1. What is todays lesson about?

2. 5.3 Friction: friend or foe 09 January 2011 Slip and slide on ice

3. 5.3 Friction: friend and foe!Starter question QFor each of these activities, decide whether friction is a good thing or a bad thing. For some, friction in one place might be good, but in another might be bad. 1 of 1

4. Aims Recognise that friction is a contact force. [Level 3] Identify when friction is useful and when it is not. [Level 4] Describe how friction can be reduced. [Level 4] Explainwhy grooves in tyres are important. [Level 6]

6. Friction and bicycles Friction is a force that acts when surfaces rub together It can be a useful force Friction between a bikes tyre’s and the road gives it grip When you apply your brakes, friction slows you down

8. Friction causes problems When two surfaces rub together you get friction One problem is that the parts are worn away Friction also creates heat which is often wasted energy To reduce friction we use lubricants such as oils and grease

9. What problems does friction cause?

11. Choosing the right tyre An F1 racing car comes smoothly round the last bend and down the final straight. Fans cheer as it passes the chequered flag. Friction between its tyres and the road gives it the grip it needs to take corners fast. There are several to choose from…

12. Wet tyres ‘Wet’ racing tyres have grooves cut into them like ordinary car tyres so they get rid of water, but they slow down the car

13. Dry tyres ‘Dry’ tyres have the most grip but cannot get rid of water when it rains

14. Intermediate tyres Intermediate tyres are in the middle. They can get rid of a little water and are faster than wet tyres on a damp track,

17. 5.3 Friction: friend and foe!Questions (Level 3) How can we reduce the amount of friction on moving parts? Copy and complete the sentences below using these words: brakes surfaces worn Friction is caused when two _______ rub together. It is useful when we want to use our _______. When two _______ rub together, frictioncauses them to be _______ down. (Level 3) 1 of 3

18. 5.3 Friction: friend and foe! Questions (Level 4) Why are you much more likely to crash when riding a bike on an icy day? Why do cars that go off-road have deeper grooves cut into their tyres than road cars? Why does a racing car with ‘wet’ tyres travel more slowly in dry weather than one with ‘dry’ tyres? If ‘dry’ tyres have few grooves and the most grip, why do you need to change tyres on road cars when the grooves are worn down? (Level 5) (Level 6) (Level 7) 2 of 3

19. 5.3 Friction: friend and foe! Questions (Level 7) You wake up in the morning and get up to go to school. What problems would you have if there were no friction? Write a short story about your problems. 3 of 3