Solving Angular Momentum Problems with Linear & Angular Acceleration

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SUMMARY

This discussion focuses on solving angular momentum problems involving a sphere transitioning from sliding to rolling motion. The key parameters include the initial linear speed (V_{cm}), initial angular speed (\omega), and the coefficient of kinetic friction (\muk). The frictional force generates both linear acceleration and torque, leading to angular acceleration. The critical relationship established is that the ball stops sliding when V_{cm} equals \omega multiplied by the radius (r), indicating the transition to smooth rolling.

PREREQUISITES
  • Understanding of classical mechanics principles, specifically angular momentum and torque.
  • Familiarity with the concepts of linear and angular acceleration.
  • Knowledge of the moment of inertia and its calculation for different shapes.
  • Basic proficiency in applying Newton's laws of motion to rotational dynamics.
NEXT STEPS
  • Study the relationship between linear and angular motion in rolling objects.
  • Learn how to calculate the moment of inertia for various geometries.
  • Explore the effects of friction on motion, particularly in transitioning from sliding to rolling.
  • Investigate the equations of motion for objects under the influence of both linear and angular acceleration.
USEFUL FOR

Students studying classical mechanics, physics educators, and anyone seeking to deepen their understanding of angular momentum and motion dynamics in rolling objects.

staf9
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I know this sounds weird, but I studied QM and GR before classical physics, and I'm just lost when it comes to angular momentum problems.

Homework Statement


A sphere is moving along a lane. It slides initially then rolls. The initial speed is [tex]V_{cm}[/tex] and initial angular speed [tex]\omega[/tex]. The coefficient of kinetic friction between the ball and the lane is also known. The kinetic frictional force acting on the ball causes a linear acceleration of the ball while producing a torque that causes an angular acceleration of the ball. When [tex]V_{cm}[/tex] has decreased enough and [tex]\omega[/tex] has increased enough, the ball stops sliding and rolls smoothly.

Given: [tex]V_{cm}[/tex] initial, [tex]\omega[/tex] initial, [tex]\mu[/tex]k.

What is [tex]V_{cm}[/tex] in terms of [tex]\omega[/tex]?

While the ball is sliding, what is the ball's linear and angular acceleration?

How Long does the ball slide?

How Far does the ball slide?

What is the linear speed of the ball when smooth rolling begins?

Homework Equations



We know since it is sliding initially that the initial angular speed is zero

R[tex]f_{s}[/tex] = [tex]I_{cm}[/tex][tex]\alpha[/tex]

Beyond this, I'm lost.
 
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The friction is a product of [itex]\mu_k[/itex] and the weight (mg) or normal force to the horizontal surface.

The friction causes the ball to decelerate in terms of linear or translational motion while all causing the wall to increase in rotational velocity, i.e. the friction induces angular acceleration.

For moments of inertia, see - http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html, and
http://hyperphysics.phy-astr.gsu.edu/hbase/isph.html#sph

The ball stops sliding when Vcm = [itex]\omega[/itex]r, i.e. the tangential speed at the radius = translational speed.
 

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