Post on 26-Mar-2015
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, 1 min = 60 sec
Conversion Factors:
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, they just change the UNITS.
To change the UNITS, multiply by the CONVERSION FACTOR.
II. 1 UNIT CONVERSIONS
THE UNIT CONVERSION METHOD:
We need 3 important pieces of information: unknown amount and units initial amount and units conversion factor (relating the initial units to
units of unknown)
II. 1 UNIT CONVERSIONS
o Example 3: How many seconds are in 20 minutes?
Unknown amount: Initial amount: Conversion factor:
Solution
** ALWAYS include UNITS in your calculations!
II.1 UNIT CONVERSIONS
o Example 4: If a car can go 90km in 1 h, how far can the car go in 6.5 h?
Unknown amount: Initial amount: Conversion factor:
Solution
II.1 UNIT CONVERSIONS
o Example 5: If the price of gas is $1.10 per liter (l), how much will it cost to fill a 40 liter tank?
Unknown amount: Initial amount: Conversion factor:
Solution
II.1 UNIT CONVERSIONS
HOW TO PUT EVERYTHING TOGETHER
The general form of a unit conversion calculation is:
(Unknown amount) = ( Initial amount) x (Conversion factor)
II.1 UNIT CONVERSIONS
o 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?
Unknown amount: Initial amount: Conversion factor: Solution
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?
Unknown amount: Initial amount: Conversion factor:
Solution
II.1 UNIT CONVERSIONS
SUMMARY Identify unknown 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 cancel. You want to be left with units of unknown amount!)
4. Complete the problem by multiplying and/or dividing amounts of RHS.
ASSIGNMENT
II.1 UNIT CONVERSIONS
Multiple Unit Conversions We can solve problems that require more than
one conversion factor.
o Example: 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?
ANALYZE THE PROBLEM:
Unknown amount: Initial amount: Conversion factors:
II.1 UNIT CONVERSIONS
Solution: we require the connection conversion factor 1 gives the connection:
conversion factor 2 gives the connection:
Combining conversion factors 1 and 2 gives:
II.1 UNIT CONVERSIONS
Solve for unknown amount:
Unknown amount = Initial amount x Conversion factors (1 and 2)
ASSIGNMENT