Position – If we want to tell about the position of an object. We require :-

• Distance of the particle from the reference point
• Direction of the particle with respect to reference point.

Hence position is a vector quantity. Generally, origin is taken as reference point and axes are known as frame of references.

Rest- If a particle does not change it’s position with respect to some reference point, then it is said to be in rest.

Motion-If the position of a body is changing with respect to a frame of reference, the body is said to be in motion.

Rest are Motion are relative terms. It depends on the frame of reference.

Types of motion:-

1. Motion in ONE-DIMENSION- When a particle moves in a straight line, then it’s motion is said to be one dimensional motion. – OR – If only one co-ordinate of the position of a particle changes, then it’s motion is one dimensional.  Example – Motion or a freely falling body under ideal conditions.
2. Motion in TWO DIMENSION-When a particle moves in a pllane on curved path or zig-zag path, then it’s motion is said to be two dimensional motion. -OR- When two co-ordinates of the position of the body change with time, then it’s motion is two dimensional. Example- Motion of a motor car & all kind of Projectile Motions.
3. Motion in THREE DIMENSION- Whenever a particle moves in space randomly then it’s motion is said to be three dimensional motion. If all the three co-ordinates of position of a particle change with time, then it’s motion is three dimensional.  Example- Motion of a flying insect, Motion of a kite on a windy day.

Distance and Displacement

Distance : Length of actual path traveled by a body/ particle. It is a scalar quantity. And the SI unit is Metre.

Displacement: It is the shortest distance between initial and final position of a particle. It is always measured from initial to final position. It is a vector quantity and in SI system, it’s unit is also Metre.

Comparison between Distance & Displacement

1. Distance covered by a particle is always greater than or equal to displacement. Distance is equal to displacement only when particle is moving in a straight line in one direction.
2. For a moving particle, distance always increases with time while displacement may increase or decrease or it may be zero or negative.
3. For two fixed points, displacement is a single valued function while distance has many values.

Average Speed = (Distance Covered)/ (Time)

Speed- Distance covered by particle in unit time is called speed. It is a scalar quantity and in SI unit, it’s unit is metre/second.

Velocity- Velocity is the displacement covered by particle in unit time. It is a vector quantity and hence can be positive or negative.

Acceleration- The change in velocity per unit time. The rate of change of velocity with respect to time is called acceleration. It is a vector quantity and it’s direction is in the direction of change in velocity. It’s unit is metre/ second^2.

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