Åk 6–9
3.1 Velocity and Speed
There are different types of speeds.  Common to them all is that they describe something that happened during a certain time.

An example is reading speed when you read a number of words during a minute or pages during an hour.

In mathematics and physics, velocity and speed describe hour far something, for example an object, move during a certain time.

Imagine that it takes 10 minutes for you to get to school.  For your little brother it takes 20 minutes to walk to same distance.  You have walked twice as fast and have therefore a greater speed than your brother.

Is there a difference between velocity and speed?
Normally we use the concepts velocity and speed for the same thing.  In physics though, we differ between the concepts.

Speed: The direction of for example and object does not matter.
Velocity: Here it is important which movement and direction an object has.

It doesn’t matter greatly which of the concepts you use when talking casually.  In this text, we will use both concepts when it’s natural to use them.

Calculating Velocity
Velocity is about how far an object has moved during a certain time.

Imagine that you have moved 10 meters in 5 seconds with the same speed.

How far have you moved for every second?

For every second you have moved 2 meters.

You velocity is then 2 meters every second: 2 m/s.

You can describe and calculate velocity with the formula v = d ÷ t and show it in a graph in a coordintate system.

Velocity is abbreviated v .
Time is abbreviated t.
Distance is abbreviated d.

Line A describes how Alicia moves with a constant (same) velocity.

Line B describes how Bernie moves with a constant (same) velocity.

Line A shows that Alicia has travelled 1 m after 1 s, 2 m after 2 s and 4 m after 4 s. This means that Alicia’s velocity is:

v = 1 m/s

Line B shows that Bernie has travelled 2 m after 1 s and 4 m after 2 s. This means that Bernie’s velocity is:

v = 2 m/s