# Journeys calculated

### Making changes

Tracks can be predicted. Split the journey into legs each one second long. To know where you’ll end up after each leg you need to know how fast you’re going(how many metres in that second), and in which direction. That’s the velocity, shown by an arrow. You also need to know a second measure, the interval (for how many seconds you expect to keep up that velocity). From where you expect to end up, predict the next leg in exactly the same way, again choosing a velocity.

For each leg, the velocity sets the leg length and direction. In this case each leg lasts for one second(the interval of the leg). Over many legs, you build up a track even if you’re flying.

### Another varying journey

Another journey, now a human walking. Again you construct a track from legs – an accumulation.

You can predict the track from where you start and the sequence of velocities. You need a list of velocities and intervals(how long you expect to keep up each velocity).

You can use the same information to record a track: just log the velocities for every second. Now you need a list of velocities and durations(how long you did keep up each velocity).