# Class 8 Force And Pressure Notes

## Force :–

A push or pull on an object is called force.

• S.I Unit = Newton

### 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.