Force and Friction: Push, Slide and Stop
Understand that friction opposes motion, that static friction matches a push up to a limit, and that the net force (push minus friction) decides whether speed changes, with balanced forces meaning constant velocity, not necessarily rest.
Before you try
What if you pushed exactly as hard as friction pushes back? Would the block stop, or keep sliding for ever?
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What happened?
Move a control to see what changes and why.
Friction is modelled as one number per surface, and air resistance is ignored. Real surfaces vary from spot to spot.
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Try these ideas
- On wood, raise the push slowly and find the exact force where the block breaks free.
- Once it is sliding, lower the push until the speed stops changing. What is the net force then?
- Try the same push on ice and on the rubber mat and compare the accelerations.
Why it works
Friction is the force between two surfaces that resists sliding. Before a block moves, static friction grows to match your push, up to a limit set by the surface (its coefficient, μs) and how hard the block presses down (its weight, m × g). Once the block slides, friction drops to a slightly smaller kinetic value, μk × m × g. The difference between your push and friction is the net force, and net force divided by mass gives the acceleration.
In this simulator you set the push, the mass and the floor, then press play. Arrows show the push, friction and net force with their values, a trace records the speed, and the state card names what is happening. The floor coefficients stay fixed, gravity is 9.8 m/s² and there is no air resistance.
Check your understanding
Question 1 of 4
A block slides at a steady 2 m/s while you push it. What is the net force on it?
Balanced forces on an object mean it must be…
You push a 10 kg block on wood (μs = 0.4) with 30 N and it does not move. How big is friction?
You stop pushing a sliding block. What does friction do?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
What will you discover next?
Try Kinetic and Potential Energy: Build a Coaster next.
For parents & teachers
- Ask why it is harder to start pushing a heavy box than to keep it moving.
- Discuss why cars need longer to stop on icy roads.
- Find three places at home where friction is useful and three where it is a nuisance.