# Car moving at constant velocity.

As I understand it, friction is the force that accelerates cars on a road. Assuming that the car moves at a constant velocity, there is no net force on the car. But in this case, if friction acts to accelerate the car, what force acts to retard the car's motion? Surely it can't be purely the wind resistance as that would depend solely on the vehicles speed, and would not necessarily cancel out the forward fricitional force.

As I understand it, friction is the force that accelerates cars on a road. Assuming that the car moves at a constant velocity, there is no net force on the car. But in this case, if friction acts to accelerate the car, what force acts to retard the car's motion? Surely it can't be purely the wind resistance as that would depend solely on the vehicles speed, and would not necessarily cancel out the forward fricitional force.

The resistance in addition to wind would be mechanical drag, hysteresis of the tires, and so forth.

In other words, the car has to overcome the resistance of the drive train rotation, meshing gears, spinning a flywheel up to speed, rolling resistance of the tires, brake drag, mechanical losses to drive accessory belts, etc.

I most probely am reading your question wrong, also I am not a Physicist. Other than the Air.

The rubber wheels on the tarmac, bearings and all the other moving parts on the car, then you have gravity.

Wayne

Rolling resistance (which is different than static friction) and aerodyanmic drag.
Thanks. That really cleared it out for me.