Motion Physics | Courage Library

1. Introduction to Motion

Motion is the change in the position of an object with time.

Simple Definition:

An object is said to be in motion if it changes its position over time.

2. Types of Motion

Linear Motion

Motion in a straight line.

Example: A train moving on a straight track.

Circular Motion

Motion in a circular path.

Example: Movement of a fan blade.

Rotational Motion

The object rotates on its own axis.

Example: Earth rotating on its axis.

Periodic Motion

Motion that repeats at regular intervals.

Example: Pendulum of a clock.

Oscillatory Motion

Back and forth motion around a central point.

Example: Swing, tuning fork vibration.

3. Speed, Velocity, and Acceleration

Speed

Distance travelled per unit time.

Formula:

Speed = Distance / Time

SI Unit:

metre per second (m/s)

Velocity

Speed in a specific direction.

Type:

Vector quantity

SI Unit:

metre per second (m/s)

Acceleration

Rate of change of velocity.

Formula:

Acceleration = Change in velocity / Time

SI Unit:

metre per second square (m/s²)

Uniform Motion

Velocity remains constant.

Non-uniform Motion

Velocity changes with time.

4. Distance and Displacement

Distance

Total path covered (scalar quantity).

Displacement

Shortest path between initial and final position (vector quantity).

5. Newton's Laws of Motion

Sir Isaac Newton formulated three laws describing motion and force.

First Law

A body continues to be in its state of rest or uniform motion unless acted upon by an external force.

Known as:

Law of Inertia

Second Law

Force = Mass × Acceleration

Formula:

F = m × a

SI Unit of Force:

Newton (N)

Third Law

For every action, there is an equal and opposite reaction.

6. Inertia

Inertia is the property of a body to resist change in its state of motion.

Inertia of Rest

Tendency to remain at rest

Inertia of Motion

Tendency to remain in motion

Inertia of Direction

Tendency to maintain direction

7. Force

A force is a push or pull acting on an object.

SI Unit:

Newton (N)

Types of Forces:

Contact forces: friction, muscular force
Non-contact forces: gravitational, magnetic, electrostatic

8. Friction

Friction is a force that opposes motion.

Types of Friction:

Static friction
Sliding friction

Rolling friction
Fluid friction

Advantages:

Helps walking, writing, braking

Disadvantages:

Produces heat
Causes wear and tear

9. Gravity

Gravity is the force that attracts objects towards the Earth.

Value of g (acceleration due to gravity):

9.8 m/s²

Factors affecting gravity:

Maximum at poles
Minimum at equator

10. Mass and Weight

Mass

Amount of matter in a body.

SI Unit:

kilogram (kg)

Mass is constant everywhere.

Weight

Force with which Earth pulls an object.

Formula:

W = m × g

SI Unit:

Newton (N)

Weight changes with gravity.

11. Work

When a force moves an object in the direction of force, work is done.

Formula:

Work = Force × Displacement

SI Unit:

Joule (J)

If displacement is zero, work done is zero.

12. Energy

Energy is the ability to do work.

SI Unit:

Joule (J)

Main Forms of Energy:

Kinetic Energy

Energy due to motion

Formula:

KE = 1/2 × m × v²

Potential Energy

Energy due to position or height

Formula:

PE = m × g × h

Mechanical Energy

Sum of kinetic and potential energy.

Heat Energy

Due to temperature.

Chemical Energy

Stored in fuels and batteries.

Electrical Energy

Produced by electric current.

Nuclear Energy

Released during nuclear reactions.

13. Power

Power is the rate of doing work.

Formula:

Power = Work / Time

SI Unit:

Watt (W)

Conversions:

1 kilowatt (kW) = 1000 Watts
1 horsepower (hp) = 746 Watts

14. Law of Conservation of Energy

Energy can neither be created nor destroyed. It only changes from one form to another.

Example:

When a ball falls, potential energy converts into kinetic energy.

15. Simple Machines

Simple machines make work easier.

Examples:

Lever
Pulley
Wheel and axle

Inclined plane
Screw
Wedge

Mechanical Advantage

Efficiency of a machine in multiplying force.

16. Important SSC GD Points (Frequently Asked)

Newton's first law is law of inertia
Force unit = Newton
Energy unit = Joule
Power unit = Watt
Acceleration = m/s²

Weight = mass × gravity
g = 9.8 m/s²
Kinetic energy depends on velocity
Potential energy depends on height
Friction opposes motion
Work done = zero if displacement is zero

17. Quick Revision Table

Concept	Key Point	SI Unit
Speed	Distance per time	m/s
Velocity	Speed with direction	m/s
Acceleration	Rate of change of velocity	m/s²
Force	Push or pull	Newton
Work	Force × displacement	Joule
Energy	Ability to do work	Joule
Power	Work/time	Watt
Gravity	9.8 m/s²	m/s²

18. Memory Tricks for SSC GD

Force formula:

F = m × a

Energy formulas:

KE = 1/2 m v²
PE = m g h

Units:

Work → Joule
Power → Watt
Force → Newton

Newton's three laws:

Inertia
F = ma
Action = Reaction