Force
Kinds of Forces
Force is a physical cause which changes (or tends to change) either the size or shape or the state of
rest or motion of the body.
The forces which act on bodies when they are in physical contact are called contact forces.
When a body moves over a rough surface, a force acts on the body in a direction opposite to the
motion of the body along the surface of contact. This is called the frictional force or the force of friction.
When a person moves towards the right on a road, the force of friction acts on him towards the left.
This force resists his motion on the road.
When a body is placed on a surface, the body exerts a force equal to its weight in the downward
direction on the surface. However, the body does not move (or fall) because the surface exerts an
equal and opposite force on it, which is called the normal reaction force.
When a body is suspended by a string, the body pulls the string vertically downwards due to its weight.
In its stretched condition, the string pulls the body upwards by a force which balances the weight of the
body. This force developed in the string is called the tension force T.
The spring has a tendency to return to its original form. Similarly, when one end of a spring is kept
fixed, the spring is found to exert a force at its other end which is directly proportional to the
displacement, and the force exerted is in a direction opposite to the direction of displacement. This
force is called the restoring force.
When two bodies collide, they push each other. As a result, equal and opposite forces act on each
body.
, The forces experienced by bodies even without being physically touched are called non-contact forces
or forces at a distance.
In the Universe, each particle attracts another particle because of its mass. This force of attraction
between the particles is called the gravitational force.
The force on a body due to the Earth’s attraction is called the force of gravity. It causes the movement
of the body towards the Earth, i.e. downwards, if the body is free to move. The body also attracts the
Earth by an equal amount of force, but no motion is caused in the Earth because of its huge mass.
Two like charges repel, while two unlike charges attract each other. The force between the charges is
called the electrostatic force.
Two like magnetic poles repel each other, while two unlike magnetic poles attract each other. The force
between the magnetic poles is called the magnetic force.
General Character of Non-contact Forces
1. The gravitational force is always of an attractive nature, while the electrostatic force and the
magnetic force can be either attractive or repulsive.
2. The magnitude of non-contact forces on the two bodies varies inversely as the square of the
distance of separation between them. It decreases with an increase in separation and increases as
the separation decreases.
Newton’s First Law of motion
Newton’s First Law: A body remains in the state of rest or of uniform motion in a straight line unless
an external force is applied on it.
The property of an object by virtue of which it neither changes its state nor tends to change its state is
called inertia. It is an inherent property of each object.
Kinds of Forces
Force is a physical cause which changes (or tends to change) either the size or shape or the state of
rest or motion of the body.
The forces which act on bodies when they are in physical contact are called contact forces.
When a body moves over a rough surface, a force acts on the body in a direction opposite to the
motion of the body along the surface of contact. This is called the frictional force or the force of friction.
When a person moves towards the right on a road, the force of friction acts on him towards the left.
This force resists his motion on the road.
When a body is placed on a surface, the body exerts a force equal to its weight in the downward
direction on the surface. However, the body does not move (or fall) because the surface exerts an
equal and opposite force on it, which is called the normal reaction force.
When a body is suspended by a string, the body pulls the string vertically downwards due to its weight.
In its stretched condition, the string pulls the body upwards by a force which balances the weight of the
body. This force developed in the string is called the tension force T.
The spring has a tendency to return to its original form. Similarly, when one end of a spring is kept
fixed, the spring is found to exert a force at its other end which is directly proportional to the
displacement, and the force exerted is in a direction opposite to the direction of displacement. This
force is called the restoring force.
When two bodies collide, they push each other. As a result, equal and opposite forces act on each
body.
, The forces experienced by bodies even without being physically touched are called non-contact forces
or forces at a distance.
In the Universe, each particle attracts another particle because of its mass. This force of attraction
between the particles is called the gravitational force.
The force on a body due to the Earth’s attraction is called the force of gravity. It causes the movement
of the body towards the Earth, i.e. downwards, if the body is free to move. The body also attracts the
Earth by an equal amount of force, but no motion is caused in the Earth because of its huge mass.
Two like charges repel, while two unlike charges attract each other. The force between the charges is
called the electrostatic force.
Two like magnetic poles repel each other, while two unlike magnetic poles attract each other. The force
between the magnetic poles is called the magnetic force.
General Character of Non-contact Forces
1. The gravitational force is always of an attractive nature, while the electrostatic force and the
magnetic force can be either attractive or repulsive.
2. The magnitude of non-contact forces on the two bodies varies inversely as the square of the
distance of separation between them. It decreases with an increase in separation and increases as
the separation decreases.
Newton’s First Law of motion
Newton’s First Law: A body remains in the state of rest or of uniform motion in a straight line unless
an external force is applied on it.
The property of an object by virtue of which it neither changes its state nor tends to change its state is
called inertia. It is an inherent property of each object.
