5.3 Friction: friend or foe09 January 2011

Q For 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.

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5.3 Friction: friend and foe!

Starter question

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]

• Explain why grooves in tyres are important. [Level 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

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

What problems does friction cause?

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…

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

Dry tyres

• ‘Dry’ tyres have the

most grip but

cannot get rid of

water when it rains

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,

5.3 Friction: friend and foe!Questions

1. How can we reduce the amount of friction on moving parts?

2. 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, friction causes them to be _______ down.

(Level 3)

(Level 3)

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5.3 Friction: friend and foe! Questions

3. Why are you much more likely to crash when riding a bike on an icy day?

4. Why do cars that go off-road have deeper grooves cut into their tyres than road cars?

5. Why does a racing car with ‘wet’ tyres travel more slowly in dry weather than one with ‘dry’ tyres?

6. 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 4)

(Level 5)

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(Level 6)

(Level 7)

5.3 Friction: friend and foe! Questions

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.

(Level 7)

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