What Is Rolling Contact?

Rolling, Chinese vocabulary, is defined as the movement of a rotating body in the direction of rotation is called rolling. Also refers to the plane compound motion of rotation and displacement in physics.

Rolling : The movement of the rotating body in the direction of rotation is called rolling.

Technical terms .

Human walking is equivalent to rolling a polygon.

The walking of a person is similar to the movement of a person in a wheelchair. The rim is equivalent to a polygonal edge, the sacroiliac joint is equivalent to a wheel axle, the legs are equivalent to spokes, and the foot is equivalent to a polygonal edge.

The rear wheel of a bicycle is rolled by rotation, and the force at the point of contact with the ground is backward (opposite to the rolling direction). Therefore, the direction of the static friction force is the same as the rolling direction; the front wheel is the rolling force generated by the flat action force transmitted through the front axle, and the direction of the force at the contact point with the ground is forward. Therefore, the direction of the static friction force is backward.

When not pedaling, due to the inertia effect, the two wheels still maintain the original motion state, and the friction mode does not change. For example: take the rear wheel off the ground, shake the pedal, rotate the rear wheel, and then make it contact the ground, the bicycle will move forward. (This movement is equivalent to inertial rolling). You will find that the dust or small sand under the wheel is thrown backward, that is, the wheel has a backward force on the ground. Therefore, the direction of the force (friction) of the ground on the wheel is still forward.

When braking, the driving wheel (rear wheel) decelerates due to the increase in resistance torque, but the friction mode does not change; however, if the driving wheel is in a dead state, the friction between the driving wheel and the ground when the bicycle continues to move due to inertia It is sliding friction, and the front wheels are still static friction. ^[2]