Distinction between Kinetic Energy and Momentum

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Discussion Overview

The discussion centers on the distinction between kinetic energy (KE) and momentum (p), using a scenario involving a bowling ball dropped into a pool of honey. Participants explore the mathematical representations of momentum and work, and the historical context of Newton's views on these concepts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents an example involving a bowling ball dropped into honey, discussing how momentum is related to the force exerted by the honey over time, and how work relates to the force exerted over distance.
  • Another participant questions the initial reasoning, asserting that momentum is not a force and emphasizing the importance of time and distance in the definitions of work and momentum.
  • A later reply acknowledges the need to correct the example and seeks approval for the reasoning presented to move forward in their studies.
  • There is a discussion about the conditions under which the bowling ball would stop, specifically referencing the buoyant force of the honey and its relationship to the ball's weight.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and relationships between momentum and kinetic energy, with no consensus reached on the initial reasoning or the example provided.

Contextual Notes

Participants highlight the historical context of Newton's views and the implications of time and distance in the definitions of momentum and work, but these aspects remain unresolved within the discussion.

Obliv
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Hello, I would like to provide my thoughts on the distinction between KE and p and would like to know if this reasoning is sound and objective.
I will give an example to start: A bowling ball is dropped from some height into a pool of honey. It is observed that the bowling ball has a velocity V that it falls into the honey with. The time it takes for the bowling ball to reach a velocity VF is observed to be the time t. The distance traveled in the honey before the ball reaches VF is d.

What one would observe to be momentum is the force exerted by the honey onto the bowling ball, to slow it down to VF, during the time interval t.
Written mathematically as: \vec {P} = \int \vec {F}{dt} = {m}\vec {v} = m \int \vec {a}{dt}

What one would observe to be the [change in] kinetic energy or work is the force exerted by the honey onto the bowling ball, to slow it down to VF, through the distance d.
Written mathematically as: W = \Delta {KE} = \int \vec {F} \cdot {d} \vec {x} = m \int \vec {a} \cdot {d} \vec {x}
Newton did not distinguish between momentum and kinetic energy (leibniz did, and his views were not supported).
I don't see why they didn't make a distinction (Newton and his contemporaries, that is). I suppose they did not regard distance as importantly as time since they held the view of absolute time?

edit: If I were to change the velocity of the bowling ball to V+1, (assuming weight is the only force downward) would the time it took to reach VF be t+1? Consequently, would distance traveled then be d2?
 
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Hi
Obliv said:
It is observed
Can you provide a reference ? It seems to me the ball should drop to the floor of the pool and only then stop.

What is your question ? There is no contradiction between ##W = \displaystyle \int \vec F \cdot d\vec s## and ##\vec p = \displaystyle \int \vec F dt##

Obliv said:
one would observe to be momentum is the force
No, a momentum is not a force. Same with work. The presence of time c.q. distance is essential.
 
BvU said:
Hi
Can you provide a reference ? It seems to me the ball should drop to the floor of the pool and only then stop.

What is your question ? There is no contradiction between ##W = \displaystyle \int \vec F \cdot d\vec s## and ##\vec p = \displaystyle \int \vec F dt##

No, a momentum is not a force. Same with work. The presence of time c.q. distance is essential.
Oh you're right. I'll fix the example give me a minute.

If you read the rest of that statement it is the force over the time period t and the integral yields momentum.
I'm not proving any contradictions. I'm merely proving the distinction between the two ideas. I am looking for the approval of this reasoning so that I can move on in my textbook.
 
Alright I fixed it.

The bowling ball would only stop if the buoyant force of the honey was equal to the bowling ball's weight, right? Then the net displacement and time it took to reach zero velocity would be the description I had earlier. I changed it to a specific velocity VF since I want to keep the example as simple as possible.
 

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