Laws of Motion
A complete physics learning website covering Newton’s Laws of Motion, force, inertia, momentum, friction, circular motion, formulas, flowcharts, diagrams, solved examples, and practice exercises for students.
1. Introduction to Laws of Motion
The laws of motion were proposed by Sir Isaac Newton. These laws explain the relationship between force and motion.
Main Topics
- Force
- Inertia
- Momentum
- Action and Reaction
- Friction
2. Newton’s First Law of Motion
This law is also called the Law of Inertia.
Inertia
Inertia is the property of a body to resist any change in its state.
Example
Passengers move backward when a bus starts suddenly because their body tries to remain in the state of rest.
3. Newton’s Second Law of Motion
The rate of change of momentum is directly proportional to the applied force.
Meaning of Formula
| Symbol | Meaning |
|---|---|
| F | Force |
| m | Mass |
| a | Acceleration |
Solved Problem
A force produces an acceleration of 5 m/s² in a body of mass 10 kg. Find the force.
Given:
m = 10 kg
a = 5 m/s²
F = 10 × 5
F = 50 N
4. Newton’s Third Law of Motion
Examples
- Rocket launch
- Walking on ground
- Swimming
- Gun recoil
5. Momentum
Momentum is the quantity of motion possessed by a body.
Example
A body of mass 5 kg moves with velocity 4 m/s. Find momentum.
p = 5 × 4
p = 20 kg m/s
6. Friction
Friction is the force that opposes relative motion between surfaces.
Types of Friction
- Static friction
- Sliding friction
- Rolling friction
- Fluid friction
7. Circular Motion
Motion of an object along a circular path is called circular motion.
8. Practice Exercises
Short Questions
- State Newton’s first law.
- Define inertia.
- Write formula of force.
- State Newton’s third law.
- Define momentum.
Numerical Problems
- Find force acting on a 20 kg body accelerating at 3 m/s².
- Calculate momentum of a 4 kg body moving at 6 m/s.
- A force of 80 N acts on a body of mass 10 kg. Find acceleration.
- Find centripetal force for m = 2 kg, v = 5 m/s, r = 2 m.
9. Formula Summary
| Topic | Formula |
|---|---|
| Force | F = ma |
| Momentum | p = mv |
| Centripetal Force | F = mv²/r |
| Acceleration | a = (v-u)/t |