# Science: Motion and Its Description: Motion and Rest, Types of Motion (For CBSE, ICSE, IAS, NET, NRA 2022)

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## Motion and Rest

• Motion is a continuous change in the position of an object with respect to a stationary object.
• It is described in terms of displacement, distance, velocity, acceleration, time and speed.
• We can conclude that motion is a continuous change in the position of the object with respect to the observer.
• If a body stays at the same position with time, it is at rest. If the body changes its position with time, it is in motion.

## Types of Motion

### Rectilinear Motion

if the position of moving objects is changing with respect to time along a straight line. This type of motion is called motion in a straight line or rectilinear motion.

Ball rolling on horizontal surface.

### Circular Motion

If in a motion, an object follows circular path during motion. This type of motion is called circular motion.

### Oscillatory Motion

In such a motion, an object oscillates about a point often called position of rest or equilibrium position. The motion of swing and pendulum of wall clock are also oscillating motions.

## Distance

• Points of start and destination are connected by a path taken by the object during its motion. The length of the path followed by object is called distance.
• It is a scalar quantity.
• Its SI unit is meter (m) .

## Displacement

In any motion, you will notice that object gets displaced while it changes its position continuously. The change in position of the object is called displacement. it is the shortest distance between initial and final position of the object. It is a vector quantity.

## Uniform and Non- Uniform Motion

The motion in which an object covers equal distance in equal interval of time is called uniform motion whereas the motion in which distance covered by object is not equal in equal interval of time is called non-uniform motion.

 Time in seconds (t) 0 10 20 30 40 50 Position of A (x1 in meter) 0 4 8 12 16 20 Position of object B (x2 in meter) 0 4 12 12 12 20

The motion of object A is uniform and of object B is non-uniform.

## Speed

Speed can be defined as the distance travelled by a body in unit time.

Thus,

Its SI unit is meter per second which is written as ms – 1. The other commonly used unit is km h – 1.

i.e.. , 1 kmh – 1 = 1000 m = 5 ms – 1

## Velocity

The velocity is the ratio of length of the shortest path i.e.. displacement to the time taken. Velocity has same unit as the unit of speed i.e.. , ms – 1 (S. I. unit) or kmh – 1. The shortest path or the displacement is directed from initial position of the object to the final position of the object. Hence, the velocity is also directed from initial position of the object to the final position of the object.

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