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
Slide 4
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 = 1 100 cm 1 m = 100 cm 1 m1 m1 m1
m 1 = 1 m1 m 1 m = Conversion factors = 100 cm 1 m1 m
Slide 5
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.
Slide 6
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 1 g1000 mg =mg 1 000 000 g 1 g 2 g 1 g =mg 1 000 000 g 2 g =mg 2
g 1 g1000 mg = 0.002mg 1 000 000 g 1 g
Slide 7
Example: Given: 60 km/hr Want:cm/s 60 km1000 m100 cm1 hr1 min
=1666.67 cm/s 1 hr1 km1 m60 min60 s 60 km = cm/s 1 hr 60 km1000 m =
cm/s 1 hr1 km 60 km1000 m100 cm = cm/s 1 hr1 km1 m 60 km1000 m100
cm1 hr = cm/s 1 hr1 km1 m60 min 60 km1000 m100 cm1 hr1 min = cm/s 1
hr1 km1 m60 min60 s
Slide 8
Example: Example: You are driving 65 mph How many feet do you
travel in this time? 1 s =feet 65 miles or 1 hour 65 miles 1 hour
and take your eyes off the road for Just a Second. 1 s1 min =feet
60 s 1 s1 min1 hour =feet 60 s60 min 1 s1 min1 hour65 miles =feet
60 s60 min1 hour 1 s1 min1 hour65 miles5280 ft =feet 60 s60 min1
hour1 mile 1 s1 min1 hour65 miles5280 ft = 95.333 feet 60 s60 min1
hour1 mile
Slide 9
1 inch = 2.54 cm 2.20 lb =1 kg 30 m100 cm1 inch1 foot1 mile
=0.018641 miles 1m2.54 cm12 inch5280 feet 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 1500 yd3 feet1 mile =0.85227 miles 1
yd5280 feet 206 mi5280 feet12 inch2.54 cm1 m =331524.864 m 1mi1
foot1 inch100 cm 34 kg2.2o lbs =74.8 lbs 1 kg 34 lb1 kg =15.4545 kg
2.2o lbs
Slide 10
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
Slide 11
Accurate or Precise?!?!?
Slide 12
PRECISIONACCURACY 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
Slide 13
Consider the three sets of data below that have been recorded
after measuring a piece of wire that was exactly 6.000 cm long. SET
XSET YSET Z 5.864 cm6.002 cm5.872 cm 5.878 cm6.004 cm5.868 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?
Slide 14
Precise or Accurate?!?!? A nickel has a mass of 5.0 g. You
measure it 4 times: 1.1.05 g 2.10.13 g 3.6.28 g 4.0.92 g 1.10.62 g
2.10.70 g 3.10.69 g 4.10.65 g 1.4.91 g 2.5.00 g 3.5.09 g 4.4.99
g
