Factor-Label Method Section 2.6 p 28-33

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

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

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.

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 = 0.002 mg 1 000 000 g 2 g 2 g 1 g = mg 1 000 000 g 2 g 1 g 1000 mg = mg 1 000 000 g 2 g = mg

Example: Given: 60 km/hr Want: cm/s 1 min = 1666.67 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

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 = 95.333 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

Customary and SI System To Convert between the Customary and SI System 1 inch = 2.54 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 = 331524.864 m 1mi 1 foot 1 inch 100 cm 30 m 100 cm 1 inch 1 foot 1 mile = 0.018641 miles 1m 2.54 cm 12 inch 5280 feet 1500 yd 3 feet 1 mile = 0.85227 miles 1 yd 5280 feet 34 lb 1 kg = 15.4545 kg 2.2o lbs 34 kg 2.2o lbs = 74.8 lbs 1 kg

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

Accurate or Precise?!?!?

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

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 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

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