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Forces & Friction Worksheet
By the end you will: tell static from sliding friction, find the net force and acceleration, and explain how friction can be reduced.
A. Explore with the simulation
Set the box mass to 20 kg. For each surface, raise your push slowly from 0 until the box just starts to move.
Surface Push needed to start it (N) Ice Wood Carpet Sandpaper On Wood with 20 kg, push with 120 N. Record the friction, the net force and the acceleration once it slides.
Push a 20 kg box on wood with 50 N. It doesn't move. What is the friction force? Are the forces balanced?
Put the box on wheels. How big is the push needed now?
B. Calculate (then check in the simulation)
A 50 kg box sits on carpet (static coefficient 0.8). What push starts it moving? (g = 9.8 m/sĀ²)
The same box slides on carpet (sliding coefficient 0.6) with a 400 N push. Find its acceleration.
A box moves at a steady 1 m/s while you push with 60 N. What is the friction force? Why?
C. Think it through
Give two ways friction helps us and two ways we reduce it.
Answer key (for teachers and parents)
- Ice: 20 N Ā· Wood: 98 N Ā· Carpet: 157 N Ā· Sandpaper: 196 N. Rougher surfaces grip harder.
- Friction 59 N (sliding), net force 61 N, acceleration about 3.06 m/sĀ² (= 61 Ć· 20).
- Friction is 50 N, exactly matching the push, so the forces are balanced and the box stays still.
- About 4 N, instead of 98 N on wood: rolling friction is far smaller than sliding friction.
- Max static friction = 0.8 Ć 50 Ć 9.8 = 392 N. A push just over 392 N starts it.
- Friction = 0.6 Ć 50 Ć 9.8 = 294 N. Net = 400 ā 294 = 106 N. a = 106 Ć· 50 ā 2.1 m/sĀ².
- 60 N. Steady speed means no acceleration, so the forces are balanced.
- Helps: walking without slipping, brakes stopping a cycle, writing with a pencil. Reduce: wheels and ball bearings, oil or grease, smooth polished surfaces, streamlined shapes.
Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/forces-friction.