Calculation of Pressure
Pressure is the force per unit area over which the force is applied. It is a scalar quantity.
Formula for Pressure
Pressure is a measure of the force applied per unit area.
The symbol P indicates pressure. It is usually measured in Pascals (Pa) or Newton/metre2.
The pressure exerted on an object depends on the applied force and area. Pressure is inversely proportional to area. For example, a sharp knife cuts well than a blunt knife. A sharp knife blade has a small surface area, so it exerts high pressure to easily cut the object. If both force and pressure are doubled, the area remains the same.
Formula Triangle : Pressure, Force and Area
Example 1: A wooden box weighs 10 N, and its base has an area of 0.8 m2. What is the pressure exerted by the box on the floor?
Answer: Pressure = Force/Area
= 10 / 0.8
= 12.5 Pa or 12.5 N/m2
The pressure exerted by the box on the floor is 12.5 Pa or 12.5 N/m2.
Example 2: A woman applies 200 Pa of pressure with her hand on a door. Her hand has an area of 0.03m2. Find out the force being applied.
Answer: Pressure = Force/Area
Force = Pressure x Area
= 200 x 0.03 = 6 N
The force applied by the woman is 6N.
Example 3: A skier weighs 480 N and exerts a pressure of 2,400 Pa on the snow. What is the area of the skis?
Answer: Pressure = Force/Area
Area = Force/Pressure
= 480 / 2400
= 0.2 m2
The area of the skis is 0.2m2
Atmospheric Pressure
Atmospheric pressure is around us all the time. It decreases with increasing altitude.
As we go higher, the density of
air reduces. As you move up through the layers of the atmosphere, there are
fewer air molecules in the air. Therefore, atmospheric pressure decreases due
to fewer air molecules. The pressure at sea level is higher than at the top of
Mount Everest.
Pressure in Liquids
When an object is placed in water, it experiences water pressure from all directions. In liquids, the pressure at a point is created by the weight of the liquid. As you dive deeper into a body of water, more weight is pushed down due to more water at the top. That's why water pressure increases with depth.
When immersed in liquid, the body creates an upward force called upthrust. The upthrust force equals the weight of the fluid displaced by the object. An object (like a boat) will float on the water if its weight equals the upthrust. It will sink into the water if its weight exceeds the upthrust.