Content: All objects always remain at rest or move in a straight line at a uniform speed when no force is acted upon.

Based on a large number of empirical facts, generalized through further reasonable reasoning

All objects have inertia at any time, and inertia is a property of objects

only about quality

Inertia only has magnitude, no direction

use

precaution

① Place the car on a smooth horizontal surface and keep it still

②Add weights to the pallets hanging on both sides of the trolley

③Add unequal weights on both sides and observe the phenomenon

④Add weights with the same mass on both sides and observe the phenomenon

Parallel to the contact surface of the object and opposite to the direction of relative motion (trend) of the object

Two objects are in contact with each other and have pressure

Rough contact surface

There is relative motion or a tendency of relative motion between two objects

① Prepare experimental equipment: three identical wooden blocks, ① ② place them on the wooden board, ③ place them on sandpaper; ② put weights on them; install the same three spring dynamometers on the three wooden blocks

①②: The greater the pressure on the contact surface, the greater the sliding friction.

①③: The greater the roughness of the contact surface, the greater the sliding friction.

Patterns on the soles and tires of running shoes increase friction with the ground

Apply anti-slip powder on hands before pull-ups and gymnastics exercises

When the machine is working, the friction of the moving parts will cause wear and tear. Try to reduce the friction.

Sweeping the ice during curling to reduce the roughness of the ice surface