2.2 Average speed and velocity

  Motion in One Dimension

Speed is the rate at which the particle is moving.

In other words, the average speed is defined as the ratio of distance travelled to the total time taken.

Mathematically average speed can be written as,
$${v_{avg}} = \frac{{{\text{Total distance travelled}}}}{{{\text{Total time taken}}}}$$$${v_{avg}} = \frac{{\Delta s}}{{\Delta t}}$$

Note:

• Speed is a scalar quantity
• SI unit of speed is $m/s$
• Speed of a body cannot be zero or negative

Velocity: is defined as the rate of change of position.

In other words, average velocity is defined as the ratio of displacement to the time taken.

Mathematically average velocity is given by,
$${\overrightarrow v _{avg}} = \frac{{\Delta \overrightarrow r }}{{\Delta t}}$$
where ${\Delta \overrightarrow r }$ is the displacement of particle in time ${\Delta t}$.

Note:

• Velocity is a vector quantity
• SI unit of velocity is $m/s$
• Velocity can be positive, negative or zero
• The value of velocity can never be greater than the speed.