Newton's laws of motion are very important in the classical physics. A large number of principles and results may be derived from Newton's laws. The first two laws relate to type of motion of a system that results from a given set of forces. These laws also help to define certain terms like mass , acceleration and force . Thus, these laws are kind of like definitions.

**Objectives**

- Define the first three laws with brief explanation
- Understand how the change of frame affects the application of these laws
- Create a systemic algorithm for making equations while problem solving
- Understand the concept of Pseudo forces
- Define Inertia

## First Law of Motion

If the vector sum of all the forces acting on a particle is zero then and only then the particle remains unaccelerated (i.e. either at rest or in uniform motion). |

This concept is meaningful, however, only when a frame of reference is specified. When we look at the acceleration of the particle of different frames we find it to be different.

^{2}. in the downward direction.

Consider the lamp in the cabin. THe forces acting on the lamp are the gravitational force *W* by the eath and the electromagnetic force *T* (tension) by the rope. Th direction of *W* is downward and the direction of *T* is upward. The sum is (*W*-*T*) downward.
Measure the acceleration of the lamp from the frame of reference of the cabin. The lamp is at rest. The acceleration of the lamp is zero. The person A measured this acceleration and uses Newton's first law to conclude that the sum of the forces acting on the particle is zero i.e.,

- $ W - T = 0 $ or, $ W = T $

Instead if we measure the acceleration from the ground, the lamp has an acceleration of 9.8 m/s^{2}. Thus, *W - T* ≠ 0 or W ≠ T.
Will surely complete this article soon. You can also help complete the topic for second law.