1. Problem-Solving Strategy for Unit Conversions
Teaching a specific method and need to evaluate student understanding of method
Dimensional analysis

2. How many kilograms are in 150 lbs?
Dimensional analysis
Problem-solving strategy to convert measurements in one unit to an equivalent quantity in another unit
How many kilograms are in 150 lbs?
How many calories are in 42 joules?
How many inches are in 127 miles?
How many seconds are in 22 days?

3. Conversion factors
Identify the relationship between two values with different units that express the same quantity
Provide the step-by-step directions to go from the starting point to the ending point
1 min = 60 s
1 hr = 60 min
12 in = 1 ft
1 cal = J
1 kg = 2.2 lbs
1 g = 1000 mg

4. Conversion factors
Such factors are ratios and can be expressed as fractions
The fractions may be written in two ways and always equal a value of 1
If you have one dozen eggs, how many eggs do you have?
Therefore, 1 dozen eggs = 12 eggs
12 eggs
1 dz eggs
12 eggs
12 eggs
1 dz eggs
= 1
= 1

5. Dimensional analysis KNOW WHERE YOU ARE GOING KNOW WHERE YOU START
Identify (underline) the unknown in the problem statement.
KNOW WHERE YOU START
Identify (circle) the given in the problem statement.
DRAW THE BRIDGE
Outlines the path to be taken from start to finish
STEP-BY-STEP DIRECTIONS
Determined by the applicable conversion factors.
It’s all in the units!

6. How many kilograms are in 150 lbs?
Dimensional analysis
How many kilograms are in 150 lbs?
What conversion factor applies to this problem?
1 kg = 2.2 lbs
Expressed as fractions:
Write the UNKNOWN, start with the GIVEN, and then draw the BRIDGE to connect the two quantities
1 kg
2.2 lbs
2.2 lbs
1 kg

7. bridges
Bridges provide the structure for the problem-solving strategy of dimensional analysis
STEP-BY-STEP DIRECTIONS
DRAW THE BRIDGE
GIVEN
CONVERSION
FACTOR
UNKNOWN =
KNOW WHERE YOU ARE GOING
KNOW WHERE YOU START

8. How many kilograms are in 150 lbs?
from LBS to KG
How many kilograms are in 150 lbs?
1 kg = 2.2 lbs
STEP-BY-STEP DIRECTIONS
DRAW THE BRIDGE
GIVEN
CONVERSION
FACTOR
1 kg
150 lbs
kilograms =
UNKNOWN =
2.2 lbs
KNOW WHERE YOU ARE GOING
KNOW WHERE YOU START

9. Now, it’s time for the math.
from LBS to KG
How many kilograms are in 150 lbs?
When the only unit left standing
matches the unknown,
the bridge is complete.
1 kg
150 lbs
kilograms =
2.2 lbs
Now, it’s time for the math.

10. from LBS to KG 1 kg 150 lbs kilograms = 2.2 lbs kg
MULTIPLY all numbers on the top of the bridge
150 x 1 = 150
DIVIDE by each number on the bottom
150 / 2.2 = kg
The unit left standing is the unit of the answer:
CHECK number of significant figures in GIVENs and express answers to same number of SF
ROUND to 2 SF  68 kg

11. Dimensional analysis
How many calories are in 42 joules?
1 calorie = joules
How many inches are in 127 miles?
12 inches = 1 foot
5,280 feet = 1 mile
How many seconds are in 22 days?
60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day