May 29, 2025 ☼ definition

Friction is a force of resistance.

It resists, or opposes, motion.

Static friction:

force that resists the sliding or rolling of one solid object over another when the two objects are at rest with respect to each other. Static friction | Britannica

Kinetic friction:

friction acting between objects in relative motion with respect to each other is called kinetic friction. Static friction | Britannica

Some frictional force is necessary, providing the traction needed for walking, for example, and keeping our furniture from sliding all over the place.

However, overcoming friction takes a lot of energy; a certain amount of energy must be expended to overcome friction in order to initiate or maintain movement.

How much friction = area of contact between the surfaces + the load/weight pressing those surfaces together:

First, the amount of friction is nearly independent of the area of contact. Second, friction is proportional to the load or weight that presses the surfaces together. Friction | Britannica

It’s always harder (more energy is required) to initiate movement than to continue movement:

Static friction, in contrast, acts between surfaces at rest with respect to each other. The value of static friction varies between zero and the smallest force needed to start motion. This smallest force required to start motion, or to overcome static friction, is always greater than the force required to continue the motion, or to overcome kinetic friction. Friction | Britannica