Friction and drag
Friction can be a help or a nuisance.
Helpful
friction
Walking or running
Brake blocks on a bike and the rim of the
bike wheel
Soles on your shoes
Disc brakes on a car.
Cornering in a car or on
a bike
Friction between the tyres and the road
Friction keeping knots in shoelaces
or string tied together.
Air brakes for aircraft and in parachutes
Gloves for catching
balls and goalkeeping
Sandpaper
Problems with friction
In all moving parts in machinery
making heat
Spacecraft re-entering the Earth's atmosphere making heat
Friction
between an aircraft and the air making heat
Friction between a boat and the
water
Friction between a car and the road making a static electric charge
Friction
causing car tyres to become bald
Reducing
friction
Engineers always try to make the friction in their machines less to
make them more efficient.
They do this by putting something between the parts to stop
them rubbing together. They can use:
(i)
oil
(ii) ball bearings
(iii) rollers
(iv) a gas
The two surfaces are kept apart
by:
(a) blowing air between them (hovercraft)
(b) using strong magnets to push them
apart
Air friction is made less by streamlining the object.
Cars are designed to
give low drag and speed skaters wear tight fitting suits to reduce air
friction
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