# Will friction on tyres due to road still act if the vehicle is moving with constant velocity?

A car moves with the help of friction from ground...while analyzing a car moving with constant velocity..should one consider the frictional force acting at the contact point of road and wheel? If friction is acting..then how is the vehicle moving with constant velocity? If no, how is the body moving at all?

• Free body diagram. Always begin with a free body diagram. If it's constant velocity it means the FBD is going to show net zero force, not that any individual force is zero. Commented Jul 12, 2019 at 15:30
• Not clear if you're talking about a car free-wheeling (engine off) or being driven (engine running and gear engaged). Which? Commented Jul 16, 2019 at 8:48

An object will continue with the same velocity if the net force acting on it is 0.

The friction between the tires and the road is not the only force acting in this system. You also need to account for the other forces acting on the body, such as air drag and rolling resistance.

There is no need to analyse the friction acting on the vehicle.

Friction will actually act on the wheel...if not the wheel tends to slip and the vehicle will never move.....it is because of friction that all vehicles are able to move on roads without slipping..

Yes the vehicle can move with constant velocity though friction acts upon it....

consider a practicme example where your riding in a car.... you maintain a constant velocity... now if friction dosnt act on the wheels.....your vehicle shouldn't move....but it still moves right?....

On a rainy day even if you accelarate your vehicle ...the wheels tend to skid because the friction between the road and wheels is reduced by the rain water(this is best experienced when taking turns).....

Just because the system accelerates that dosnt mean friction is acting on the wheels and just because the system moves with constant velocity it dosnt mean there is no friction.

Sory the answer is a bit long....i wanted to make it a bit clearer

• If anyone spots something wrong in my answer please let me know so i can correct it. Commented Jul 12, 2019 at 15:49
• If a body is at rest..it is due to static friction...but we do not consider the frictional force in its fbd..don't know, I never saw anything like that in any book. Commented Jul 12, 2019 at 15:56
• I don't understand all the dots.... What do they mean...? A full-stop ends a sentence. Use a comma, like this, if you have something to interject. Commented Jul 16, 2019 at 8:47
• Im a bit used to it.It means nothing.Sorry😅 Commented Jul 16, 2019 at 9:43
• If a body is at rest,it is due to static friction.But we do not consider the frictional force in its fbd,don't know, I never saw anything like that in any book. Commented Jul 17, 2019 at 8:04

Friction will not act on the wheels of the car if we consider the ideal case of the wheels not getting compressed while the car is moving. This is because friction acts so as to prevent relative motion along the surfaces. As the wheels are rotating, there is centripetal acceleration of the point of contact of the wheels and the road which ensures that there can be no relative motion and hence no friction.

A car moves with the help of friction from ground

A car changes velocity with the help of friction from ground. It can (continue) to move just fine without any friction.

True if you start from rest, you will find it hard to get moving. But if we assume the car has already started moving, it doesn't come to a stop just because friction disappears. (Think of driving onto an icy lake)

If friction is acting..then how is the vehicle moving with constant velocity?

Constant velocity always means the same thing: zero net force. If there is a frictional force present, then there must be some other force that opposes it.

If no, how is the body moving at all?

Forces don't cause motion, they cause change in motion.

• What is that some other force,in a moving car? Commented Jul 16, 2019 at 6:18
• That depends on the situation. In a physics 101 question, there may be no other such force. It could be drag, in which case the tires (via the engine) need to supply a force to keep the car at a constant speed. It could be a strong tailwind and the car has to use the tires (and the brakes) to maintain a constant speed. Commented Jul 16, 2019 at 7:19