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Factor-Label Method. Section 2.6 p 28-33. 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.
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Factor-Label Method Section 2.6 p 28-33
Based on Conversion factors, which are relationships between the units. • A conversion factoris 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.
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
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 How can 65 mph be used? It’s a conversion factor
To Convert between the Customary and SI System 1 inch = 2.54 cm2.20 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
In the lab we need to determine the reliability of our measurements2 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
Consider the three sets of data below that have been recorded after measuring a piece of wire that was exactly 6.000 cm long. • 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