Watch any car for one minute. It moves off from a light, settles to a cruise, swings through a corner, brakes for a crossing. Hardly any of that minute is spent at one steady velocity.

This topic is about changing velocity. You will learn the name physics gives it, the equation and the unit that measure it, and the sign rules that say whether a motion is speeding up or slowing down.

Nine lessons, and each teaches one skill. The first asks a simpler question than you might expect: what counts as a change in velocity at all?

The last few lessons turned a journey's positions into one picture. This set of lessons draws a new picture of the same kind of journey: the object's velocity, moment by moment. One line on one pair of axes is about to answer four different questions: how fast, which way, speeding up or slowing down, and where the object ends up. How can a single line carry all of that?

One motion can be told three ways: where the object is, how fast it moves, and how quickly its velocity changes. You can already read the first two graphs. This topic adds the third, and then makes all three tell one story on a shared clock.