## Converting between different system of units

Unit conversion is an important skill – a failure to convert from imperial to metric units caused the loss of the . Typically, in physics, we measure speed in meters/second (m/s), but in the outside world other units, like miles/hour (mi/hr) are much more common. How do we convert between them?

1 mi/hr = x m/s

We want to find the unknown “x” – it is the conversion factor between mi/hr and m/s.

To proceed, we need to multiply the left hand side by quantities that equal one (so as to not change the value) but allow us to change the units to the ones we require. 1 hour and 60 minutes are the same thing, so 1hr/60mins = 1 (or, in English one hours has exactly one group of 60 minutes within it). Similarly, 1min/60s = 1 and 1610m/1mi = 1

1 mi/hr * 1hr/60mins * 1min/60s * 1610m/1mi = 1610/3600 (mi/mi) (hr/hr) (min/min) m/s = 0.45m/s

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