a car is travelling along a level road at constant velocity(that is its speed and direction are not changing draw a labled diagaram to show the forces that act on the car)
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Answer:
When a car is traveling along a level road at constant speed, the force of friction of the road on the tires in the direction it is traveling is exactly equal to any forces that would otherwise cause the car to slow down - like air resistance as well as ‘rolling’ resistance (which is not actually a friction force but due to distortion in the tires). That is, to travel at constant speed, there can be no net force on an object. So if there are resistive forces, one must look for a force acting on the car that would allow it to maintain constant speed. The only ‘object’ that is acting on the car in the forward direction is the road. And that force is friction between the pavement and the tires.
As you can see from this, friction is really subtle. We normally think of friction as always opposing the motion of an object. But that is not necessarily so. For example, if the car slammed on its brakes, the friction of the pavement on the tires would definitely slow the car - that is, that force would be opposite the direction of travel. But if it is accelerating forward, that is the force that accelerates it. (Note: The engine does not act on the car, it is part of the car - and an object cannot exert a force on itself. The engine and drive train and wheels conspire to push against the road - and the road pushes back. And that is the force that accelerates the car.) So if the car is traveling at constant speed, that frictional force forward must be sufficient to maintain that speed even though there are resistive forces that would otherwise slow it down.
Explanation: