Moment of inertia rolling down a hill

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SUMMARY

When two solid spheres, one large and massive and the other small and low mass, roll down a hill, they reach the bottom simultaneously. This conclusion is based on the principle of rolling without slipping, where both gravitational force and moment of inertia play crucial roles. The moment of inertia for a solid sphere is given by the formula ICM = (2/5)MR², but in this scenario, the mass and radius cancel out, leading to equal acceleration for both spheres. Therefore, despite differences in mass, both spheres arrive at the bottom at the same time.

PREREQUISITES
  • Understanding of rolling motion and the concept of rolling without slipping.
  • Familiarity with the moment of inertia, specifically for solid spheres.
  • Basic knowledge of gravitational forces acting on objects.
  • Ability to apply Newton's laws of motion in rotational dynamics.
NEXT STEPS
  • Study the principles of rolling without slipping in detail.
  • Learn how to derive and apply the moment of inertia for different shapes.
  • Explore the relationship between linear and angular acceleration in rolling objects.
  • Investigate the effects of mass distribution on the motion of rigid bodies.
USEFUL FOR

Students studying physics, particularly those focusing on mechanics and rotational dynamics, as well as educators seeking to clarify concepts related to rolling motion and moment of inertia.

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Homework Statement



Two solid spheres -- a large, massive sphere and a small sphere with low mass -- are rolled down a hill. Which one reaches the bottom of the hill first?

Homework Equations



ICM= (2/5)MR2

The Attempt at a Solution



I thought that this would be the smaller sphere because it has a lower moment of inertia… but this isn't right. Can someone please explain?
 
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You have to do the physics ... what are the forces on the cylinders and the constraints?
Have you just done a lesson or so on rolling without slipping?
 
What physics do I have to do? My teacher talked about it a little… but honestly he is not very good at explaining things so I am having trouble understanding this.
 
Just gravity is acting on them right? So the larger, more massive one would reach the bottom first?
 
The wheel has to roll as well - so it will have an angular velocity.
Have a look at how other's do it.
http://faculty.wwu.edu/vawter/PhysicsNet/Topics/RotationalKinematics/RollingWithoutSlipping.html
https://www.physicsforums.com/showthread.php?t=169313
... there are also video tutorials on youtube.
 
Last edited by a moderator:
okay so since the masses and radii drop out, they reach the bottom at the same time?
 
why would the masses and the radii "drop out" - did you do any math?
 
that's what it was on your second example… What math am I supposed to do??
 
Have you had a look at the links I have given you?
 

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