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Force and law of motion | Part 1 | CBSE | Class 9

As we now force and law of motion class 9 for CBS curriculum is very important  and very vast chapter. In my previous post i discussed Motion. If you miss that you can also see that post. So we will complete it part by part. In this post we try to find answer of some questions.

  1. What is Force ?
  2. What is unit of force ?
  3. Effects of force ?
  4. Classification of force ?
  5. Balanced and unbalanced forces with example ?

What is Force ?

 Force is the ‘push’ or ‘pull’ which can make a body move, stop a moving body, change the direction and speed of a moving body. Force cannot be seen but the effect of force on an object can be seen or felt.

Force and law of motion

What is unit of force ?

The SI unit of force is Newton. It is abbreviate with symbol N. The CGS unit of force is Dyne. And the relation between Dyne with Newton is 1 Newton = 105 Dyne

Effects of Force

A force produces the following effects :-

  • It can move or tend to move an object.
  • Force can stop or tend to stop an object in motion.
  • It can change or tend to change the direction of motion of an object.
  • Force can increase or decrease the speed of an object.
  • It can change the shape or size of an object.
Force can move or tend to move an object.

When a force applied on a stationary body, it can either move the body or tend to move it. The motion of the body takes place in the direction of the applied force. Some examples of this are :

  • When a football is kicked it is set into motion.
  • A railway locomotive applies force on the railway wagons to set them into motion.
  • Horse applies force on the cart to pull it.
  • At times when you push a wall, you are unable to move it. The force applied by use tends to move the wall.
Force can stop or tend to stop an object in motion.

When a force applied on a moving body, it can either stop the body or tend to stop it. For this a force is applied opposite to the direction of motion of the body. Some examples of this are :

  • When a football in motion has to be stopped a force is applied opposite to the direction of motion of the football.
  • A railway locomotive applies brakes on the railway wagons to stop them.
  • If a rolling body comes to rest due to frictional force. This force acts opposite to the direction of motion of the body.
  • At times when you push a car in motion, you are unable to stop it. The force applied by use tends to stop the moving car.
Force can change or tend to change the direction of motion of an object.
  • When a football in motion kicked perpendicular to its motion its directions of motion changes.
  • A perpendicular force is required to make a particle move in a circular path. This force is called centripetal force. This force continuously changes the direction of motion of the body.
  • Cricketer applies a tangential force to change the direction of the cricket ball.
Force can increase or decrease the speed of an object.Force and law of motion

When a force is applied on a moving body, in the direction of motion or opposite to it, it can change the speed of the object. Some examples of this are :

  • When a football in motion and kicked in the direction of its motion its speed increases.
  • The speed of a car can decreased by applying brakes.
  • Speed of a cycle can increased by applying force on the pedals.
  • A freely falling object is accelerate towards the earth due to the gravitational attraction of the earth.
Force can change the shape or size of an object. When a force is applied on a moving body, in the direction of motion or opposite to it, it can change the speed of the object. Some examples of this are : (i) When a football in motion is kicked in the direction of its motion its speed increases.

When a force is applied on a body, it can change the shape or size of the object.

Some examples of this are :
(i) Blacksmith hammer a iron piece to give a shape of that.

Classification of force ?

In your syllabus Force and law of motion, Forces are classified as being of two types. (i) Contact force, (ii) Non-contact force

Contact Force :

The force which act on a body either directly or through some connector are called contact forces.
Examples : Biological force, muscular force, mechanical force and frictional force are the examples of contact
force.

Non-Contact Force :

The force which do not make a direct contact with a body and act through space, without any connector are called non-contact force.
Examples:

  • The force of gravity of the earth is a non-contact force which attracts all bodies towards the earth.
  • The electrostatics force can pull tiny bits of dry paper is a non-contact force.
  • A magnet can attract common pins of steel from a distance and hence the magnetic force is non-contact force.

Balanced Force :

When two forces of equal magnitude but acting in opposite directions on an object simultaneously then the object continues in its state of rest of uniform motion in a straight line. Such forces acting on the object are known as balance force.

Examples of balanced force :-

1. If we push a wall, the wall does not move at all i.e., it remains at rest. In this case, the force of push on the wall acts in the forward direction. On the other hand, the wall also exerts equal force on our hand in the backward direction. These two equal and opposite forces cancel out the effect of each other and hence these two forces are the balanced forces.

2. When we try to push a heavy box on a rough surface, it does not move.

3. In a tug of war, two terms pull a rope in opposite directions. If the rope does not move in any direction inspite of the fact that both the teams are applying forces in opposite directions, then the forces applied by both the teams are known as balanced forces.

Unbalanced Force :

When two forces of unequal magnitudes act in opposite directions on an object simultaneously then the object move in the direction of a large force. These forces acting on the object known as unbalanced forces.
Examples of unbalanced force :-
1. When a boy drags a box on the floor, then an unbalanced force is acting on the box.
2. A bicycle will slow down if the rider stop pedaling it.

Here you can see full video tutorial of Force and law of motion

Let’s check how you learn Force and law of motion ?

Graphical Representation of Motion for class 9 cbse

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Subham

Subham

Hi myself Subham Dutta, having 15+ years experience in filed of teaching. I love to teach and try to build foundation of students. Try to make them imagine what they learn.

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