CBSE Class -8th || Force and Types of Forces || By Pratap Sanjay Sir

Force and Motion

Definition of Force

Force is a push or pull acting upon an object as a result of its interaction with another object. It is a vector quantity, which means it has both magnitude and direction.

Types of Forces

Contact Forces:

• These are forces that result from physical contact between two objects.
• Examples: Muscular Force, frictional force, tension force, normal force.

Non-contact Forces:

• These are forces that act even when objects are not in physical contact.
• Examples: gravitational force, electromagnetic force, and nuclear force.

Effects of Forces

• Change in Speed: Forces can change the speed of an object.
• Change in Direction: Forces can change the direction of motion of an object.
• Change in Shape: Forces can change the shape of an object.
• Change in State of Rest: Forces can move an object from rest to motion or vice versa.

Newton's Laws of Motion

Newton's First Law (Law of Inertia):

An object will remain at rest or in uniform motion unless acted upon by an external force.

Example: A ball will stay still on the ground until someone kicks it.

Newton's Second Law (Law of Acceleration):

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

F = ma, where F is the force, m is the mass, and a is the acceleration.

Newton's Third Law (Action and Reaction):

For every action, there is an equal and opposite reaction.

Example: When you push against a wall, the wall pushes back with an equal force.

Contact Force

Muscular Force:

Muscular force is the force exerted by the muscles of the body.

Examples: Lifting a weight, kicking a ball, and pushing a door.

Frictional Force:

Friction is the force that opposes motion between two surfaces in contact.

• Types of frictional Force: static friction, kinetic friction, rolling friction.
• Applications: Car brakes, walking, gripping objects.

Non-Contact Force

Gravity or gravitational force:

Gravity is the force of attraction between objects with mass.

• It causes objects to fall towards the Earth's surface.
• Applications: Weight, planetary motion, tides.

Magnetic Force:

The force exerted between magnetic objects.

• Applications: Magnetic levitation, electric motors, compass.

Electrostatics Force:

The Force exerted by a charged body to another charged or unchanged body is know as electrostatic force.

• When we rub a comb or scale on dry hair, it gets charged and attract tiny pieces of paper.

Force and Motion Science Presentation Colorful Pictures by Pratap Sanjay Kumar (Sanjay Bhaiya ji)