5.4 Starter 2 explained
07 October 2011
09:04
<<animation - why a drawing pin works.swf>>
· 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
5.4 Pressure Questions
07 October 2011
11:47
· PFY p.91, Q.3 and 7.
Pressure=Force/A
100000=F/10
100000*10=F
1 000 000N=F
A) P=F/A
P=500/5
P=100N/m2
B) F=P*A
F=100*20
F=2000N
1) Snow shoes have a large SA,
so there is less pressure
therefore they don’t sink in the snow when they walk
2) Large A
Less pressure
Enables them to go through mud without sinking/getting stuck
Also, as they are used on farms,
it enables them to roll over objects such as potholes easier without bursting a tire
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