Physics Form 4 - Pressure

Concept Of Pressure

1. Pressure, P is define as the force acting normally per unit area.
2. Pressure is a scalar quantity and a derived quantity.
3. Pressure = Force/Area, P = F/A.
4. Where F = Force in newtons (N). 
5. A = Area in contact in square metres, m²   
6. The symbol of pressure is P.
7. The SI unit of pressure is the pascal (Pa). 
8. Non SI units used for measuring pressure include mm HG, mm air or atmosphere (atm).
9. Pressure increases when the surface area decreases.
10. Pressure increase when the acting force increases.

Applications Of Pressure

1. The strap of a handbag may be fixed with a piece of leather.
2. The piece of leather reduces the pressure acting on the shoulder by increasing the area of the handbag in contact with the shoulder.
3. A person lying on a plank fixed with a thousand nails will not feel painful.
4. If the person lies on a plank fixed with only a few nails, he will feel painful.
5. This is because the total area of the thousand nails in contact with the body is large and this reduces the pressure.
6. Cutting meat or vegetables is easier using a sharp knife compared to a blunt one. 
7. This is because the cutting edge of the knife has a very small area and produces a higher pressure. This makes the blade push through and cut easily.
8. Studs on the soles and heels of a pair of football boots have small areas in contact with the ground.
9. These produce high pressure to make the studs sink easily into the ground and give extra grip while running.