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.