Rotational Mechanics -- A solid sphere is rolled on a rough surface

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Homework Help Overview

The discussion revolves around the dynamics of a uniform solid sphere rolling on a rough surface, specifically focusing on the relationship between linear and angular velocities as the sphere transitions from sliding to rolling without slipping. Participants explore the effects of friction and the conditions under which rolling begins.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the time at which rotation ceases and the implications for angular speed and linear velocity. Questions are raised about the initial conditions of angular velocity compared to the conditions for rolling. There is a focus on determining angular acceleration and its effect on motion over time.

Discussion Status

Some participants have provided calculations related to torque and angular acceleration, leading to a specific time when rotation ceases. However, there is ongoing inquiry regarding the relationship between linear and angular velocities, particularly in the context of pure rolling and the effects of friction.

Contextual Notes

Participants are working under the assumption that the surface is rough, which influences the frictional forces at play. There is also a mention of the initial conditions of the sphere's motion, which may affect the analysis.

Ayesha02
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Homework Statement
A uniform solid sphere of mass M radius R is placed on a rough surface of given an initial linear velocity ##v_0## and angular velocity ##w_0##, where ##w_0## = ##v_0## /2R. plot the graph of angular speed about the center v/s time t.
Relevant Equations
##T## = I* alpha , where T= torque, alpha= angular acceleration
and
##w_0(f)## = ##w_0(i)##- alpha*t
I found out the time when rotation ceases to be 4 ##v_0## /5*mew*g, where mew=coefficient of friction of surface but I am unable to plot the graph post that time
 
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Ayesha02 said:
Homework Statement:: A uniform solid sphere of mass M radius R is placed on a rough surface of given an initial linear velocity ##v_0## and angular velocity ##w_0##, where ##w_0## = ##v_0## /2R. plot the graph of angular speed about the center v/s time t.
Relevant Equations:: ##T## = I* alpha , where T= torque, alpha= angular acceleration
and
##w_0(f)## = ##w_0(i)##- alpha*t

I found out the time when rotation ceases to be 4 ##v_0## /5*mew*g, where mew=coefficient of friction of surface but I am unable to plot the graph post that time
Is the initial angular velocity lower or greater than the one when the sphere rolls? The friction decreases linear velocity and either increases or decreases angular velocity, till rolling occurs. Determine both as functions of time, Show your work in detail.
 
Last edited:
ehild said:
The friction decreases linear velocity and increases angular velocity. Determine both as functions of time, Show your work in detail.

I just did
##T## = 2/5 M R^2 * α
which gives α =5μg/ 2R

hence
##w_0(f)## = ##w_0(i)## - α t
i.e 0= ##v_0##/2R - 5μg/ 2R *t

hence i got t=4##v_0##/5μg (time when rotation ceases)
 
Ayesha02 said:
I just did
##T## = 2/5 M R^2 * α
which gives α =5μg/ 2R

hence
##w_0(f)## = ##w_0(i)## - α t
i.e 0= ##v_0##/2R - 5μg/ 2R *t

hence i got t=4##v_0##/5μg (time when rotation ceases)
You kick a ball. After a short time, does it skid or does it roll?
 
ehild said:
You kick a ball. After a short time, does it skid or does it roll?

Skid initially, after some time rolls.
Im assuming the surface is rough
 
Ayesha02 said:
Skid initially, after some time rolls.
Im assuming the surface is rough
Yes. And what is the angular speed in case of pure rolling with respect to the linear velocity of the CM?
 
Last edited:
ehild said:
Yes. And what is the angular speed in case of pure rolling with respect to the linear velocity of the CM?

Angular momentum conservation

I got the answer:bow:
 

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