What is Speed in Physics? | Definition, Type, Formulas, Units – Motion in a Straight Line

Speed in Physics Formula:
The time rate of change of position of the object in any direction is called speed of the object.
Speed Formula in Physics

\(Speed (v)=\frac{\text { Distance travelled }(s)}{\text { Time taken }(t)}\)

  • Its SI unit is m/s.
  • It is a scalar quantity.
  • Its dimensional formula is [M°LT-1].

What is Speed in Physics? | Definition, Type, Formulas, Units – Motion in a Straight Line

We are giving a detailed and clear sheet on all Physics Notes that are very useful to understand the Basic Physics Concepts.

Types of Speed in Physics

Uniform Speed Definition:
If an object covers equal distances in equal intervals of time, then its speed is called uniform speed.

Non-uniform Definition or Variable Speed:
If an object covers unequal distances in equal intervals of time and vice-versa then its speed is called non-uniform or variable speed.

Average Speed Definition:
The ratio of the total distance travelled by the object to the total time taken is called average speed of the object.

\(Average speed =\frac{\text { Total distance travelled }}{\text { Total time taken }}\)

If a particle travels distances s1, s2, s3,… with speeds v1 v2, v3,……., then

\(\text { Average speed }=\frac{s_{1}+s_{2}+s_{3}+\ldots}{\left(\frac{s_{1}}{v_{1}}+\frac{s_{2}}{v_{2}}+\frac{s_{3}}{v_{3}}+\ldots\right)}\)

If particle travels equal distances (s1 = s2 = s) with velocities v1 and v2, then

\(\text { Average speed }=\frac{2 v_{1} v_{2}}{\left(v_{1}+v_{2}\right)}\)

If a particle travels with speeds v1, v2, v3,… during time intervals t1, t2, t3,…… then

\(\text { Average speed }=\frac{v_{1} t_{1}+v_{2} t_{2}+v_{3} t_{3}+\ldots}{t_{1}+t_{2}+t_{3}+\ldots}\)

If particle travels with speeds v1 and v2 for equal time intervals, i.e. t1 = t2 = t, then

\(Average speed =\frac{v_{1}+v_{2}}{2}\)

When a body travels equal distance with speeds v1 and v2, the average speed (v) is the harmonic mean of two speeds, i.e.


Instantaneous Speed Definition:
When an object is travelling with variable speed, then its speed at a given instant of time is called its instantaneous speed.

\(\text { Instantaneous speed }=\lim _{\Delta t \rightarrow 0} \frac{\Delta s}{\Delta t}=\frac{d s}{d t}\)

Motion in a Straight Line Topics:

Motion in Physics Rest and Motion
Frames of Reference Distance and Displacement
Measurement of Speed Velocity
Acceleration Uniform Motion and Non-Uniform Motion
Graphs of Motion Uniformly Accelerated Motion
Motion Under Gravity