Objective 5.4

5.4 Starter

07 October 2011

11:46
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5.4 Starter 2 explained

07 October 2011

09:04

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· Your finger pushes on the pin and the pin pushes back on your finger
· N3L tells us that all these two forces are equal in size
· The pin pushes on the wall and the wall pushes back on the pin
· N3L tells us that all these two forces are also equal in size
· If the surface area is large then the force is spread over a large area and the pressure is low
· If the surface area is small then the force is spread over a small area and the pressure is high
· You would like the pressure on your finger to be low and the pressure on the wall to be high
· The other way round is painful!

5.4

07 October 2011

10:37
· 5.4 recall and use the relationship between pressure, force and area:

pressure = force / area

p = F / A

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5.4 Pressure Questions

07 October 2011

11:47
· PFY p.91, Q.3 and 7.

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3) p=F/A 100,000N=F/10 100,000 x 10 = 1,000,000 N

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7a) p=F/A p= 500/5 P= 100N/ cm2

b) p= F/A 100= F/20 P= 2000N

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Question 1) Inuits wear snow shoes because if you look at the relationship between p=F/A when the area decreases the pressure increases. for example- 12/6 (area) = 2 (pressure) but 12/3 (area) =4 (pressure)

So if there is a large surface area on the snow shoes the Inuits will not sink into the snow.

Question 2) Tractors have big tires because p= F/A. when the area increases the pressure decreases. If the tractors have small tires the pressure will increase and the tractor will sink into the ground.

animation - why a drawing pin works.swf Download this file