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# CBSE Class 8 Physics Notes for Chapter 1 Force and Pressure

CHAPTER 1 FORCE AND PRESSURE

FORCE
A push or pull action is called force.
For a force to come into play, at least two objects must be in interaction.
If forces are applied on an object in the same direction, they get added.
If the two forces applied on the object act in opposite directions, the net force on the object is the difference between the two forces.
A force can change:

• the state of motion of an object.
• the shape of an object

CONTACT FORCES
The forces that require actual contact with an object to act on it are called contact forces.
Muscular force
The force that is exerted due to the action of the muscles is known as muscular force. A muscular force can be applied only when there is a contact between the force and an object.
Friction
Friction is a type of contact force. It acts in the direction opposite to the direction of motion of a body. Friction is the force responsible for the change in the state of motion of an object. Friction reduces the speed of a moving object

NON-CONTACT FORCES
The forces that do not require any actual contact with the object to act on it are called non-contact forces.

Magnetic force
A magnet can exert magnetic force on an object without being in contact with it. Hence it is a non-contact force.
Electrostatic force
The force that a charged body exerts on another body is called electrostatic force which is a non-contact force.
Gravitational force
The force with which the earth pulls objects towards itself is called gravitational force. This force is also a non-contact force.

PRESSURE
Force acting on a unit surface area is called pressure. Therefore,
Pressure=  Force/Area

It is not just solids which exert pressure. Both liquids and gases exert pressure on the walls of their container.

Atmospheric pressure: The pressure exerted by the atmosphere (i.e. the air around us) is called atmospheric pressure. It is basically the weight of air in a column of unit area. The atmospheric pressure is very high but the pressure of blood in our body counters it.