Laws Of Motion

Front 1

When a force is applied on a body, what are the 2 main effects produced?

Back 1

1. It can change the state of rest or of motion of the body i.e., it can produce motion in the body.

2. It can change the size or shape of the body i.e., it can change the dimensions of the body.

Front 2

What is a force?

Back 2

A force is that physical cause which changes (or tends to change) either the size or the shape or the state of rest or of motion of a body.

Front 3

What are 2 kinds of forces?

Back 3

1. Contact forces

2. Non-contact forces

Front 4

What are contact forces, and when are they produced?

Back 4

The forces which are applied on bodies by making a physical contact with them, are called contact forces.

These forces are produced and experienced when a body comes in contact with another body.

Front 5

Examples of contact forces:

Back 5

1. Frictional force

2. Normal reaction force

3. Force of tension exerted by a string

4. Force exerted by a spring

5. Force exerted on 2 bodies during collision

Front 6

What is frictional force?

Back 6

When a body slides (or rolls) over a rough surface, a force starts acting on the body, in a direction opposite to the motion of the body, along the surface in contact.

This is called frictional force.

Front 7

What is normal reaction force?

Back 7

When a body is placed on a surface, the body exerts a force downwards, equal to its weight, on the surface, but the body does not move (or fall) because the surface exerts an equal and opposite force on the body normal to the surface.

This is called normal reaction force.

Front 8

What is tension force as applied through strings?

Back 8

When a body is suspended by a string attached to a rigid support, the body, due to its weight W, pulls the string vertically downwards and the string in its stretched condition pulls the body upwards by a force which balances the weight of the body.

This force developed in the string is called tension (or the force of tension) T.

Front 9

What is force exerted by a spring?

Back 9

Consider a spring with its one end kept fixed.

If it's other end is either stretched or compressed, the spring exerts a force F opposite to the direction of displacement of its free end, the magnitude of this force is directly proportional to the magnitude of displacement i.e., it's elongation or compression.

This force is called restoring force.

A spring balance works on this principle.

Front 10

What is force exerted by a spring on a horizontal spring?

Back 10

A horizontal spring with 2 objects, A and B attached at its 2 ends, in its normal form, or shape, does not exert any force on the object attached at it ends.

But, if the spring is compressed, it pushes away each object with a restoring force F at its ends.

While if the spring is stretched, it pulls in each object with a restoring force F at its ends.

In each case, the spring has a tendency to come back to its original form or shape.

Front 11

What is force exerted during collision?

Back 11

When 2 bodies collide, they push each other.

As a result, an equal and opposite force acts on each body.

These forces are the force of action and force of reaction.

Front 12

Example of force exerted during collision:

Back 12

A body B while in motion collides with a moving body A, and exerts a force F_ab on the body A, which is called the force of action. At the same instant, the body A also exerts an equal and opposite reaction force F_ba on the body B. As a result of these forces, the 2 bodies move apart after the collision.

Front 13

What are non-contact forces?

Back 13

The forces experienced by bodies even without being physically in touch, are called non-contact forces or forces at a distance.

Front 14

Examples of non-contact forces:

Back 14

1. Gravitational force

2. Electrostatic force

3. Magnetic force

Front 15

What is gravitational force?

Back 15

In the universe, each particle attracts the other particle due to its mass.

This force of attraction between them is called gravitational force.

Front 16

What is "the force of gravity" or the "weight of the body"? Explain.

Back 16

The Earth also, because of its mass, attracts all other masses around it.

The force on a body due to Earth's attraction is called the force of gravity or the weight of the body.

It causes motion in the body towards the Earth (downwards) if the body is free to move.

Thus, it is the force of gravity that makes a body fall, when released from a height.

The body also attracts the Earth by an equal force, but no motion is caused in the Earth because of its huge mass.

Front 17

What is electrostatic force?

Back 17

2 like charges repel, while 2 unlike charges attract each other.

The force between the charges is called electrostatic force.

This force acts between the charged objects even when they are separated.

Front 18

What is magnetic force?

Back 18

2 like magnetic poles repel, while 2 unlike magnetic poles attract each other.

The force between the magnetic poles is called the magnetic force.

This force acts even when the magnetic poles are at a separation.

Front 19

What is the general character of non-contact forces?

Back 19

1. The gravitational force is always of attractive nature, while the electrostatic force and magnetic force can be either attractive or repulsive.

2. The magnitude of non-contact forces between 2 bodies depends on the distance of separation between them.

It decreases with the increase in separation and increases as the separation decreases.

It's magnitude varies inversely as the square of distance of separation i.e., on doubling the separation, the force becomes one-fourth.