Unit Conversions And the SI system

Unit Conversion Conversions are part of daily life Hours worked → $ on paycheck Travel distance → Minutes of driving Kind of cell phone → Cost of calling plan

Unit Conversion Both things are equivalent, but you change them in order to make better sense of the information. Def: Conversion- changing a number from one kind of unit to another in order to use it in an equation.

Why convert? In physics we take basic measurements of time, mass, and length all the time. Before we can do ANY math, these measurements HAVE to be in these SI units: Time- seconds (s) Mass- kilogram (kg) Length- meter (m)

Common Conversions Time: 1 min = 60 s 1 hr = 3600 s 1 day = 86,400 s Mass: 2.2 lb = 1kg Length: 1 in = 2.54 cm 1 mi = 5280 ft

How do we convert? Another way to write that two things are equivalent is to write them as a fraction. Example: 1 in = 2.54 cm is the same as and also

Conversion Factors Writing an equivalency like this is called a Conversion Factor. This is what we use to go from one unit to another.

Conversion Factors 1 min = 60 s or 1 hr = 3600 s or Any of these can be written as conversion factors. (It doesn’t matter which number is on the top and which is on the bottom) 1 min = 60 s or 1 hr = 3600 s or 1 day = 86,400 s or 2.2 lb = 1kg or 1 in = 2.54 cm or 1 mi = 5280 ft or

Using Conversion Factors Example: Convert 5 in to centimeters. Step 1: Write the number down WITH UNITS. 5 in

Using Conversion Factors Example: Convert 5 in to centimeters. Step 2: Set up a “T chart”. 5 in

Using Conversion Factors Example: Convert 5 in to centimeters. Step 3: Find a conversion factor with the same units IN THE DENOMINATOR. 5 in 2.54cm 1 in

Using Conversion Factors Example: Convert 5 in to centimeters. Step 4: Cancel units (NOT numbers) 5 in 2.54cm 1 in =

Using Conversion Factors Example: Convert 5 in to centimeters. Step 5: Simplify and keep the units that AREN’T cancelled out 5 in 2.54cm 5 * 2.54 cm 12.7 cm 1 in 1 = =

Practice On a scratch piece of paper, perform the following conversions: Convert 3 days into seconds. Convert 600 feet into miles. Convert 195lbs into kilograms.

Practice On a scratch piece of paper, perform the following conversions: Convert 3 days into seconds. 259,200s Convert 600 feet into miles. Convert 195lbs into kilograms.

Practice On a scratch piece of paper, perform the following conversions: Convert 3 days into seconds. 259,200s Convert 600 feet into miles. 0.11 mi Convert 195lbs into kilograms.

Practice On a scratch piece of paper, perform the following conversions: Convert 3 days into seconds. 259,200s Convert 600 feet into miles. 0.11 mi Convert 195lbs into kilograms. 88.63 kg

Two Step Conversions Some conversions may require two conversion factors to complete. Example: Convert 1 mi into inches. 1mi

Two Step Conversions Some conversions may require two conversion factors to complete. Example: Convert 1 mi into inches. 1mi 5280ft 1mi

Two Step Conversions Some conversions may require two conversion factors to complete. Example: Convert 1 mi into inches. 1mi 5280ft 12in 1mi 1ft

Two Step Conversions Some conversions may require two conversion factors to complete. Example: Convert 1 mi into inches. 1mi 5280ft 12in 1*5280*12 in 1mi 1ft 1*1 =

Two Step Conversions Some conversions may require two conversion factors to complete. Example: Convert 1 mi into inches. 1mi 5280ft 12in 1*5280*12 in 63,360 in 1mi 1ft 1*1 = =

Practice Perform the following conversion: Convert .5 years to seconds. Convert 1 ton to kilograms (1 ton is 2000 lbs).

Practice Perform the following conversion: Convert .5 years to seconds. 15,768,000 s Convert 1 ton to kilograms (1 ton is 2000 lbs).

Practice Perform the following conversion: Convert .5 years to seconds. 15,768,000 s Convert 1 ton to kilograms (1 ton is 2000 lbs). 909.1 kg

SI Prefixes These are some common prefixes to the SI units that can help you come up with more conversion factors: Centi: 1/100th Ex: 100 cm = 1 m Milli: 1/1000th Ex: 1000 ms = 1 s Kilo: 1000 Ex: 1 kg = 1000 g

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s.

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft h 1mi

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in h 1mi 1ft

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in 2.54cm h 1mi 1ft 1in

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in 2.54cm 1m h 1mi 1ft 1in 100cm

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in 2.54cm 1m 1h h 1mi 1ft 1in 100cm 3600s

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in 2.54cm 1m 1h h 1mi 1ft 1in 100cm 3600s 10*5280*12*2.54*1*1 m 1,609,344 m 1*1*1*100*3600 s 360,000 s = =

Converting Multi Units Sometimes we have to convert two thing in one problem before doing the math. Example: Convert 10 mph into m/s. 10 mi 5280ft 12in 2.54cm 1m 1h h 1mi 1ft 1in 100cm 3600s 10*5280*12*2.54*1*1 m 1,609,344 m 4.47m/s 1*1*1*100*3600 s 360,000 s = = =

Practice Using your notes as a guide, complete the classwork assignment on unit conversion.