Home / Topics / Newton's Laws & Forces
Static friction
Beginner
Friction that prevents sliding, up to a maximum value.
f_s ≤ μ_s NStatic friction opposes impending sliding and adjusts up to a maximum fs,max = μₛN. Below that value it exactly balances the applied force parallel to the surface.
A 10 kg crate with μₛ = 0.4 needs more than 39 N to start moving.
Static friction is not always μN; it equals the applied force until it reaches the limit.
In more detail
Static friction prevents an object from starting to slide. It adjusts to match the applied force up to a maximum value, equal to the coefficient of static friction times the normal force.
Real-world uses
- Shoes grip the floor because of static friction, allowing you to walk.
- Car tyres rely on static friction to avoid skidding when accelerating.
- A heavy box on a warehouse floor stays still until the push is large enough to overcome static friction.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why does friction sometimes help?
Static friction provides the force that moves you forward when you walk or a car accelerates.
Does static friction depend on contact area?
In the simple model, no. The maximum depends only on the normal force and the coefficient.
Is static friction always equal to μN?
No. Static friction takes any value up to μN, just enough to balance the applied force.
Related topics in Newton's Laws & Forces
Elevator problems · Pulley systems · Motion on an inclined plane · Kinetic friction · Angle of friction and repose · Rolling friction