Question about static friction and energy loss

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Discussion Overview

The discussion revolves around the role of static friction in the context of energy transfer during deceleration. Participants explore how static friction affects kinetic energy and whether it contributes to energy loss in mechanical systems, particularly in scenarios involving a car or a box on a truck that is braking.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that static friction can cause both acceleration and deceleration of an object, questioning the fate of mechanical energy when kinetic energy decreases.
  • Another participant provides an example of a car slowing down, stating that static friction does not do work, and suggests that the mechanical energy is converted into internal energy within the car, such as in the brake pads.
  • A participant references their textbook, describing a scenario where a box on a braking truck decelerates due to static friction, expressing confusion about the conversion of kinetic energy to internal energy.
  • Further clarification is offered that the box's kinetic energy decreases to zero when the truck stops, with the mechanical energy ultimately becoming internal energy within the truck.

Areas of Agreement / Disagreement

Participants express confusion regarding the conversion of mechanical energy and the role of static friction, indicating that multiple views remain on how energy is transferred and whether static friction contributes to energy loss.

Contextual Notes

There are unresolved questions about the assumptions regarding energy conversion and the definitions of work in the context of static friction. The discussion does not reach a consensus on these points.

physicsisgrea
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I know static friction can cause an object to accelerate, but also decelerate.
And i also know that static friction never cause energy loss, but I wonder when it causes an object to decelerate, its kinetic energy should decrease, so where is the mechanical energy gone? Has static friction done work on the object? Thank you!
 
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Please give a specific example of what you have in mind.

For example, a car slowing down. Assuming the tires do not slip, it is static friction from the ground that slows the car. (Ignoring air resistance, etc.) But that static friction does no work. The mechanical energy of the car has gone into internal energy within the car (the brake pads, for example).
 
My textbook says
When a box is placed on a traveling truck , and then the truck brakes to stop, the deceleration of the box is because of the static friction. (There is no sliping occurs)

I am confused because the box's K.E. should decrease to zero, and I have no idea how and where the mechanical energy is taken away. Is it converted into internal energy of the box?
 
physicsisgrea said:
My textbook says
When a box is placed on a traveling truck , and then the truck brakes to stop, the deceleration of the box is because of the static friction. (There is no sliping occurs)
OK.

I am confused because the box's K.E. should decrease to zero, and I have no idea how and where the mechanical energy is taken away. Is it converted into internal energy of the box?
The box's KE does go to zero when the truck stops. You can just think of the box and just another part of the truck. All of that mechanical energy ends up as internal energy within the truck.
 
Doc Al said:
OK.


The box's KE does go to zero when the truck stops. You can just think of the box and just another part of the truck. All of that mechanical energy ends up as internal energy within the truck.

Thank you so much !:)
 

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