Dimensional Analysis

There is a process that can make difficult problems much easier.

You will write these notes on page 9

Step 1

• Determine what you want to know in the END.

1. Think in terms of UNITS.2. Translate into math terms (ie fractions).

• Kilometers per hour would be Kmhr

Step 2

• List out what you already know.1. What is given in the problem2. What conversion factors will you need?

Step 3

• Set up the problem.1. Pick a starting factor from your list (especially if it

has the same units as your end result in the right place).

2. Pick a conversion factor that will cancel out a unit not needed in the end.

3. Continue picking out conversion factors that will cancel out units you don’t want.

4. If you get stuck, look for conversion factors.

Step 4• Do the math operations. Make sure all

unneeded units cancel out.1. Simplify the numbers by cancellation.2. Multiply the top numbers, then divide the result by

each bottom number.3. Double check that you entered numbers into the

calculator correctly and that the answer makes sense.

4. Round your answer to the correct number of significant figures (coming up next class)- basically the answer should show the same level of preciseness as the measures you started with.

Practice

• How many seconds are in a day?• How many hours are in a year?• If you are going 50 miles per hour, how many meters per

second are you traveling?• How much bleach would you need to make a quart of 5

percent bleach solution?• Your car's gas tank holds 18.6 gallons and is one quarter full.

Your car gets 16 miles/gal. You see a sign saying, "Next gas 73 miles." Your often-wrong brother, who is driving, is sure you'll make it without running out of gas.