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Appendix D. Units of Measure

Table D.0.1. Distance

Unit	Stands For	Definition	Roughly
m	meter	the distance light travels in \(\sfrac{1}{299792458}\) of a second	half the height of a typical doorway
mm	millimeter	exactly \(\sfrac{1}{1000}\) of a meter	the thickness of a credit card
cm	centimeter	exactly \(\sfrac{1}{100}\) of a meter	the width of your pinky finger
km	kilometer	exactly \(1000\) meters	in parts of Portland where the city blocks are square, about \(12.5\) blocks
in	inch	exactly \(0.0254\) meters	the diameter of a bottle cap
ft	foot	exactly \(12\) inches	the exterior length of an average adult male’s shoe
mi	mile	exactly \(5280\) feet	in parts of Portland where the city blocks are square, about \(20\) blocks

Table D.0.2. Area

Unit	Stands For	Definition	Roughly
cm²	square centimeter	the area of a square whose sides are each one centimeter	a little less than the circular area of a new pencil eraser
in²	square inch	the area of a square whose sides are each one inch	the area of a photograph on an ID card

Table D.0.3. Volume

Unit	Stands For	Definition	Roughly
cm³	cubic centimeter	the volume of a cube whose sides are each one centimeter	the volume of a blueberry
L	liter	exactly \(1000\) cubic centimeters	a bottle of wine is \(\sfrac{3}{4}\) of a liter
mL	milliliter	exactly \(1\) cubic centimeter; \(\sfrac{1}{1000}\) of a liter	the volume of a blueberry
in³	cubic inch	the volume of a cube whose sides are each one inch	the volume of a shelled whole walnut
gal	gallon	exactly \(231\) cubic inches	the volume of the larger type of plastic milk containers sold in supermarkets

Table D.0.4. Time

Unit	Stands For	Definition	Roughly
s	second	the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom	the time it takes you to say the phrase “differential calculus”
min	minute	exactly \(60\) seconds	how long it takes to microwave a full dinner plate from the refrigerator
h	hour	exactly \(3600\) seconds; exactly \(60\) minutes	the length of one episode of a premium cable television show

Table D.0.5. Speed

Unit	Stands For	Definition	Roughly
mph	mile per hour	exactly one mile per hour	a typical walking speed is about three miles per hour

Table D.0.6. Mass

Unit	Stands For	Definition	Roughly
kg	kilogram	the mass of a certain cylindrical object made of a platinum-iridium alloy called the International Prototype of the Kilogram, which is stored in Sèvres, France	the mass of a \(500\)-page paperback book
mg	milligram	exactly \(\sfrac{1}{1000000}\) of a kilogram	the mass of a small snowflake

Table D.0.7. Angle

Unit	Stands For	Definition	Roughly
rad	radian	the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle	a little less than the angles on an equilateral triangle
°	degree	the angle subtended at the center of a circle by an arc whose length is \(\sfrac{1}{360}\) the circumference of the circle	a very small angle; if you could look directly at the bottom of the sun and then move your eyes to look at the top of the sun, you would have moved your eyes about half of one degree

Table D.0.8. Force

Unit	Stands For	Definition	Roughly
N	newton	the force needed to accelerate one kilogram from rest up to a speed of one meter per second with one second of time	if you hold an apple in the palm of your hand, it applies about two newtons of force

Table D.0.9. Power

Unit	Stands For	Definition	Roughly
kW	kilowatt	the power to transfer one thousand joules of energy in one second (one joule is the amount of energy used when one newton of force pushes an object one meter)	the power used by a nicer microwave oven