Why Doesn't the Energy Method Require Friction for Rolling Objects?

  • Thread starter Thread starter RRachev
  • Start date Start date
  • Tags Tags
    Incline Rolling
Click For Summary

Homework Help Overview

The discussion revolves around the energy method applied to a rolling object, specifically a cylinder rolling down an incline without slipping. Participants are exploring why friction does not need to be accounted for in the energy method while still arriving at the correct velocity for the object.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the presence of friction, questioning whether it is kinetic or static. They compare results from the energy method and force method, noting that both yield the same velocity despite differing considerations of friction.

Discussion Status

The conversation is ongoing, with participants clarifying their understanding of static friction and its role in the context of the problem. There is an exploration of interpretations regarding the type of friction involved, but no explicit consensus has been reached.

Contextual Notes

The original problem does not specify the type of friction, leading to varying interpretations among participants. The discussion highlights the assumptions made in applying the energy method without friction.

RRachev
Messages
5
Reaction score
0
An object (for example cylinder) is rolling down an incline, with no slip. We know there is some friction and we have to find the velocity of the objects. There are 2 ways of doing so with calculating resultant force and using Newton's laws and the energy method. Why is it that when we are using the energy method we don't have to take into account the friction and our answer is still right?

Mass - m
Radius of the cylinder - r
Moment of Inertia - I=(mr^2)/2
Distance traveled - s
Angle of Incline - θ
Acceleration due to gravity- g

I know the answer is v= sqrt(4*s*g*sinθ/3)

Thanks in advance
 
Physics news on Phys.org
What type of friction is present, kinetic or static?
 
The question did not say. But when you compute the velocity using the force method or the energy method (while using the second one assume no friction force) and the answer is the same. I do not quite understand the solution probably that's the problem itself.
 
The problems inadvertently says it, I'm asking what your interpretation of the problem is, do you think the friction keeping the cylinder from slipping is kinetic or static?
 
Ohh now I see what you mean. Should be static?
 
Correct. Can static friction do work on an object?
 
No.
Yeah thanks a lot for the help.
 

Similar threads

Kinetic Energy of a Cylinder Rolling Without Slipping
  • · Replies 21 ·
Replies
21
Views
5K
Why is the direction of kinetic/static friction up a ramp?
  • · Replies 7 ·
Replies
7
Views
2K
How can we model a rolling truck on an incline using rotational motion analysis?
  • · Replies 24 ·
Replies
24
Views
3K
Wooden sphere rolling on a double metal track
  • · Replies 97 ·
4
Replies
97
Views
6K
A cylinder of snow rolls down a hill gathering more snow -- calculate its speed
  • · Replies 39 ·
2
Replies
39
Views
4K
Distance rolled of sphere vs cylinder with same m, r, and v
  • · Replies 5 ·
Replies
5
Views
1K
Ring and solid sphere rolling down an incline - rotation problem
  • · Replies 8 ·
Replies
8
Views
4K
Friction Required for Billiard Ball to Roll without Slipping
  • · Replies 60 ·
3
Replies
60
Views
5K
Cylinder Rolling Down an Incline Without Slipping
  • · Replies 7 ·
Replies
7
Views
4K
Constraints on a hoop rolling on a cylinder
  • · Replies 1 ·
Replies
1
Views
3K