# Question about static friction and energy loss

1. Jan 10, 2012

### physicsisgrea

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!

2. Jan 10, 2012

### Staff: Mentor

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).

3. Jan 10, 2012

### physicsisgrea

My textbook says
When a box is placed on a travelling 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?

4. Jan 10, 2012

### Staff: Mentor

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.

5. Jan 10, 2012

### physicsisgrea

Thank you so much !!:)