Physics Fall 2012

 When given a problem like this: 1 x 2 = __ 5 3 how do you solve it?  You multiply straight across!  Do this one on your notes: 3 x 3 = __ 2 4

 What about if you are given this problem: 3 x 2 = __ 4 3  You could multiply straight across and then simplify…  or you could cancel out first to make the problem easier

 Turn to your neighbor and briefly discuss what it means to convert ◦ To convert means to change from one to another ◦ But what are we converting between?  Usually from one unit to another  A unit is a word or abbreviation that comes after the number and describes what that number means  Turn to a new neighbor and briefly discuss why you think it is important to include units with numbers 100 Vs100 dollars vs 100 centsvs 100 miles

 How many shoes do you have if you have 6 pairs of shoes? ◦ How did you figure out that you would have 12 shoes?  How many roses do you have if you are given 4 dozen roses? ◦ How did you figure out that there would be 48 roses?  The fact that there are 2 shoes in a pair of shoes or 12 roses in a dozen roses represent a conversion factor ◦ fractions in which the numerator is equal to the denominator, but the units are different 2 shoes12 roses 1 pair shoes1 dozen roses Discuss with a neighbor some other conversion factors you know of

 Use a conversion factor to convert 3 hours into minutes: 1.What is the conversion factor?  There are 60 minutes in an hour so: 1hr or 60 min 60 min I hr 2.Set up the problem 3 hr x ______ = ______ min 1 *** remember, you want to cancel hours and be left with minutes, so which of the two conversion factors will you use?

 Use a conversion factor to convert 360 minutes into hours: 1. What is the conversion factor? 2. Set up the problem

 Use a conversion factor to convert 96 inches into feet:

 Convert 3 yards into inches

 METRICS!!!! ◦ Turn to a neighbor and discuss what you remember/know about metrics ◦ Used for different scientific measurements ◦ Based on the number “10” ◦ Base units:  Mass – gram  Volume – liter  Distance (length) - meter

 Prefixes are words or parts of words that come “before” another word or word part  Metric prefixes: ◦ Kilo (K) = 1000 m ◦ Hecto (H) = 100 m ◦ Deca (D) = 10 m ◦ Base unit = 1 m ◦ deci (d) = 1/10 m ◦ centi (c) = 1/100 m ◦ milli (m) = 1/1000 m  To help you remember the prefixes in order: King Henry Died by Drinking Chocolate Milk

 Up to this point, you have probably converted between the metric prefixes by simply moving the decimal, right? ◦ Not anymore! ◦ Now, you must use/show the correct conversion factors when converting between the various prefixes – this is called dimensional analysis ◦ Conversion factors examples: 1 Km or m1000 mm or m 1000m Km 1 m cm cm or m m cm

 Convert 3.5 m to cm 1. What is the correct conversion factor? 1m or 100 cm 100 cm 1m 2. Solve the problem 3.5 m x 100 cm = ________ cm 1 1 m ** Which conversion factor will allow you to correctly cancel your starting units and leave you with the correct ending units? **

 Covert 2.56 mm to m 1. What is the correct conversion factor? 2. Set up the problem and solve

 Convert 3.4 Km to m

 Convert 1.25 Km to cm  Can you go directly from Km to cm? ◦ No, you have to do this in two steps so you need two conversion factors 1. 1 Km or 1000 m 1000m 1 Km 2. 1 m or 100 cm 100 cm 1 m  Solve the problem 1.25 Km x 1000 m x 100 cm = 1 1 Km I m ** Which conversion factor will allow you to correctly cancel your starting units and leave you with the correct ending units? **

 Covert 3.2 mm to Km 1. What is the correct conversion factor? 2. Set up the problem and solve

 Convert 93.2 cm to m

 Complete the conversion worksheet that will be passed out

 So let’s make it a bit harder ◦ Can you convert 8km/hr into m/s? ◦ Of course you can – this is called a double conversion  Where you are converting two different units in the same problem  The key to solving these is to convert the units separately 8Km x m x hr x min = m/s 1 hr Km mins

 Convert 575 Km/hr to cm/min 575Km x x x = cm/min 1 hr

 Convert 2500 cm/sec m/min