A car is moving without sliding means that the friction between wheels and the ground is static friction. This is the force causing an object to move forward, therefore, its direction is the same as the moving direction of the car.
My question is: For the horizontal forces acting on any moving(without sliding) car, $\ F_{fs}$ always oriented forward, what's the backward force to balance $\ F_{fs}$ so as to keep the car moving uniformly? Is that the Force produced by engines?
Just to clarify, I am referring to auto cars (with engines).
Any help or thoughts are appreciated!!!
Best Answer
I agree that friction in the drive mechanism reduces thrust, rather than opposing the motion of the car. However, this is not the case for wheels which are not in the drivetrain - ie where there is front/rear wheel drive instead of 4-wheel drive. Friction in non-drivetrain wheel mechanisms are then sources of resistance to motion. If the car has rear-wheel drive, then the static friction on the rear wheels is forwards and the friction on the front wheels is backwards.
In both types of wheel there is also "rolling resistance" which is the net horizontal component of mostly vertical forces caused by deformation of the tyre.
https://en.wikipedia.org/wiki/Rolling_resistance