Direction of friction in rotation

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SUMMARY

The direction of friction for rolling objects is determined by their acceleration and the nature of their motion. When a ball rolls down an incline, the friction force acts upward along the surface, opposing the acceleration due to gravity. This friction is zero for a rolling object that is not accelerating or decelerating. In contrast, a sliding object converts energy into heat, which affects its acceleration differently than a rolling object.

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  • Understanding of Newton's laws of motion
  • Basic principles of rotational dynamics
  • Knowledge of kinetic and potential energy
  • Familiarity with the concept of friction in physics
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  • Research the role of friction in rolling motion
  • Study the effects of inclined planes on object motion
  • Explore the differences between rolling and sliding friction
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phoenixruby
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could someone please explain the technique of how to know the direction of friction in case of rolling.

eg. when a ball is rolling down an inclined or up or hits a wall and rebounds etc.
 
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In the case of a rolling object, the friction force on a rolling (and not slipping) object is zero unless the object is accelerating (or decelerating). Friction force will oppose the acceleration of a rolling object, resulting in an increase in angular velocity (assuming no slippage). So if an object is being accelerated due to gravity on an inclined plane, the friction force will be along the surface of the plane, in the "upward" direction. This retards the rate of linear acceleration, since the gravitational potential energy is used to increase both the linear and angular kinetic energy of a rolling (but non slipping) object. In the case of a sliding object, some of the energy is converted into heat, also reducing the rate of acceleration.
 

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