Class 8 Force And Pressure Notes

Force :–

A push or pull on an object is called force.

S.I Unit = Newton

Effects of Force :-

Change in state of motion :-

Change in the speed of an object.
Change in its direction of motion.

Change in shape and size of an object :-

We can change shape and size of an object by compressing, stretching and bending the object.

Types of Force :-

Contact Force :-

The type of force that came into action when two bodies or object are in physically contact with each other.

(1) Muscular Force :-

The force resulting due to the action of muscles is known as the muscular force.
Ex :- Lifting a heavy box, pulling a bucket of water, pedalling a cycle.

(2) Friction :-

The force that opposes the relative motion between two surfaces is known as Frictional force.

Acts between the surface of the two bodies in contact.

Non-Contact Force :-

The type of force that do not need contact for action is known as Non-contact force.

(1) Magnetic Force :-

A magnet exert force on another magnet or magnetic material without being in contact with it. the force, exerted in this case, is known as magnetic force.
Ex :- Force between Magnet and iron.

(2) Gravitational Force :-

The attractive force that pulls objects towards the center of earth is called gravitation force.

Property of the universe, every object attracts or exerts a force on every other object.

(3) Electrostatic Force :-

The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.

Pressure :-

The force acting on a unit area of a surface is called pressure.

Pressure = Force / Area
S.I Unit = Pascal

Pressure Exerted by Liquids and Gases :-

It is the force exerted by liquids or gases per unit area.
Liquids and gases exert pressure in all directions. The pressure inside a them increase with depth.
Liquid pressure, on the bottom of the container (due to weight of liquid column), does not depend on the area of the bottom.
Liquid pressure at any point inside the liquid, depends upon the density of the liquid and the height of liquid column above the point.

Atmospheric Pressure :-

The air present in atmosphere exerts a pressure on the earth which is called atmospheric pressure.

The value of atmospheric pressure at the sea level is 101325 Pascal.
The atmospheric pressure keeps on increasing as we move towards the Earth’s surface.
Atmospheric pressure exists in all directions. The instrument used for the measurement of atmospheric pressure is known as a barometer.

Class 8

Class 8 Force And Pressure Notes