# why is rolling friction less than sliding friction?

Hi,
Let us first understand the term “Friction”.
Friction is the force that resists the motion of one surface relative to another with which it is in contact. Therefore, friction is a force which resists the relative motion between the two surfaces in contact.

When we slide an object over another, there is friction acting between the two surfaces which reduces the relative velocity between the two surfaces during sliding. Now, if we somehow reduce the area of contact between the two surfaces then we can reduce the effect of friction between the two surfaces drastically.

Ideally, a body like a ring or a sphere rolling without slipping over a horizontal plane will suffer no friction. At every instant, there is just one point of contact between the body and the plane and this point has no motion relative to the plane. In this ideal situation, kinetic or static friction is zero and the body should continue to roll with constant velocity. We know, in practice, this will not happen and some resistance to the motion (rolling friction) does occur, i.e. to keep the body rolling, some applied force is needed but this friction (rolling friction) is much less than the sliding friction. This is the reason why for the same weight, rolling friction is much smaller than static or sliding friction.

Hope this helps,
Good luck.

• 0

I assume that  in sliding friction, an object is dragged over the ground, and the object is therefore moving in relation to the ground. The surface area of the underside of the object is in constant contact and motion with respect to the ground, and it is this underside surface dragging along the ground that creates the friction.

In a wheeled arrangement, the surface area of the wheel is stationary with respect to the ground - it does not drag along the ground, except in cases of skidding. As the wheel rotates, the adjacent surface area of the wheel comes into momentary stationary contact with the ground as the former surface area lifts up off the ground. Therefore, there is no dragging, and no energy lost due to friction between the wheel and the ground. In an automobile wheel, there is momentary deformation of the tire, which results in minor internal friction, but that friction is insignificant compared to the friction caused by dragging an object over the ground.

You know, if you imagine a round object rolling ove a surface, then if you see the cirle; which is a set of infinitely many equidistant points, at a given point of time, there is only on point coming in contact with the surface.    Hope this helps you out. Good luck.

• 6

Because it  comes in contact with less surface. I.e f is directly proportional frictional coffecient.

• 3

u r  cool

• -2

it is easier 2 roll an object than 2 slide it

• -1

Oh, thanks a ton! :)

• 1
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