How is velocity defined?

Velocity is defined as the covered distance during a certain period of time:

or as a fomula:

In order to measure velocities you need a stopwatch and a measuring tape to measure the distance. Then measure the time your friend needs for covering the distance by foot or bicycle. Then you can calculate the velocity from the formula. Here are some examples:

- Normally a car drives at a speed of 100 km/h (say kilometres per hour).
- The bang of a bullet is propagating at a speed of approx. 330 m/s (say: metres per second).
- In constrast the bullet is racing at a speed of 800 m/s through the air.

What is a constant velocity?

When physicists talk about a constant velocity, they mean a velocity which never changes. So at every point of time during the movement it has got the same value, i.e. 4 km/h. (red line)