Two Balls Dropped: Separate or Together?

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The discussion revolves around the physics problem of two balls dropped one on top of the other. The initial assumption is that the bottom ball hits the ground first, allowing for a simplified analysis. Participants clarify that while both balls experience the same acceleration, treating them as separate for calculations does not affect the final result. The deformation of the balls during the impact is noted, but it is emphasized that this complexity does not change the outcome. Ultimately, the method of analyzing the situation in stages is justified as a practical approach.
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Hello,

In this problem: http://www.physics.harvard.edu/academics/undergrad/probweek/prob1.pdf

Two balls are dropped, one on top of each other. When figuring out how high the top ball bounces, the solution assumes that the bottom ball hits the ground first, without the other ball on top of it.

I thought that ideally the two balls would stay on top of each other, since they experience the same acceleration, and would both "hit" at the same time. Is something wrong with my thinking?
 
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darkSun said:
I thought that ideally the two balls would stay on top of each other, since they experience the same acceleration, and would both "hit" at the same time. Is something wrong with my thinking?

Hello darkSun! :smile:

No, you're right …

but it doesn't make any difference to the result if we split the equations into two stages …

and since that's easier, that's exactly what we do! :wink:

(technically, of course, the balls deform, and the top of the lower ball doesn't "know" that the bottom has hit the ground until shortly afterwards!)
 
Oh, I see!

It really doesn't make a difference? Seems weird, but I'll try that.

Thank you for the help tiny-tim.
 

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