20040 AC Science Year 4 Physical sciences
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What is friction? - I<br />
Read the text.<br />
Friction is an invisible force that exists between an object and the surface it moves<br />
along. It makes it difficult for an object to move across the surface because it<br />
works against the forces producing movement. Friction is a direct contact force<br />
that resists and reduces the speed of motion.<br />
The amount of friction depends<br />
on the force pressing the two<br />
I<br />
surfaces together and the type of<br />
surface. Some surfaces produce _<br />
little or no friction and an object<br />
will move quite easily for some<br />
distance across it. A bowling<br />
ball will, for example, travel very<br />
smoothly along the polished<br />
floor of a bowling lone. But other<br />
surfaces may produce so much<br />
friction that an object needs a<br />
very big force to move it and it<br />
may only travel a short distance<br />
before friction stops it again.<br />
The bowling boll, for example,<br />
wouldn't travel as quickly or as<br />
for across a floor with thick carpet on it.<br />
=========<br />
Friction affects many things we do in our everyday lives. It con help us and make<br />
things easier or it can make things we do more difficult. Simple activities like<br />
walking and writing would be impossible without friction holding our shoes to the<br />
ground and keeping a pencil in our hand.<br />
Think about a car rolling along a rood without its engine running. The friction<br />
between the car's tyres and the road will eventually cause it to stop. If the car<br />
had smooth tyres and the road was smooth too, it would travel further than it<br />
would if the tyres and the road were rough. Drivers choose the type of tyres<br />
they put on their cars to suit the roods they travel on. If their tyres didn't provide<br />
enough friction, they would slide all over the road when trying to stop. However a<br />
disadvantage that affects motorists is their cars waste energy by using extra fuel<br />
to drive against the force of friction. Aircraft also waste energy because of friction<br />
caused by air resistance, as do ships because of friction with water.<br />
When choosing footwear, people who play particular sports have to consider the<br />
amount of friction they'll need to ploy their sport. For example, footballers need<br />
studs on their boots for added friction to stop them sliding around, especially on<br />
wet grass. But a disadvantage for them is that the friction they need causes heat<br />
and wear and tear on their boots and they need to replace them regularly.<br />
R.I.C. Publications ® www.ricpublications.com.au<br />
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AUSTRALIAN<br />
CURRICULUM SCIENCE (<strong>Year</strong> 4)
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