerated faster. What do you mean?

Both accelerate at the same rate relative to the earth (the bowling ball accelerates slightly slower relative to some outside point, but it accelerates the earth slightly more towards it, resulting in the same relative acceleration to the earth as the feather)

[–] [email protected] 4 points 3 weeks ago

Newton's second law works in inertial frames. The acceleration of both objects would be the same in the inertial frame. But in the inertial frame, the earth would accelerate faster toward the object if the object was a bowling ball than if it was a feather.