The basic principle is as follows: Under the same conditions, the rolling friction coefficient is the smallest. Rolling friction When an object rolls or tends to roll on the surface of another object without sliding, it is called "rolling friction" because the two objects are deformed by pressure at the contact part. Its essence is static friction.

Due to the deformation of the contact between the object and the plane, the object is trapped in the bearing surface under the action of gravity, and the object itself is compressed and deformed. When the object rolls forward, the bearing surface in front of the contact point bulges, so that the acting point of the synthetic elastic force n acting on the object by the bearing surface moves forward from the lowest point.

It is this elastic force that produces a moment that prevents the object from rolling relative to the center of mass, which is rolling friction. For junior high school students, there is no concept of mastering torque, so don't regard rolling friction as a kind of friction, just talk about the obstacles to rolling when one object rolls on another.

Extended data:

The rolling of an object is related to the contact surface. When a rolling object rolls or tends to roll on the contact surface, both the object and the contact surface will be deformed.

Its deformation can be divided into four situations: the contact surface is deformed and the rolling body is not deformed (the object is called a rigid body at this time), the contact surface is not deformed and the rolling body is not deformed (the contact surface is called a rigid surface at this time), the contact surface and the rolling body are not deformed, and both the contact surface and the rolling body are deformed.

The rolling object is rigid and the contact surface is deformed.

The gravity g and supporting force n of a rolling object resting on a horizontal contact surface are on the same vertical line. When the rolling object rolls forward, it interacts with the front projection, the fulcrum moves forward to O', and the force on the contact surface increases to N'. N' produces two effects: one is N perpendicular to the direction of contact surface, which competes with G; The other is the static friction force F along the contact surface, which prevents the ball from sliding forward, as shown in Figure 3.

force of rolling friction

Obviously, gravity G and supporting force N produce a couple moment M resistance, which is used to hinder the rotation of the object. Let the distance of O' deviating from the gravity line be δ, then M resistance =Nδ.

If the vertical distance from the component f of n' along the contact surface direction to O is R, and O is taken as the rotation axis, when the object rolls at a uniform speed, fr=Nδ.

When rolling soil subgrade, the roller of roller can be simplified as this kind of problem.

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