Concept preview

What you will be able to do

1. 01Build a conversion factor from an equivalence and use it to change units
2. 02Convert compound units such as km/h to m/s by cancelling units
3. 03Use dimensional analysis to check whether an equation can be correct

If I ask 'how many minutes is 2 hours?', you instantly say 120 — you multiplied by 60. That's a unit conversion, and physics just makes the trick reliable enough that you never get it upside down. The secret is deceptively simple: to change units, you multiply by a clever form of the number 1.