A body is said to be in motion when its position changes continuously with respect to a stationary body taken as a reference point.

Distance and Displacement Examples

The distance covered by a body is the actual length of the path traveled by the body between the initial position and final position.
The displacement of a particle is the change in position of the particle in a particle in a particular direction and is given by a vector drawn from its initial position to its final position.
In fig,(a), AB is the displacement and (AC+CD+DE+EB) is the distance traveled.
Also in Fig.(b), AC is displacement and distance covered is (AB+BC).


It is the distance moved by a moving body in unit time. Its unit is m/s or km/h.

Speed =Distance travelled/Time Taken or S=D/t or D=St

where,S=speed, D=distance, t=time taken
An object is said to be moving with a uniform speed, if it covers equal distances in equal intervals of time.
an object is said to be moving with a variable speed, if it covers equal distances in unequal intervals of time or unequal distances in equal intervals of time.
Average speed for a motion is the ration of the total distance travelled by the object to the total time taken.

Average speed Sav=D1+D2+…../t1+t2…..

If the body covers equal distance with different speeds then



It is the rate with which a body moves in a particular direction. It is a vector quantity.

Velocity=Displacement in particular direction/Time taken

A body is said to be moving with uniform velocity,if equal displacements of the body take place in same direction in equal intervals of time.
If a body moves in such away that its speed or the direction or both changes with time,the body is said to have variable velocity.

Average velocity of a body is defined as the net displacement divided by the time taken for displacement.

as net displacement =X2-X1 and time taken = t2-t1


The rate of change of position of a body with reference to moving observer is regarded as the relative velocity of body w.r.t. observer when the two are moving in same direction, then relative velocity =v1-v2 .When the two are moving in opposite directions, then relative velocity = v1+v2.


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