Todays Agenda Primary and Secondary Physical Quantities and

Today’s Agenda • Primary and Secondary Physical Quantities and Units • Unit Conversion

Standard We Will Use • We will follow the International System of Units – also known as the SI standard – It includes: Distance measured in meters (m) Mass measured in kilograms (kg) Time measured in seconds (s) Charge measured in Coulombs (C) Temperature measured in degrees Kelvin (o K or K) • That means we’ll need to convert other measures to our standard

Fundamental or Primary Quantities • 7 SI base units: those from which all others are derived – – – – meter kilogram second ampere kelvin candela mole (m) (kg) (s) (A) (K) (cd) (mol) length weight time current temperature luminosity molecular quantity Quick in-class exercise: – Identify physical examples, and electrical examples

Derived or Secondary Quantities • “SI derived unit”: derived from base units • Unlimited number of derived units! • Some examples: – – – meter / second squared newton pascal joule volt watt ohm farad henry hertz (N) (Pa) (J) (V) (W) (Ω) (F) (Hz) m/s 2 kg·m / s 2 N / m 2 N·m kg⋅m 2⋅s− 3⋅A− 1 J / s V / A C / V V⋅s / A 1 / s velocity acceleration force pressure energy voltage power resistance capacitance inductance frequency

Commonly used prefixes T G M k tera giga mega kilo 1012 109 106 103 d c d μ n p deci centi milli micro nano pico 10 -1 10 -2 10 -3 10 -6 10 -9 10 -12

What Units Should We Use? • Example distance units: • Example time units:

What Happens If We Mix Units? • Consider the Mars Climate Orbiter that was launched in 1998 (see handout). • It turns out that someone at NASA forgot to convert English units (pounds) to metric units (Newtons) when calculating the necessary rocket thrust to put the craft in orbit around Mars • Guess what happened?

Class Activity #1 a. ) A tractor-trailer truck is traveling at 60 miles per hour eastbound on Interstate 195 towards the North Dartmouth exit. Determine the speed of the truck i. ) in feet per second ii. ) in meters per second iii. ) in kilometers per hour. b. ) What is the maximum legal speed in centimeters per hour in a 55 miles per hour posted speed zone?

Homework for next class • In the textbook, – Read Chapter I (Introduction) – Read Chapter 1