Muscular force
Force which is exerted by muscles of the body is called Muscular force
All our body activities like lifting, walking, running, bending is because of muscular force
It is a contact force because muscular force can only be exerted on physical contact
Example 1
When we lift a book by our hand,it is because of muscular force of our hand
Our hand must be in contact with book,only then we are able to lift it
Example 2
When we walk,it is because of muscular force of our legs
Our legs must be in contact with the ground,only then we are able to walk
Example 3
To lift heavy weights, we use muscular force
Muscular Force by Animals
Animals like bulls and horses use their muscular force to move bullock carts and horse carts
Friction
The force which opposes motion of one body over another body is called friction
It is a contact force because it is exerted only when this force is exerted by one body on another body
Example 1
A ball which is moving comes to rest after some time
This is due to force of friction
This friction opposes motion of ball on the ground and brings it to rest.
Note-
Friction is a contact force because ball should be in contact with ground only then force of friction occurs and ball stops
Example 2
Boat comes to rest if we stop rowing
This is due to force of friction
This friction opposes motion of boat on the river and brings it to rest.
Friction is a contact force because boat should be in contact with the river only then force of friction occurs and boat stops
Example 3
A car comes to rest when engine is switched off
This is due to force of friction
This friction opposes motion of car on the road and brings it to rest.
Friction is a contact force because both car and river shall be in contact with each other,only then force of friction occurs and boat stops
