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Physic Form 4 : Chapter 3

Force and Pressure

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Understanding Pressure

Pressure is the force which acts normal per unit area ofcontact.It's perpendicular force that acts on a unit area.

Formula

Pressure,P(Nm-2/Pa) = Force,F(N)

Area,A(m2

)

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Factors that affect the pressure acting on a surface For a fixed force, smaller contact area will produce greater

pressure.

For a fixed contact area,larger force will produce greaterpressure.

Stilettos will cause most pain when it tread on ourfoot.This is because, stilettos has the smallest area ofcontact with our foot.So,stilettos will exert the most

pressure on our foot...

Sneakers cause less pain when it tread on our foot.This isbecause, sneakers has bigger area of contact with ourfoot.So,sneakers will exert less pressure on our foot...

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Example question :

The wind force on the wall is 1600N.If the wall has an area of

8m2,what is the pressure on it?

Pressure,P(Nm-2/Pa) = Force,F(N)Area,A(m2)

So, Pressure = 1600N8m2

= 200Pa

So,wind pressure on the wall is 200Pa

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Formula

where :P = Pressure

h = depth

= density of liquid

g = Gravitational Field Strength

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The jet of water is further than the jet of oil fromthe similar holes at the same height.

This is because the density of water is higherthan oil and hence,the pressure of the water isalso higher than the oil