Contact force

Question 1 What are contact forces?

Question 2 Name 2 types of contact forces?

Question 3 Name the force which always opposes motion?

Question 4 Which force makes a rolling ball stop of its own?

Question 5 What is muscular force. Give example?

Question 6 What is frictional force. Give example?

Question 7 Name the type of force involved when a moving boat coming to rest when rowing is stopped?

Question 8 Why frictional force is said to be contact force?

Contact Force

A force which can be exerted by an object on another object only through physical touching is called a contact force.

The example of contact forces are:

(1) Muscular force

(2) Frictional force

Muscular Force

Suppose a book is lying on a table. To lift this book from the table, some force is required .When we lift this book from the table by hand, the force is exerted by muscles of our arms.

When we Kick a football, the force is exerted by the muscles of our legs. The force exerted by the muscles of the body is called muscular force .The human beings exert muscular force for performing the various activities like walking,  jumping,  running, climbing, lifting pushing, pulling, stretching, squeezing, twisting and pressing the objects.

It is the muscular force which enables us to perform all the activities involving the movement Or bending of our body parts. The muscular force also acts inside our body to perform various functions required our survival.

In the process of digestion it is the muscular force which pushes the food through the alimentary canal.

The expansion and contraction of lungs when we inhale and exhale during breathing also involves muscular force.

The beating of heart also takes place by the muscular force produced by cardiac muscles.

The animals like ox, camel and horse provide the force their muscles and help the man in doing jobs.

Ox pulls the plough by using its muscular force.

A horse and camel exerts their force in pulling the carts.

An elephant pulls heavy logs of wood by using muscular force.

Since the muscular force can be applied to an object only when our body is in contact with the object therefore muscular force is contact force. When we lift a book from a table by applying muscular force, then our hands is in contact with the book. When we hit a hockey ball we apply muscular force to ball through the hockey stick.

Frictional force

A ball moving on the ground slows down gradually and stops after covering some distance. The force is exerted by the ground on the moving ball which opposes its motion and brings it to a stop.

The force which always opposes the motion of one body over another body frictional force. It acts between the two surfaces which are in contact with each other.

A  ball moving on the ground slows down and stops due to frictional force between the ball and the ground.

The bicycle moving on the road slows down and finally comes to stop due to frictional force between the tyres of the bicycle and the road. This fictional force opposes the motion of bicycle and brings it to a stop. The two surfaces in contact are the surface of the road and the surface of tyres of bicycle.

The boat moving in water slows down and finally stops due to frictional force between the boat and water. The frictional force exerted by water opposes the motion of boat and makes it stop. The two surfaces in contact are the surface of boat and surface of water.

The fictional force always act on all the moving objects and its direction is always opposite to the direction of motion.

Since frictional force arises when the surface of two objects are in touch with each other, therefore, frictional force is an example of contact force.