# Speed : Definition,formula,unit and examples

Speed

## What is speed in physics?

“The distance covered by an object in unit time is called its speed”.In other words, the rate at which object is moving is called speed.Unit time may be a second, an hour, a day or a year.It tells us how fast or slow an object is moving.Its formula is given as:

Here S is the distance covered by the object, V is its speed and t is the time taken by it.Distance is a scalar; therefore ‘speed is also a scalar quantity.SI unit of speed is meter per second, other units like kilometre per hour, miles per hour, feet per second are also used.

Most objects or bodies do not move at constant speed.For example, the MRT train starts from rest at a station, moves faster until it reaches a constant (or cruising) speed and then slows down to a stop at the next station.It is, therefore, more useful to define average speed <v> rather than the actual speed v.

Thus:

## Table of speed of some objects:

Moving object | Speed in ms^{-1} | Speed in kmh^{-1} |

Earth rotating around the sun | 30 000 | 108 000 |

Boeing 747B | 300 | 1080 |

Car | 16.7 | 60 |

Sprinter | 10 | 36 |

MRT | 12.5 | 45 |

Walking | 2.5 | 9 |

The speed of sound in air at room temperature is about 330 m ⁄s or about 1200 km/h but the fastest speed is that of light in a vacuum is 3 × 10¤8 m/s.

## Uniform Speed:

“body has uniform speed if it covers equal distances in equal intervals of time however short the interval may be.”

In equation S=v t v is the average speed of a body during time t.It is because the speed of the body may be changing during the time interval t.However, if the speed of a body does not vary and has the same value then the body is said to possess uniform speed.

## Non Uniform Speed:

“A body does not have uniform speed if it does not cover equal distance with an equal interval of time.”

### Find average speed (video)

External sources

- http://www.physicsclassroom.com/class/1DKin/Lesson-1/Speed-and-Velocity

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