1. Friction
01 January 2019 Objectives: To describe the causes and effects of frictional forces. Explain how a lubricant to reduce frictional forces.

2. Starter (5 mins)
Show the students a car performing a race lap and creating skid marks
Ask the students to explain how and why skid marks were produced.
Clip from top gear

3. Main
Demonstrate the effect of frictional forces by attempting to drag a large box across a smooth surface with a forcemeter.
Is the force making it easier or more difficult for the box to move?

4. What is friction?
If you rub your hands together, they get warm because there is resistance to the rubbing motion.
What is the name of this resistive force?
It is called friction.
What causes this force?
Your hands might look smooth, but on a microscopic level they have rough surfaces, as shown in the photograph.
Photo credit: © Martin Dohrn / Science Photo Library
When you rub your hands together you feel the resistive force of friction.

5. Friction and motion
Friction always tries to slow moving objects down – it opposes motion. Frictional forces occur when two touching surfaces move past each other, in this case the box moving across the ground.
pull of rope on box
friction
Friction also occurs when things move through air. This is called air resistance.
Friction is a contact force and only acts when a force is applied to an object.

6. What are the sources of friction?
Label all sources of friction acting on this bike.
pedal
bearing
air
resistance
links in
chain
brake pad
Photo credit: © 2008 Jupiterimages Corporation
tyre and
road
wheel
bearing

7. Friction is a force that opposes movement.
There is friction when an object moves over a solid surface.
There is also friction when something moves through a liquid or gas.
The rougher the surface the more friction there is

8. Surface
Amount of force (newtons)
Carpet
Wood
Sand paper
Material
Metal

9. 11.3 Friction 9

10. USES
PROBLEMS
Stopping things moving when they shouldn't.
Stopping things moving when the should.
Producing heat
Wears surfaces down, like shoes, tyres, carpets.
Allows you to walk
Producing heat.
Allows things to move along the ground.

11. Worksheet
Q1a-e

12. 11.3 Friction all around us
Why is it harder to stop a car on a wet road?

13. Streamlining

14. Lubricants
Lubricants are used to reduce friction.

15. Plenary
Students discuss their experimental results and present them in an appropriate format (graph)