1. Factor-Label Method
Section 2.6 p 28-33

2. It is a ratio equivalent to 1
Based on Conversion factors, which are relationships between the units.
A conversion factor is used to convert a unit to any other related unit.
The conversion factor is derived from the equivalence statement of the two units.
For example: 1 inch = 2.54 cm.  
It is a ratio equivalent to 1

3. ALWAYS WORK THROUGH THE BASE UNITS!!!!!!!
Example: 1 m = 100 cm
The correct choice is the one that allows the cancellation of the unwanted units.
1 m =
100 cm
1 m =
100 cm
1 m = 1
100 cm 1 =
100 cm
1 m
1 m =
Conversion
factors
100 cm

4. Problem Solving Strategies:
1. Write the known value (given)
2. Draw the baseline (cross)
3. Write the wanted units (units of the answer)
4. Write the necessary conversion factors
If the unit to be eliminated is in the numerator of the given information then that unit should appear in the denominator of the conversion factor, and vice versa.

5. Example: How many milligrams are in 2 micrograms?
Step 1: Write the given.
Step 2: Draw the baseline
 Step 3: Write the wanted units (units of the answer)
 Step 4: Write the conversion factor(s).
SINCE I DO NOT KNOW A DIRECT RELATIONSHIP, I WORK THROUGH THE BASE UNIT
2 g
2 g
1 g
1000 mg = mg g
2 g
2 g
1 g = mg g
2 g
1 g
1000 mg = mg g
2 g = mg

6. Example: Given: 60 km/hr Want: cm/s
1 min =
cm/s
1 km
1 m
60 min
60 s
60 km
1000 m
100 cm
1 hr =
cm/s
1 km
1 m
60 min
60 km
1000 m
100 cm
1 hr
1 min =
cm/s
1 km
1 m
60 min
60 s
60 km
1000 m =
cm/s
1 hr
1 km
60 km =
cm/s
1 hr
60 km
1000 m
100 cm =
cm/s
1 hr
1 km
1 m

7. Example: You are driving 65 mph
and take your eyes off the road for “Just a Second.”
How many feet do you travel in this time?
What is the given?
1 second
1 s
1 min
1 hour
65 miles
5280 ft =
feet
60 s
60 min
1 mile
1 s
1 min
1 hour =
feet
60 s
60 min
1 s
1 min =
feet
60 s
1 s
1 min
1 hour
65 miles =
feet
60 s
60 min
1 s
1 min
1 hour
65 miles
5280 ft =
feet
60 s
60 min
1 mile
1 s =
feet
65 miles or
1 hour
How can 65 mph be used?
It’s a conversion factor

8. Customary and SI System
To Convert between the
Customary and SI System
1 inch = cm 2.20 lb = 1 kg
Convert the following quantities from one unit to another
 30 m to mi
1500 yd to mi
206 mi to m
34 kg to lbs
34 lb to kg
206 mi
5280 feet
12 inch
2.54 cm
1 m = m
1mi
1 foot
1 inch
100 cm
30 m
100 cm
1 inch
1 foot
1 mile =
miles 1m
2.54 cm
12 inch
5280 feet
1500 yd
3 feet
1 mile =
miles
1 yd
5280 feet
34 lb
1 kg = kg
2.2o lbs
34 kg
2.2o lbs =
74.8 lbs
1 kg

9. In the lab we need to determine the reliability of our measurements 2 ways
Accuracy - how close is a measurement to the true or correct value for the quantity.
Percent error
Precision - how close a set of measurements for a quantity are to one another, regardless of whether the measurements are correct.
Significant digits

10. Accurate or Precise?!?!?

11. PRECISION ACCURACY Reproducibility Correctness
Check by repeating measurements
Check by using a different method
Poor precision results from poor technique
Poor accuracy results from procedural or equipment flaws
Significant digits
Percent Error

12. Consider the three sets of data below that have been recorded after measuring a piece of wire that was exactly cm long.
SET X
SET Y
SET Z
5.864 cm
6.002 cm
5.872 cm
5.878 cm
6.004 cm
5.868 cm
Which set of data is the most accurate?
Which set of data is the most precise?
Which set of data is more precise, set X or set Z?
Set Y
Set Z

13. Precise or Accurate?!?!? A nickel has a mass of 5.0 g.
You measure it 4 times:
1.05 g
10.13 g
6.28 g
0.92 g
10.62 g
10.70 g
10.69 g
10.65 g
4.91 g
5.00 g
5.09 g
4.99 g