### Speed

**The distance travelled either a straight line or a circular line by a rigid body in a unit time is known as the speed of the rigid body. **

Direction is not required for mention speed of a rigid body. It is a **scalar quantity**. A car is moving 20 kilometres / hour. Here 20 km / hour is the speed.

i.e. if a rigid body moves s distance in t second then the speed of the rigid body will be s/t.

### Units of the speed

MKS or IS method:metre / second (ms^{-1})

CGS method : centimetre / seconds (cm s^{-1})

FPS method : foot / seconds ( fs^{-1})

Kinds of speed

Speeds are divided into four types

If the body is covering equal distance in equal interval of time in any direction, then that speed is known as uniform speed.*Uniform speed:*

For Examples, if a car travels 60 km / HR. That is 1km / minute. Then we can say that the car has a uniform speed of 6okm / HR. Or 1 km / min.

If the body is covered unequal distance in equal interval of time in any direction, then that speed is known as non-uniform speed or variable speed.*Non-uniformed speed Or variable speed:*

For examples, if a car travels 30km in 30 minutes, 25 km in next 30 minutes, 20 km in next 30 minutes. Then we can say that the car has a non-uniform speed.

If a rigid body changes its speed continuously with time, then the speed of the rigid body at any instant or any moment is known as instantaneous speed.*Instantaneous Speed:*

When a body travel with a variable speed, then the average speed will be calculated by dividing the total distance cover by the body and the total time is taken.*Average Speed:*