Some questions about terminology

Click For Summary

Discussion Overview

This discussion revolves around terminology and concepts related to physics problems involving friction and thermal energy. Participants explore the implications of phrases like "sliding past point P" and the correctness of a proposed equation for calculating thermal energy in a friction scenario.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether "sliding past point P" implies stopping at P or continuing beyond it, suggesting it means not stopping at P.
  • Another participant challenges the proposed equation ΔTE = μmgt, asking for its intended use and the assumptions behind it.
  • Concerns are raised about the derivation of the equation, with one participant noting that work is defined as force times distance, not force times time.
  • A participant emphasizes the importance of context, suggesting that if a problem specifies calculating the minimum initial velocity for an object to just slide past P, it would imply stopping immediately after P.
  • One participant proposes using conservation of energy principles to calculate the thermal energy added to an object, indicating that the input of kinetic energy should be considered.
  • Another participant suggests calculating potential and kinetic energy in the system and subtracting that from the total input of kinetic energy to find the remainder as heat.
  • There is a discussion about the methods and principles that could be used, including free body diagrams, Newton's Laws, and the work-energy theorem.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of terminology and the validity of the proposed equation. There is no consensus on the correct approach to calculating thermal energy in the given scenario, and multiple competing views remain.

Contextual Notes

Participants have not fully derived the proposed equation, and there are unresolved assumptions regarding the conditions under which the calculations are made, such as the nature of the surface and the treatment of energy loss.

AndyCh
Messages
3
Reaction score
0
I thought this would be the most logical way to post this, but give me some grace if it is not because this is my first time posting on this site (then relinquish the grace and tell me how to do it properly haha).

First: When a physics problem says "sliding past point P" does that mean it stops after reaching point P, or slides an arbitrary amount past point P?

Second: Is this equation correct?

ΔTE = μmgt

Where TE is thermal energy (ΔTE is heat), μ is the coefficient of friction, g is the local gravity, and t is time

assuming there is no heat transferred to the 'track' (that which the object whose mass and thermal energy is in question is sliding upon) or the air surrounding.
 
Physics news on Phys.org
AndyCh said:
I thought this would be the most logical way to post this, but give me some grace if it is not because this is my first time posting on this site (then relinquish the grace and tell me how to do it properly haha).

First: When a physics problem says "sliding past point P" does that mean it stops after reaching point P, or slides an arbitrary amount past point P?
It just means that it does not stop at point P.

Second: Is this equation correct?

ΔTE = μmgt

Where TE is thermal energy (ΔTE is heat), μ is the coefficient of friction, g is the local gravity, and t is time
Depends, what is it supposed to tell you and under what circumstances?

Looks like you are assuming sliding with friction along a horizontal, flat, surface and that all the energy dissipated by the friction ends up as heat in whatever is sliding. Then it does not look right no. How did you derive it?

Note: work is change in energy is force times distance, not force times time.
 
Context is everything. For example if the problem said something like "calculate the minimum initial velocity so that the ice puck just slides past point P" then you would base your calculations assuming it stops immediately after P.

Have you got an example problem?
 
I didn't really derive it with any particular technique, I just thought it made sense.
How would I calculate the addition of thermal energy to an object in this situation then:

An object with mass m and initial velocity v slides across a track. The friction coefficient between the object and the track is μ. This takes place on the surface of earth.
It is assumed that no heat is transferred to the track, or air surrounding.
 
AndyCh said:
I
An object with mass m and initial velocity v slides across a track. The friction coefficient between the object and the track is μ. This takes place on the surface of earth.
It is assumed that no heat is transferred to the track, or air surrounding.
Hint: conservation of energy. You have a fixed input of kinetic energy.
 
jbriggs444 said:
Hint: conservation of energy. You have a fixed input of kinetic energy.
So I would calculate potential and kinetic energy in the system, then subtract that from the total input of kinetic energy to get the remainder as heat!
 
AndyCh said:
I didn't really derive it with any particular technique, I just thought it made sense.
How do you know it makes sense if you did not derive it?

How would I calculate the addition of thermal energy to an object in this situation then:
An object with mass m and initial velocity v slides across a track. The friction coefficient between the object and the track is μ. This takes place on the surface of earth.
It is assumed that no heat is transferred to the track, or air surrounding.
I would use my understanding of:
Free body diagram + Newton's Laws.
Work-energy theorem.
suvat equations.

So I would calculate potential and kinetic energy in the system, then subtract that from the total input of kinetic energy to get the remainder as heat!
... did you try that?
 

Similar threads

  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 35 ·
2
Replies
35
Views
5K
  • · Replies 22 ·
Replies
22
Views
6K
  • · Replies 152 ·
6
Replies
152
Views
11K
  • · Replies 37 ·
2
Replies
37
Views
5K