Force & friction simulator
Push a block across a level floor and see exactly when static friction gives way. On a horizontal surface the normal force is N = mg, so the maximum static friction is fₛ = μₛmg and the kinetic friction on a sliding block is fₖ = μₖmg. A push larger than the limit produces a net force and an acceleration a = (F − fₖ)/m.
What if you changed…
Find the smallest push that overcomes static friction.
See the calculation
- 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.
What this model assumes
Horizontal surface, rightward applied force, g = 9.81 m/s². For comparison, static and kinetic coefficients both equal μ. The block starts at rest.
Keep an eye on this
Static friction is not always μsN. That expression gives its maximum value.
Understand the physics ↗Formulas used in this simulation
- Normal force on a level surface
- N = mg
- No vertical acceleration
- Static friction
- fₛ ≤ μₛN
- Matches the push up to this limit
- Kinetic friction
- fₖ = μₖN
- Opposes the sliding motion
- Friction on level ground
- f = μmg
- Shortcut when N = mg
- Newton’s second law
- Fnet = ma
- Once sliding, a = (F − fₖ)/m
Force & friction: common questions
Wondering about the why? Start here.
What does fs mean in physics?
fₛ is the static friction force: the friction that stops a resting object from sliding. It matches the applied force up to a maximum of μₛN. fₖ is kinetic friction, which acts once the object is sliding.
Why is friction equal to μmg?
Friction equals μ times the normal force N. On a level surface where only gravity and the floor act vertically, N = mg, so f = μmg. On a slope or with an angled push, N is different.
What is the coefficient of friction μ?
A dimensionless number describing how strongly two surfaces grip. Values below about 0.1 are slippery, while 0.5 to 1 grip strongly. Static coefficients are usually a little larger than kinetic ones.
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.