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

Types of 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

Motion in a Straight Line
  • 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.