Physics - Motion

Introduction

Motion means change in position of an object in given period of time.
Motion, normally, is described in terms of displacement, velocity, acceleration, distance, time, and speed.

Motion along a straight line is the simplest form of motion.
Magnitude is the numerical value of a physical quantity.
The shortest distance, which is measured from the initial to the final position of an object is called as the ‘displacement.’
The magnitude of the displacement for a path of motion may be zero but the corresponding distance covered cannot be zero.
If an object travels equal distances in equal intervals of time, it is said to be in ‘uniform motion.’
If an object travels unequal distances in equal intervals of time, it is said to be in ‘non-uniform motion.’

The distance travelled by the object in unit time is known as the rate of motion or simply speed.
The SI unit of speed is meter per second (symbol m s^–1 or m/s).
The average speed of an object can be obtained by dividing the total distance travelled by the total time taken: represented as

$$Average\:Speed = \frac{Total\:Distance\:Travelled}{Total\:Time\:Taken}$$

If a quantity specifies the direction of motion along with its speed, it is known as velocity.
Velocity is the speed of a given object, which is moving in a defined direction.
Speed and velocity have the same measuring units, i.e., m s^–1 or m/s.

$$Average\:Velocity = \frac{Initial\:Velocity\:+\:Final\:Velocity}{2}$$

The change in the velocity of an object per unit time is defined as acceleration.
The acceleration is calculated as −

$$Acceleration = \frac{Change\:in\:Velocity}{Time\:Taken}$$

When an object moves in a circular path in uniform speed, its motion is known as uniform circular motion.

The motion of the earth and all other planets and their satellites is almost in a circular orbit at constant speed.