Teacher sheet · Ages 10–11 · about 45–50 minutes
Friction: the force against motion
Lesson page: echoesof.science/school/friction/ages-10-11/ · Pupil worksheet: echoesof.science/school/friction/ages-10-11/print/
Learning aims
- Friction acts between surfaces in contact, opposite to the motion.
- Static friction is usually greater than kinetic friction.
- Friction depends on the materials and can be reduced by lubricants and wheels.
- Use a force meter and carry out a fair test with repeats.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: push a heavy bag of books along the floor. When is it hardest? |
| 10 min | Read the text; look at sandpaper and shoe soles as models of rough surfaces. |
| 20 min | Force meter fair test in groups. |
| 5 min | Play More friction or less? |
| 5 min | Quiz and compare the class results. |
Materials for the experiment
- A force meter (newton meter, 0–10 N)
- A shoe or a small box with a hook or string
- Some weights or books to put in the box (always the same)
- Different surfaces: table top, carpet, sandpaper sheet, kitchen foil, a towel
Safety: Pull gently; don't let the force meter snap back. Keep sandpaper on the table and wash hands after touching it. Don't use heavy loads.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Friction only happens when things move. | Static friction acts even before anything slides. |
| Smooth surfaces have no friction. | All surfaces are rough close up, and molecules can stick together. |
| Friction is always a nuisance. | We need it to walk, grip, and brake. |
Worksheet answers
- Pull arrow pointing right; friction arrow pointing left, along the surface.
- Static friction (before sliding) is bigger than kinetic friction (while sliding), so a bigger force is needed to start.
- Changed: the surface. Measured: the force on the force meter. Kept the same: shoe or box, load, speed, force meter.
- Useful: shoes gripping, bike brakes. Reduced: oil on a bike chain, wheels on a suitcase, waxed skis.
Quiz answers
- In which direction does friction act? Opposite to the motion. Friction acts opposite to the direction of motion.[3][1]
- Which needs a bigger force? Starting a box sliding. Static friction is usually greater than kinetic friction.[2][1]
- What does a lubricant such as oil do? Reduces friction. Lubricants reduce friction.[3]
- Why do we put wheels on heavy things? Rolling friction is much smaller than sliding friction. Sliding friction is about 100 to 1,000 times greater than rolling friction.[2]
- Where does the energy go when friction slows down a car? It turns into heat. Friction turns kinetic energy into thermal energy.[5]
- Which grips best? Rubber on dry concrete. Rubber on dry concrete has the highest coefficient of these.[1]
Going further
Put the box on its side so a smaller face touches the table, with the same load. Does the force change? (Most of the time it hardly does: friction is nearly independent of the contact area.)
Sources used in this lesson
- [1] University Physics Volume 1, 6.2 Friction (OpenStax, Rice University): reliability High
- [2] Friction (Encyclopaedia Britannica): reliability High
- [3] Friction (Science Continuum F–10) (Victorian Department of Education (Australia)): reliability High
- [5] College Physics 2e, 7.5 Nonconservative Forces (OpenStax, Rice University): reliability High
- [7] What is Drag? (NASA Glenn Research Center, Beginner's Guide to Aeronautics): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/friction/sources/
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