NCERT 9TH CLASS SCIENCE CHAPTER THRUST AND PRESSURE
THRUST AND PRESSURE
Thrust : Force acting normally on a surface is called the thrust.
Thrust is a vector quantity and is measured in the unit of force, i.e., newton (N).
Pressure : The thrust acting on unit area of the surface is called the pressure.
If a thrust F acts on a area A, then pressure (P) =
Pressure is directly proportional to the force.
Pressure in inversely proportional to the area.
For the examples :
Ex. A sharp knife cuts easily than a blunt knife by applying the same force.
Ex. A sharp needle pressed against our skin pierces it. But a blunt object with a wider contact area does not affect the skin when pressed against it with the same force.
1. The foundation of a building or a dam has a large surface area so that the pressure exerted by it on the ground is less.
This is done to prevent the sinking of the building or the dam into the ground.
2. The tyres of a bus or a truck have larger width than those of a car. Further, the number of tyres of heavy vehicles is more than four.
This is done to enable the tyres to carry more weight and to
prevent sinking into ground.
3. A sleeping mattress is so designed that when you lie on it, a large area of your body comes in its contact. This reduces the pressure on the body and sleeping becomes comfortable.