Motion of a Sphere: No Friction vs With Friction

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SUMMARY

The discussion focuses on the motion of a sphere subjected to a force parallel to a horizontal surface, analyzing two scenarios: one without friction and one with friction. In the absence of friction, the sphere exhibits purely translational motion. However, when friction is present, it generates a torque that influences the sphere's rotation. The key point of contention is the assertion that no rotational motion occurs under any conditions, which contradicts the understanding that friction can indeed create torque, affecting the sphere's motion.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with concepts of torque and rotational dynamics
  • Knowledge of frictional forces and their effects on motion
  • Basic principles of translational motion
NEXT STEPS
  • Study the principles of torque in rotational motion
  • Explore the effects of static and kinetic friction on motion
  • Investigate the relationship between force, mass, and acceleration in translational motion
  • Examine case studies involving spheres and other objects in motion on surfaces
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Physics students, educators, and anyone interested in understanding the dynamics of motion involving friction and torque in spherical objects.

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Homework Statement


A sphere is resting on a horizontal surface. A force parallel to the surface passing through the center of the sphere is applied.

Describe the motion of the sphere
1. Without any friction
2. With friction.



The Attempt at a Solution



When there's no friction, then the motion is purely translatory. But, if there is friction, it will apply a torque which will force rotation as well as translation. The second part isn't right though. Why?
 
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It cannot apply any torque, because the force goes right through the center of the sphere. What happens is that the friction touching the ball below is the culprit in creating this invisible torque.
 
The force initially applied does not have any torques but it is the friction itself that acts as a torque that rotates the ball equivalent to (frictional force*radius of the sphere)
 
Yeah, that's what I thought, but the book says that there can be no rotational motion under any conditions. I thought the book was wrong but maybe I'd missed something.
 

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