Pressure is defined as the force acting perpendicularly per unit area.
Pressure is a very important concept in physics and in everyday life. For example, when you press a thumbtack onto a notice board, the sharp tip makes it easy to push in because the force is concentrated on a very small area, creating high pressure. It would be more difficult to push a blunt pin through the same board. Consider the diagram below.
We experience pressure all the time around us. When you stand on the ground, your weight exerts pressure on the floor.
If you wear shoes with very thin heels, they exert more pressure on the ground than flat shoes because the area in contact with the ground is smaller.
In the figure above, the sharp pointed heels dig deeper on soft ground because the weight of the body acts on a small area.
Similarly, heavy vehicles use wide tires to spread their weight over a larger area and reduce pressure on the road. The pressure on each tire supports the weight of the vehicle. see the diagram below.
Pressure also exists in liquids and gases. Air around us exerts atmospheric pressure, which is why drinking through a straw works—the pressure outside pushes the liquid up the straw. Water pressure increases as you go deeper in a swimming pool or the ocean because the weight of the water above pushes downwards. This helps us explain many real-life phenomena, such as why dams are thicker at the bottom, why submarines are built with strong walls, and how hydraulic machines work.
By studying pressure, you will learn how force, area, and fluids interact, and how these ideas are applied in science, engineering, and daily life
Calculating pressure
pressure is the force applied on a surface divided by the area over which the force acts. This means that the same force can produce different effects depending on how spread out it is.
The SI unit of pressure is derived from that of force and area.
The SI unit of pressure is thus newton per square metre(Nm-2).
Newton per square metre is also know as the Pascal(Pa).
1 Nm-2 = 1 Pa
Some other units can be used to measure and express pressure. This is based on the height of liquid column that a given pressure can support.
This units includes: mmHg, cmHg and atmosphere.
mmHg means millimeter of mercury. It represents the height in millimeters of mercury that a given pressure can support.
Mercury is widely used in pressure measurements because of it’s heavy density.
Example problem 1
A lady of mass 80kg stands on a ground. if the contact are of her shoes is 180cm2., determine the pressure she exerts on the ground. (take g= 10Nkg-1).
solution
Force = weight of the lady = 80Kg x 10Nkg-1 = 800N
are is given as 180 cm2 and we need to convert it to SI unit.
therefore;
hence
pressure Problem 2
A ceramic block of mass 8kg is found to exert a pressure of 200Nm-2 on a surface. Determine it’s area that is contacting the surface. (take g = 10Nkg-1)
solution to the pressure problem
Force = 8kg x 10Nkg-1 = 800N
hence
Leave a Reply