# B Friction Force

Summary
Is there any friction force when we drive at a constant velocity?
Suppose we are driving on moon (I mean there is not air resistance) at a constant velocity. Suddenly the car goes on an icy land (the friction is zero). What happens?
In other words, if we drive at constant velocity and there isn't air resistance, Is there any friction force between tires and road? If yes, why?

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#### PeroK

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Summary: Is there any friction force when we drive at a constant velocity?

Suppose we are driving on moon (I mean there is not air resistance) at a constant velocity. Suddenly the car goes on an icy land (the friction is zero). What happens?
In other words, if we drive at constant velocity and there isn't air resistance, Is there any friction force between tires and road? If yes, why?
If a wheeled vehicle is neither braking nor accelerating, then there is negligible friction. Technically there is a "rolling resistance", which may be also small, and explains why rolling is so efficient. An object, wheel or ball, rolling on a smooth surfaces slows down gradually. Whereas, a flat object sliding on a surface tends to slow down under friction.

#### A.T.

...(the friction is zero)....Is there any friction ....

No, I only asked my question in two ways. Is there any friction force? and if no, so the car continues its straight route with no problem on an icy land.

#### Mister T

Gold Member
In other words, if we drive at constant velocity and there isn't air resistance, Is there any friction force between tires and road? If yes, why?
Yes. At the place where the tire makes contact with road there is deformation of both the tire and the road.

An object, wheel or ball, rolling on a smooth surfaces slows down gradually.
Are there any differences between a ball and the tire of a car, whereas the tires of car get their force from the engine?

Yes. At the place where the tire makes contact with road there is deformation of both the tire and the road.
Has the friction force the same direction as the car moving or is in the opposite?

#### hutchphd

In the absence of friction (but still with real dissipative tire flexion) the tire will rotationally decelerate but the car will maintain speed . The deceleration of the tire would be caused by differential vertical flexion, not "friction"

#### Nugatory

Mentor
Has the friction force the same direction as the car moving or is in the opposite?
You can work this out for yourself by considering that a car coasting without power will eventually come to a stop. Because it is coasting without power the only force acting on it will be friction (both rolling resistance and air resistance are forms of friction).
1) what are the initial and final speeds?
2) in view of the answer to #1, what is the change in velocity? (Be careful to get the sign right)
3) acceleration is defined to be the change in velocity over time. What direction is the acceleration?
4) what direction will the force point to produce acceleration in that direction?

"Friction Force"

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