1.4 Acceleration

Make sure you feel secure in your knowledge of velocity from the previous module, because you’re going to need that foundation for what we do next.

Key Ideas:

• Velocity is a vector. It’s easiest to think of velocity as a speed and direction lumped together in a single measurement.

• Acceleration is defined as the change of velocity over time.

• Velocity can change because the speed changes, or because the direction changes, or because both speed and direction change. Therefore, any change in the velocity is an acceleration.

TextbookSection: 2.4 in OpenStax College Physics 2e

This is going to seem like a short module, especially compared with the ones around it. However, acceleration is so important that it is worth spending time just looking closely at its definition and seeing how the math and the physical reality combine.

First, a definition in words:

Acceleration = [change of velocity] / [change of time]

Acceleration has dimensions of [velocity units] / [time units] and since velocity has dimensions of [distance units] / [time units] we end up with an interesting situation: Acceleration has dimensions of

[distance units] / [time units] / [time units]

The key to recognizing an acceleration when you see one is that there will be two time units in the denominator. This may appear in a number of ways.

The most common is