UNIT II.1Unit Conversions

II.1 UNIT CONVERSIONS• You MUST learn and use the unit conversion method (not

your own method!)

• A CONVERSION FACTOR: is a fractional expression relating or connecting two different units.

II.1 UNIT CONVERSIONS• Example 1: There are 60 seconds in 1 minute. In

statement form:•

• The conversion factor relates 2 units (minutes to seconds).

II.1 UNIT CONVERSIONS• Example 2: $1.44 per dozen eggs.

• Conversion Factors:

• Conversion factors do not change the VALUE of something, ever….

• We simply use them to change from one unit to another!

II. 1 UNIT CONVERSIONS

THE UNIT CONVERSION METHOD

•We need 3 important pieces of information:

•Desired amount and units ( what we want )•Initial amount and units ( what we know )•Conversion factor (relating the initial units to units of unknown)

II. 1 UNIT CONVERSIONS• Example 3: How many seconds are in 20 minutes?

II.1 UNIT CONVERSIONS• Example 4: If a car can go 90km in 1 h, how far can the

car go in 6.5 h?

II.1 UNIT CONVERSIONS• Example 5: If the price of gas is $1.10 per liter (l), how

much will it cost to fill a 40 liter tank?

II.1 UNIT CONVERSIONS

HOW TO PUT EVERYTHING TOGETHER

• The general form of a unit conversion calculation is:

(wanted amount) = ( Initial amount) x (Conversion factor)

II.1 UNIT CONVERSIONS• Example 6 • a. If 0.200 mL of gold has a mass of 3.86 g, what

is the mass of 5.00 mL of gold?

II.1 UNIT CONVERSIONS• *Important: Always ask yourself “which way do I have to

write the conversion factor so that my units cancel properly?”

• b. If 0.200 mL of gold has a mass of 3.86 g, what is the volume occupied by 100.0 g of gold?

II.1 UNIT CONVERSIONSSUMMARY• Identify wanted/desired amount and its units (put on left

side of = sign).

• Identify the initial amount and its units (put on right side of = sign).

• 3. Identify conversion factor. (Multiply initial amount by conversion factor in such a way that one of the units cancels. You want to be left with units of wanted amount!)

• 4. Complete the problem by multiplying and/or dividing

• Practice Questions:

• Hebden,

• p 11 Exercise 1. a, c, e, g, i

• p 14. Exercise 2. b, d, f, h, j

II.1 UNIT CONVERSIONSMultiple Unit Conversions • We can solve problems that require more than one conversion

factor.

oExample: • If eggs are $1.44 per dozen, and if there are 12 eggs in a

dozen, how many individual eggs can be bought for $4.32?

II. 1 UNIT CONVERSIONS• EX: The automobile gas tank of a Canadian tourist holds 39.5 l

of gas. If 1 L of gas is equal to 0.264 gal in the USA (“gal” is the symbol for “gallon”, a measure of volume used in the US), and gas is $1.26/gal in Dallas, Texas, how much will it cost the tourist to fill his gas tank in Dallas?

• Hebden, p 15 Exercises 3 - 10