Speed vs Velocity

• The terms speed and velocity are often used interchangeably, but in physics there is an important difference in their meaning.

• Speed is a measure of the rate at which distance changes.

• It is a scalar quantity, with a magnitude but no direction.

• Speed is calculated using the formula:

• Velocity is a measure of the rate at which displacement changes.

• It is a vector quantity, with a magnitude as well as a direction.

• Velocity is calculated using the formula:

• Since velocity is a vector quantity, every time a moving object has a change in direction, it also has a change in velocity, even if it is travelling at a constant speed.

• For example, an object travelling in a circular motion at a constant speed has a constantly changing velocity as it is constantly changing direction.

• Only an object travelling at a constant speed in the same direction has a constant velocity.

• Measuring velocity can be quite complex. In this unit we will mostly refer to the movement of an object in terms of speed rather than velocity.

A merry-go-round moves at a constant speed but has a constantly changing velocity.

(Image: PublicDomainPictures, Pixabay)