Kinetic Friction & Force Vectors

[futuredoc31]

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Hey guys,

If a block at rest was pushed to the right by an external force on a surface with kinetic friction, I know that the horizontal component is to the right and the friction opposes this motion, which points to the left based on Newton's third law. What if you have a car that was moving to the right, what is the direction of the horizontal and friction forces?

I am confused because in a moving car, it uses internal forces to provide its motion where its wheels pushes against the surface and consequently frictional force of the road pushes back onto the car, thus causing it to move right. So shouldn't the horizontal component point to the left and friction point to the right? Also as a follow-up question, what happens to the direction of the forces if the car where to then apply the breaks?

 

[dechristine]

In a car moving to the right, the applied force points to the right and the friction opposes the motion, pointing to the left. The applied force has to point in the direction of motion, or else the car won't move in that direction. However, the friction pointing to the left causes the wheel to have a torque (spin) clockwise, which is why the car moves to the right.

 

[bionotes]

That is correct and just adding to what dechristine said, if there is no friction the car will slide like what happens on icy surface and static friction will point to left in this case as well. As a matter of fact in real word there is always a component of static friction but it is negligible in most cases.
Force of the friction is the one that is causing rotation of wheels.

 

[bionotes]

Sorry, please ignore part of my previous post. In case of moving surfaces there will not be any static friction component. So "As a matter of fact in real word there is always a component of static friction but it is negligible in most cases.
Force of the friction is the one that is causing rotation of wheels. " is WRONG