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Q & A: weight of falling can

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Most recent answer: 05/02/2019
Q:
I am a reasonably smart person. I have a good grasp of the Cosmos, gravity, and physics overall. Yet I cannot answer my own question. Which is: Say I am stocking a shelf, with a 16oz can of soda at eye level. And say said can falls from my hand onto the bridge of my foot. Yes it hurts. But what would the can weigh at the time of impact on my foot from the 4 foot drop? Because it seems to weigh a lot more than 16oz. Thank you for your time!
- John A (age 40)
Albuquerque
A:

The weight (force gravity exerts on the can) is the same as usual. When the can is just sitting on your foot, not accelerating the force between it and your foot must just equal the weight. That's why the can isn't accelerating. When the can lands on your foot, it quits moving downward. That means, by definition, that it's accelerating upward. So the force between it and your foot is the usual one plus the force necessary to cause the upward acceleration. That's why it hurts.

This is the reason that soft objects (eg,softballs) don't hurt as much as hard ones (baseballs) when they hit you.  They don't slow down as quickly, so the force that your head exerts on them (and, therefore, the force they exert on your head) is less.

Mike W.


(published on 05/02/2019)

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