# Static Friction Vs. Kinetic Friction: The Differences You Didn't Know

The comparison between static and kinetic friction, presented in this article, identifies the main points of difference between the two. Dry Friction, in all its forms, can be classified into these two main types.

Omkar Phatak

Last Updated: Mar 7, 2018

What is Friction?

Friction is the opposing, resistive force between two fluid, solid, or any material surfaces, that acts to hinder relative motion between them. It is always directed in opposition to the direction of motion. It is not a fundamental force of nature. It is a macroscopic force that emerges out of electromagnetic interactions between two surfaces, in contact with each other.

F ≤ μN

where 'μ' is the coefficient of friction and 'N' is the normal force between the two surfaces.

Differences Between the Two

Definition

Static friction is the frictional force that exists between two solid surfaces, that are non-moving. The lateral relative motion between these two surfaces, is stalled by the force of static friction. Due to it, there is no slipping and therefore, there is no motion.

Kinetic friction occurs between two moving solid surfaces, in contact with each other. Even though objects are in motion, the force of friction cannot be eliminated completely and it continues to be a resistive force to motion.

Kinetic friction occurs between two moving solid surfaces, in contact with each other. Even though objects are in motion, the force of friction cannot be eliminated completely and it continues to be a resistive force to motion.

Coefficient

The static and dynamic friction coefficients are two numbers that are calculated to get an estimate of dry friction, felt between two surfaces. Both ratios are calculated between the force of friction and the normal force felt between the two solid surfaces. The coefficient of static friction (μ) is given by:

F = μ

The strength of friction between two static surfaces can be estimated by calculating the coefficient of static friction.

Coefficient of kinetic friction is given by the equation:

F = μ

where μ

F = μ

_{static}NThe strength of friction between two static surfaces can be estimated by calculating the coefficient of static friction.

Coefficient of kinetic friction is given by the equation:

F = μ

_{kinetic}Nwhere μ

_{kinetic}is the coefficient of kinetic friction. The coefficient for the static variety is generally higher than the kinetic friction coefficient for two solid surfaces, in contact with each other.