Force & friction, explained.
Static friction adjusts to oppose a push, up to μsN. If the push exceeds that limit, the block begins to slide. Kinetic friction then acts against sliding motion. On this level surface with no vertical acceleration, N = mg.
The relationship to remember
A worked example
For a 5 kg block with μ = 0.3, the static-friction limit is 14.715 N. A 20 N push produces 5.285 N net force and acceleration 1.057 m/s².
Inside the default experiment
- Normal force N = mg = 5 × 9.81 = 49.05 N.
- Maximum static friction = μN = 14.71 N. Actual opposing friction = 14.71 N.
- Net force = 20 − 14.71 = 5.29 N. Acceleration = Fnet/m = 1.06 m/s².
When this model applies
Horizontal surface, rightward applied force, g = 9.81 m/s². For comparison, static and kinetic coefficients both equal μ. The block starts at rest.
Make a prediction. Then test it.
Find the smallest push that overcomes static friction.
Try the interactive experiment ↗Frequently asked questions
Wondering about the why? Start here.
Why is the block not moving with a small force?
Static friction balances the applied force while the force is at or below its maximum. The net horizontal force is then zero.
Why do the force arrows use the same scale?
A shared arrow scale lets you compare opposing forces. Equal arrows mean zero net force; their difference determines acceleration.