Concepts

Class 8
Chapter 11 Class 8 - Force And Pressure

## Magnetic Force

Force which is exerted by Magnets is called Magnetic Force

Magnets exert force on either other magnets or on iron

Both these are magnetic force

### Is Magnetic Force Contact Force or Non Contact Force?

It is a non contact force

Explanation

When one magnet is brought close to other magnet,both magnets move towards each other

Similarly if iron is brought near magnet,it moves towards

This happens without touching of both magnets

Hence, it is a non-contact force

## Electrostatic Force

Force which is exerted on a electrically charged body on  another body is called Electrostatic Force

Note

One body must be charged

The other body may be charged or uncharged

It is a non contact force because it works from Distance(even if 2 objects are not in physical contact with each other)

Example 1 - One Body Charged Other Uncharged

If one straw is rubbed with paper, it becomes electrically charged

If is brought near another straw which is not charged,they attract each other

Thus, charged body attracts uncharged body

Note

Electrostatic force is a Non Contact force as it works from distance(even if both objects are not in contact with each others)

Example 2 - Both Bodies are Charged

If 2 straws are charged and both near each other

They repel

Thus, 2 charged objects repel each other

Note-This happens without both straw touching each other,so it is a non contact source.

## Gravitational Force

Every object on earth which has a mass exert a force on another object

This force is called gravitational force

Note

Gravitational force is a Non Contact force as it works from distance (even if both objects are not in contact with each others)

Example 1

If we throw a ball up,it falls down automatically

This is because of gravity(gravitational force of earth on ball)

Ball keeps moving towards the earth even if both are not in contact with each other yet,so it is  Non Contact Force

Example 2

If we open a tap of water in a sink,water flows down

This is because of gravity(gravitational force of earth on water)

Water flows towards earth even though water and sink are not yet in contact with each other

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