**Position or Location**

**Position or Location**

The position of a particle is always w.r.t some reference point (origin) of given frame of reference. If the position of a particle w.r.t a given frame of reference is changing with time, the particle is said to be in motion w.r.t the given frame of reference. We represent the position of a particle at any instant by position vector as shown in the figure.

Position-time graph of a particle which is at A at time t_{1} and at B at time t_{2}.

represent the positions of the particles at t_{1} and t_{2}, respectively.

**Displacement**

The change in position vector of the particle for a given time interval is known as its displacement. From the figure, we can observe that the particle is moving from A to B via the path ACB in time interval

Displacement is a vector quantity and its SI unit is a metre.

**Distance**

The length of the actual path traversed by a particle is termed as distance traveled by a particle in given time interval. For shown situation the distance travelled by particle at the time interval t_{2} – t_{1} is the length of the path ACB. Distance is a scalar quantity and its SI unit is a metre.

**Comparison between distance and displacement**

♦For a moving particle in a given time interval distance there can be many valued functions, but displacement would always be to single valued function.

♦Displacement can decrease with time, but distance would be always +ve.

♦Displacement can decrease with time, but distance can never decrease with time.

♦Distance is always greater than or equal to the magnitude of displacement.

♦Distance is always equal to displacement, only if the particle is moving along a straight line without any change in direction.

**Average Speed and Average Velocity**

Average speed and average velocity are always defined for a time interval.

Average speed over a time interval is defined as the ratio of total distance travelled in given time interval to the time interval.

Comparisons between v_{av} and →v_{av }can be done in a similar way to what we have done for distance and displacement.