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# Pressure

## Definition of Pressure

"Thrust per unit area" OR "Force acting on an unit area of surface".

#### More About Pressure:

• Thrust is the perpendicular force acting on a body.
• Pressure is the ratio of Force to the Area over which that force is distributed.
• The S.I. unit of Pressure is the "PASCAL"
• Pressure is a scalar quantity, it has no direction.
• When the area is small, a moderate force can create a very large pressure. This is why a sharp knife is good at cutting things: when you push the very small area of the sharp blade against something, it creates a really large pressure.

#### Examples of Pressure:

• The studs on a foot ball boot have only a small area of contact with the ground. The pressure under the studs is high enough for them to sink into the ground, which gives extra grip.
• The area under the edge of a knife�s blade is extremely small. Beneath it, the pressure is high enough for the blade to push easily through the material.
• Tractors that have to work on soft ground are fitted with wide tyres. Larger area of tyres reduces the pressure and will not sink into ground.

#### Solved Example on Pressure

A small table weighing 40N stands on four legs, each is having an area of 0.001m2. What is the pressure of the table on the floor?
A. 400N/m2
B. 1000N/m2
C. 10 000N/m2
D. 40 000N/m2
Correct Answer is D.

#### Solution

Step 1: Write down the formula for pressure p = F/A
Step 2: Area = Area of 4 legs of table = 4 x 0.001 = 0.004m2
Step 3: Force = 40 N
Step 4: Applying the known values in the formula p = 40 / 0.004 = 40 000N/m2

Related Terms: Liquid pressure | Atmospheric pressure | Pascal�s law | Boyle�s law | Bernoulli�s principle.
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