Newton's laws of motion discussion question

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Discussion Overview

The discussion revolves around the question of why kicking a large rock might hurt more than kicking a small pebble, particularly in the context of Newton's laws of motion. Participants explore the implications of force, mass, and acceleration, as well as the role of impulse and momentum in this scenario.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that applying the same force to both a pebble and a rock leads to different accelerations due to their differing masses, questioning how this relates to the sensation of pain when kicked.
  • Another participant challenges the assumption that the same force is applied to both objects, suggesting that a larger object may require a greater force to kick.
  • A participant argues that the force felt by the foot is determined by the force applied, implying that the mass of the object only affects its own acceleration, not the acceleration of the foot.
  • One participant introduces a hypothetical scenario involving two rocks of similar appearance but different masses, questioning whether kicking a heavier rock must always hurt more, and suggesting that the force applied can vary based on how hard one kicks.
  • Another participant discusses the impulse-momentum perspective, noting that when kicking a heavy rock, the foot may bounce back, potentially contributing to the sensation of pain, while a lighter object accelerates more and moves forward.

Areas of Agreement / Disagreement

Participants express differing views on whether the sensation of pain is solely dependent on the force applied or if it is influenced by the mass of the object being kicked. There is no consensus on the relationship between mass, force, and the resulting pain experienced.

Contextual Notes

Some assumptions about the nature of the kick, the forces involved, and the definitions of pain and acceleration are not fully explored, leaving room for further discussion.

madah12
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this is from chapter 4 of university physics of young and freedman
q19 why can it hurt your foot more to kick a big rock than a small pebble? must the big rock hurt more? explain?
but I can't see the answer at all by just applying Newtons law
in the scenario of the small pebble
mp is small
you apply a force F to the pebble it applies the same force on your foot and get ap = F/mp
and you get af=F/mf

incase of the large rock
mr>mp

but the same F is applied the acceleration =F/mr
and af=F/mf
so the acceleration of your foot is independent of the mass of the kicked object as I see and the only difference is that the pebble will get more acceleration so how by Newtons laws can I answer this question? is it related to other concepts? if so why ask it in the Newton's laws section?
 
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You are assuming that you apply the same force to both pebble and rock. But which is most likely to require generating larger amounts of force? Which is harder to accelerate?
 
well in the question you only kick the rock you don't have to move it the same distance but ok if you want me to assume that you want to accelerate the rock the same acceleration of the pebble then the it would always hurt more to hit the heavier rock so the second part doesn't make sense...
but my point is that it doesn't matter why what do you kick because the force you will feel is the force you will apply right? the kicked object's mass only affect the acceleration "it" not the acceleration I would received right?
 
madah12 said:
well in the question you only kick the rock you don't have to move it the same distance but ok if you want me to assume that you want to accelerate the rock the same acceleration of the pebble then the it would always hurt more to hit the heavier rock so the second part doesn't make sense...
Imagine you have two identical-looking rocks in front of you. Unknown to you, only one is a real heavy rock, the other is just a light, plastic fake rock. You attempt to kick each one in a similar manner with a hard, swift kick. What happens?

As far as part 2 goes, it seems ambiguous. Does kicking a heavy rock have to hurt more? Of course not. Kick the rock very lightly; kick the pebble as hard as you can.
 
Doc Al said:
Imagine you have two identical-looking rocks in front of you. Unknown to you, only one is a real heavy rock, the other is just a light, plastic fake rock. You attempt to kick each one in a similar manner with a hard, swift kick. What happens?

As far as part 2 goes, it seems ambiguous. Does kicking a heavy rock have to hurt more? Of course not. Kick the rock very lightly; kick the pebble as hard as you can.

the light one will accelerate more while the heavy one will accelerate less
also how do we look at this from impulse momentum point of view? from experience when I kick a heavy rock my feet bounce back a little but if i hit a small one it goes forward so is the impulse at the first scenario bigger than the initial momentum but opposite in direction? while it isn't bigger in the second? does the fact the my feet bounce back have to do with the amount of pain my I feel?
 
madah12 said:
the light one will accelerate more while the heavy one will accelerate less
And what does that say about the acceleration of your foot?
 

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