FORCE AND LAWS OF MOTION / THE LAWS OF MOTION – SUMMARY

Summary –

• If the resultant of all the forces acting on a body is zero, the forces are called balanced forces.
• If the resultant of all the forces acting on a body is not zero, the forces are called unbalanced forces. An unbalanced force acting on a body gives it an acceleration.
• Force is an external effort in the form of pushing, pulling, stretching, compressing, etc.
• First law of motion – An object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force.
• The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia.
• The mass of an object is a measure of its inertia. Its SI unit is kilogram (kg).
• There are three types of inertia –
  (i) inertia at rest,
  (ii) inertia of motion,
  (iii) inertia of direction.
• All inertia examples are examples of Newton’s first law of motion.
• Force of friction always opposes motion of objects.
• Second law of motion – The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force.
• Force is a physical quantity that changes or tends to change the state of rest or of uniform motion of a body in a straight line. It is a vector quantity that has magnitude and direction. The SI unit of force is kg m s-². This is also known as newton (N). A force of 1newton produces an acceleration of 1 m s-² on an object of 1 kg mass.
• The momentum of an object is the product of its mass and velocity and has the same direction as that of the velocity. Its SI unit is kg m s-1.
• Newton’s first and second laws deal with force and its effects on motion of objects.
• Third law of motion – To every action, there is an equal and opposite reaction and they act on two different bodies. Hence, they do not cancel each other.
• Newton’s third law deals with relationship between forces on two interacting bodies. Force never occurs singly in nature.
• The motion of a rocket is based on Newton’s third law of motion.                     
• In an isolated system ( where there is no external force), the total momentum remains conserved. In a collision momentum is conserved.

---

Latest CBSE syllabus topics –
Force and Newton’s Laws – Force and Motion, Newton’s laws of motion, Inertia of a body, Inertia
and mass, Momentum, Force and acceleration, Elementary idea of conservation of momentum,
action and reaction forces.

Latest Maharashtra SSC Board syllabus topics –
The Laws of Motion – Force and Motion, Newton’s first law of motion, Newton’s second law of motion, Newton’s third law of motion, Inertia of a body, Inertia and mass, Momentum, Force and acceleration,
Elementary idea of conservation of momentum, action and reaction forces.

---

INTRODUCTION 

We have seen effects of forces in our daily life like lift, pulling passengers up; train pulling carriages etc. A push or pull on a body is called force. Some examples are pulling the drawer of the table, stretching a rubber band, twisting a wet cloth to squeeze out water, pushing of leaves by wind etc.

Effects of force

A force is not visible but it can be judged by the effects which it can produce in various bodies. The effects of force are –

• A force can move a stationary body.
• A force can stop a moving body.
• A force can change the speed and velocity of a moving body.
• As it can change the velocity, therefore, the force can change the direction of a moving body.
• A force can change the shape and size of a body.

Force can change the shape and size of a body. For example, when we take a spring and pull it at both ends with our hands, then the shape and size of the spring changes.The shape of dough (kneaded flour) changes on pressing it with a roller to make bread.The shape of kneaded wet clay changes when a potter converts it into pots of different shapes. This happens because the potter applies force on the kneaded wet clay. When a balloon is pressed, it changes its shape due to effect of force.
Force has magnitude and direction, therefore it is a vector quantity. Force changes the state of an object from rest to motion in a straight line or from motion to rest .

---

Next – 

Balanced and Unbalanced Force, Inertia