People touch the ground when walking, and press the ground when pedaling. The friction between the foot and the ground is based on the ground, that is, the direction of pedaling is backward, that is, the foot tends to move backward, so the friction on the foot moves forward, and people move forward under the action of this force.

The four-step method for determining the friction direction is as follows:

1, the stressed object for which friction is found.

2. Select the applied force object as the reference object.

3. Judge the relative motion direction or relative motion trend direction of the stressed object.

4. Use "opposite" to determine the direction of friction.

Friction direction

The direction of friction, such as the circular motion of an object on a disk, is perpendicular to the direction of motion, but the direction of friction is opposite to the direction of relative motion between the object and the disk.

Friction is divided into static friction, rolling friction and sliding friction. When an object slides on the surface of another object, there is friction between the contact surfaces that hinders their relative movement. This friction is called sliding friction. Sliding friction is related to the roughness and pressure of the contact surface. The greater the pressure, the rougher the contact surface of the object and the greater the sliding friction.