# Motion in a Straight Line: Types of Rectilinear/Linear Motion, Uniform Motion in a Straight Line (For CBSE, ICSE, IAS, NET, NRA 2022)

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• A body is said to be in motion if it changes its position with respect to time.
• Motion is one of the significant topics in physics. Everything in the universe moves.
• It might only be a small amount of movement and very-very slow, but movement does happen.
• Even if you appear to be standing still, the Earth is moving around the sun, and the sun is moving around our galaxy.
• There are two branches in physics that examine the motion of an object.
• Kinematics: It describes the motion of objects, without looking at the cause of the motion.
• Dynamics: It relates the motion of objects to the forces which cause them.

## Types of Rectilinear/Linear Motion

• The Rectilinear Motion or linear motion can be of two types:
• Non-Uniform linear motion with non-zero acceleration or variable velocity
• Uniform linear motion with zero acceleration or constant velocity
• Simplest type of one-dimensional motion is linear motion.
• As per Newton՚s first law of motion, an object will either be in rest or continue to move in a straight line with a uniform velocity unless and until an external force is applied to it.
• Linear motion is often mistaken for general motion. Linear motion is a one-dimensional motion but in general, the motion has both magnitude and direction, i.e.. , an object՚s position and velocity are described in vector quantities.

## Uniform Motion in a Straight Line

• A body is said to have uniform acceleration if the rate of change of its velocity remains constant.
• A body is said to be in a uniform motion if it travels in a straight line covering equal distances in equal intervals of time.

Example:

If a car travels at a speed of 60 km/hour then it will cover 1 km/minute. In this sense, the motion of car acceleration is uniform.

## Non-Uniform Motion in a Straight Line

• While in movement, the rate of change of its velocity changes at different points of time.
• A body is said to have a non-uniform motion when the velocity of a body changes by unequal amounts in equal intervals of time.

Example:

A boy kicking a football.

## Position, Displacement and Distance

• Position, displacement, and distance in this module, we are only talking about motion in a straight line.
• For convenience, we will measure distance in meters and time in seconds.
• For a horizontal line, there are only two directions to consider: right and left.
• For a vertical line, the two directions are up and down.
• We choose a point O on the line, which we call the reference point or origin.

### Displacement

Displacement is the change in position of a body. The magnitude of displacement between the same points is proportional to the path length.

### Uniform Motion

When the displacement of an object is equal in equal time intervals, the motion is said to be uniform, else it is referred to as non-uniform.

### Average Speed

It is referred to the ratio between the total path length traversed to the time taken.

### Instantaneous Velocity

When the limit of the average velocity has an indefinitely smaller interval of time.

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