# Speed, Uniform speed, Variable speed, average speed, Instantaneous speed

Hello Friends, you must have heard about the term speed. For example, you are traveling in a car and there is an instrument known as a speedometer which shows the reading 60 but actually, it is 60 kilometers per hour or in short form 60 km/hr. We commonly say that car is traveling at a speed of 60 or my papa or mom is driving the car at speed of 60.

But there are other terms also like uniform speed, variable speed, average speed, and instantaneous speed also.

Let us discuss the definitions of speed, uniform speed, variable speed, average speed, and instantaneous speed and try to understand the difference between them in the following section:

**1. Speed:** The time rate of change of position of a body in any direction is known as its speed.

It is measured by the ratio of the distance by a body to the time in which this distance is covered

i.e. Speed = distance/time

Speed is a scalar quantity. It is either positive or zero but never negative.

Units of speed: We know that,

Speed = Distance/Time

Units of speed = Units of distance/Units of time

In the CGS system, a unit of speed is cms-1, and in the MKS system or SI units, the unit of speed is ms^{-1}.

**2. Uniform Speed:** A body is said to be moving with uniform speed if it covers equal distances in equal intervals of time, however small these intervals may be. For example, if a body starts at 5 pm and move till 6 pm and covers 60 KM. If body covers 10 Km in first 10 minutes then 10 KM in next 10 minutes and so on. It means body covers equal distances in equal intervals of time.

**3. Variable Speed:** A body is said to be moving with variable speed if it covers unequal distances in equal intervals of time, however small these intervals may be. In the above example, if the body covers 10 Km in the first 10 minutes then 12 Km in the next 10 and then 8 in the next 10, and so on. It means the body is covering unequal distances in equal intervals of time.

**4. Average Speed:** Average speed of a body is defined as that uniform speed with which it covers the same distance in a given interval of time as is actually covered by it in the same interval of time while moving with variable speed.

It is given by the ratio of the total distance traveled by the body to the total time taken by it.

i.e. Average speed =Total distance traveled/Total time taken

**5. Instantaneous Speed:** When a body is moving with variable speed, then, its speed at any instant of time is known as its instantaneous speed.

If a body travels a very small distance Ds in a very small interval of time Dt, then its

Instantaneous speed = limit time tends to 0(ds/dt)

**Numerical**: Try to solve the following numerical and share your answer in the comments section:

If a car travels at a uniform speed of 60 Km per hour in first 40 minutes and then 70 KM per hour in next 30 minutes. Calculate the average speed.

I hope you have understood the difference between speed, uniform speed, variable speed, average speed, and instantaneous speed.

Great