Do now

• 1) Round these numbers– 19870 to 2 sig figs– 0.00598 to 1 SF

• 2) What would the units be for the following problem– 12 g / 3 ml = 4 ???

• 3) Put .002104 into scientific notation

Period 4 Test:

• This upcoming Wednesday!• I am here after school on

Tuesday…

Sci. Notation ‘Quiz’

Conversions!

• Lets start easy• 2 minutes seconds…• 3 yards feet• 24 inches feet• How did you do all these?

Conversion Factors

• When converting from one unit to another you use a conversion factor:

• 12 in/foot• 24 inches feet• 24 in / (12 inches/foot) 2 feet• 2 minutes seconds• 2 minutes x 60 seconds/minute 120 seconds

Its all about units!

• You first need to figure out what conversion factor your going to use

• Then how you will use it so that your desired units are left and everything else cancels out:

• 24 inches feet • Conversion factor: 12 inches/foot• Multiply or divide?

12 inches/foot

• We want inches to cancel out to get feet…• For that to happen, we need to divide• 24 inches / (12 inches/foot)keep change flip• 24 inches x 1ft/12 inches• 24 ft / 12• 2 ft

How to Determine if you need to multiply or divide

• If the unit you want to cancel out is on the bottom of the CF, multiply– ( a * b/a = b)

• If the unit you want to cancel out is on the top, divide– ( a / [a/b] = b)

Converting Prefixes

• Often we will have to convert g to mg, or kg, or ml to l and vice versa.

• In order to do so we need to look at the values of the prefixes (Ref. Table C)

Conversion

• To convert a measurement from one metric unit to another, you must know the difference in magnitude between the two prefixes and use that difference to create a conversion factor which will look like:

How do you figure that out?

• You can simply look to Table C of the RT’s to determine magnitude diff.

• If there is no prefix then the power of ten is 100

What is the conversion factor for m to km?

• No prefix is 100

• k is 103

• Difference is 3 powers of 10 (=1000)

• 1000 m/km or 1000 km/m?

• The smaller one always gets the number

• 1000 m/km

cg mg

• 10-2 and 10-3

• Difference of 1 power of ten (10)

• Which is smaller?• 10 mg/cg

mm km

• 10-3 and 103

• Difference of 6 powers of ten (1,000,000)

• Which is smaller?• 1,000,000 mm/km

OK, then what?

• Going to use the conversion factor (either multiplying or dividing depending on the need)

• Example: 2km is how many meters?• Conversion factor: 1000 m/km• Need km to cancel out, and its on the bottom

of the CF so we….• 2 km x 1000 m/km = 2000 m

What if it was the other way?

• Converting 2000 m to km• Conversion factor 1000 m/km• Want m to cancel out and is on top of the CF

so we…• 2000m / (1000m/km) = 2 km

Convert 20.0 mm to m

• mm = 10-3 m = 100

• 3 powers of ten different = 1000• 1000 mm/m• 20.0 mm / (1000mm/m) = 0.0200 m

How many mm are there in 120 km?

• mm= 10-3 km= 103

• Difference of 6 powers of ten• 1000000 mm/km• 120 km x 1000000 mm/km = 120000000 mm• Or 1.2 x 108 mm

Dimensional Analysis simplified

1) Determine the Conversion Factor via looking at table c– Remember; the smaller unit gets the number

2) Determine if you need to multiply or divide– If the unit you want to cancel out is on the bottom of

the CF, multiply ( a * b/a = b)– If the unit you want to cancel out is on the top, divide (

a / [a/b] = b)

3) Solve, making sure you have the correct Sig Figs in your final answer

Work on Conversion Homework (p 24-25)

• I will be wandering around helping, raise a hand if you have a question/want me to check what you’ve done so far