Non-contact forces

Question 1 What are non-contact forces. Give few examples?

Question 2 When a plastic pen is rubbed in dry hair, it attracts tiny pieces of paper. Which force is involved in this process?

Question 3 A small piece pulls iron nails from a distance. Which force is involved in this process?

Question 4 An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. What force might be responsible for the attraction ?

Question 5 What is meant by magnetic force. Give example?

Question 6 What is meant by electrostatic force. Give example?

Question 7 What is meant by gravitational force. Give example?

Question 8 Why Our body hairs rises when we try to take off terylene or polyester shirt in the dry weather?

Question 9 Why the tiny pieces of paper move towards the comb and stick to it when rubbed with dry hairs?

Question 10 Why magnetic force is said to be a non-contact force?

A force Which can be exerted by an object on another object even from a distance is called non-contact force.

The examples of non contact forces:

1 Magnetic force

2 Electrostatic force

3 Gravitational force

Magnetic Force

A magnet attracts things made of iron or steel. Since the iron nails and pins move towards the magnet, it means that the magnet exerts a force on them. The force exerted by a magnet is called magnetic force. The magnet exerts a magnetic force on objects made of iron, Steel, Nickel ant Cobalt. It does not exert force on objects made of copper, wood or glass.

Since a magnet can exert magnetic force on Iron objects from a distance therefore magnetic force is a non contact force. The magnetic force between iron objects and a magnet is always attractive.

 

The magnetic force between two magnets placed near one another can be that of attraction or repulsion depending upon which poles of the two magnets are facing one another. A north Pole of magnet and another north pole are like pole. South Pole and another south pole are like poles. North pole and South Pole are unlike poles.

The like poles of two magnets repel each other where as unlike poles of magnet attract each other. There is a magnetic force of repulsion between the like poles of 2 magnet whereas there is a magnetic force of attraction  between between the unlike poles of magnet.

A magnet can exert a force on another magnet even from a distance without touching the other magnet, so the magnetic force exerted by one magnet on the other magnet is an example of non contact force.

(1) Many toys work due to the magnetic force exerted by magnets fixed inside them.

(2) The magnetic strips held to keep the refrigerator doors closed tightly.

(3) Certain stickers stick to the iron objects like Steel almirah, refrigerators etc. without any glue. Such stickers contain tiny magnets and hence stick to the iron object due to magnetic force.

(4) Magnetic force exerted by powerful electromagnet is used to separate scrap iron objects from among a heap of waste material.

Electrostatic Force

The force exerted by an electrically charged object is called electrostatic force. The electric charges are of two types: positive electric charge and negative electric charge .

Electric charges can be produced  by friction when one object is rubbed over another object. Electrostatic  means stationary electric charge. An object having stationary electric charge on it is called electrically charged object.

An electrically charged object can exert an electrostatic force on an uncharged objects.

For example: A plastic comb which is electrically charged by rubbing in dry hairs, exerts an electrostatic force on  uncharged tiny pieces of paper and attracts them. If we take a plastic comb and rub it in our dry hair for about 1 minutes and then bring it near the tiny pieces of paper. This comb attracts the pieces of paper. The tiny pieces of paper moves towards the comb and stick to it. When the plastic comb is rubbed in dry hairs, the comb gets electric charges by friction. This electrically charged comb is brought near the tiny pieces of paper it exerts an electrostatic force of attraction on them. Due to this electrostatic force the tiny pieces of paper move towards the comb and stick to it.

 

It is the electrostatic force which is responsible for raising our body hair when we try to take off a polyester or terylene shirt in dry weather.
If an inflated balloon is rubbed with a piece of synthetic cloth and then pressed against a wall, the balloon sticks to the wall. It is the electrostatic force which is responsible for the attraction between balloon and the wall. When the balloon is rubbed with a piece of synthetic cloth the balloon gets electrostatic charges and hence gets electrically charged. The electrically charged balloon attracts the uncharge wall and sticks to it.

The electrostatic force can be exerted by charged object on another object from a distance. So, electrostatic force is an example of non contact force. The electrostatic force between any charged object and an uncharged object is always attractive.

The electrostatic force between two charged objects having like charges is that of repulsion.

The electrostatic force between two charged objects having unlike charges is of attraction.

Gravitational Force

The pull exerted by objects possessing mass is called gravitational force the gravitational force between the objects is a force of attraction and it acts even if the two objects are not connected by any means.

It is the gravitational force between the sun and the earth which holds the earth in its orbit around the sun.

It is the gravitational force between earth and the moon which holds the moon in its orbit around the sun.

The gravitational force between two ordinary objects having small masses is very weak and cannot be detected easily. The gravitational force becomes strong only if one of the object has a huge mass.

If we drop a stone from some height it falls down towards the earth. This is because the earth exerts a gravitational force of attraction on the stone and pulls it down. The force with which the earth pulls the object towards it, is called the force of gravity.

When a child falls from a tree, it is the force of gravity which brings the child down to earth.

When a diver dives into a swimming pool, it is the force of gravity which brings him down.

The force of gravity causes all the objects to fall towards the earth.

A leaf falls from the tree due to gravity.

A fruit also falls down from a tree due to force of gravity.

Rain falls down to earth due  to the force of gravity.

When a coin slips from our hand, it falls to the ground due to the force of gravity acting on it .

When a pen slips from our hand it falls to the ground because of force of gravity acting on it. And a ball thrown upward also falls back to the earth due to the force of gravity. The gravitational force of earth acts on object from a distance therefore gravitational force of gravity is an example of non contact force.