# 1.2 Speed, velocity and acceleration

Speed

The speed of a body is the rate of distance traveled in unit time interval. It is a scalar quantity.

s=d/t

S.I unit : *m/s.*

**Uniform speed**

A body is said to be moving at uniform speed if it covers equal distances in equal time intervals.

**Instantaneous speed**

If the speed of a body changes continuously with time, its speed at any instant is known as the Instantaneous speed.

**Average speed**

Most objects speed up and slow down as they travel. An object’s ‘average speed’ can be calculated by dividing the total distance traveled by the total time taken.

The ratio of the total distance traveled by the body to the total time of journey is called the average speed.

Average distance=Total Distance/Total Time

Velocity

It is the rate of distance traveled with time in a specified direction. In other words, it is the distance covered by the body in a specified direction in unit time interval.

Thus, the rate of change of displacement is called velocity.

It is a vector quantity.

S.I units: *m/s.*

A velocity can have a minus sign. This tells you that the object is traveling in the opposite direction. So a velocity of -278 m/s upwards is actually a velocity of 278 m/s downwards.

**Uniform velocity**

If a body travels equal distances in equal intervals of time along with a particular direction, the body is said to be moving with a uniform velocity.

Acceleration

It is the rate of change of velocity.

Acceleration=u-v/∆t

where u- initial velocity, v-final velocity and Δ t change in time.

For example, if an object’s velocity changes from 10 meters per second to 20 meters per second in five seconds, its acceleration

a=(20-10)/5=2 m/s^{2}

**Differences between Speed and Velocity**

Speed | Velocity | |

1. | The distance traveled by a moving object in unit time is called its speed | Te distance traveled by a moving object in unit time in a particular direction is called its velocity |

2. | It is a scalar quantity | It is a vector quantity |

3 | Speed can be positive or zero | Velocity can be positive, negative or zero |

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