Let the units Let the units work for work for

you!you!

Step 1: Write down the unit you Step 1: Write down the unit you need for your answer on the right need for your answer on the right

side of your paperside of your paper

Step 2: Write down the unit you are Step 2: Write down the unit you are starting with on the left side of your starting with on the left side of your

paperpaper

Step 3: Try putting in equivalent Step 3: Try putting in equivalent units until they all cancel and give units until they all cancel and give

you what you wantyou what you want

Examples of equivalent units

1 min60 sec

5280 ftmile

12 in ft

60 minhr

1 yard3 ft

1m3.3 ft

55 mi88.5 km

1 mile1609m

1 yr365.25 days

ExampleIn our “constant force” experiment we used a weight to pull cars across the floor. We were surprised to see how

much they accelerated (changed speed)

Some of the cars reached speeds of 150cm/secSome of the cars reached speeds of 150cm/sec

That sounds fast, but what is that in That sounds fast, but what is that in mi/hr?mi/hr?

Step 1- I want an answer in mi/hr, so I will put that on the left

Step 2- I have cm/sec so I will put that on the left

cmsec

hrmi

Step 3- add equivalencies, one at a time until you can convert the units. I usually leave the numbers out untilI determine what units will work

cmsec xx == cm

hr

cm

hrxx

mcm

mimxx

hrmi==

sec1 hr

Remember you are trying to change cm/sec into mi/hrRemember you are trying to change cm/sec into mi/hr

150 cmsec xx == 540000cm

hr

540000cm

hrxx 1 m

100 cm1mi

1609 mxx

hr3.36 mi

==

3600 sec1 hr

Remember you are trying to change cm/sec into mi/hrRemember you are trying to change cm/sec into mi/hr