The fundamental units are the meter, second, kilogram, and Coulomb. They were defined in 1793 as the "Standard International" (SI) units, or "MKS" units.

Quantity Unit Definition Length Meter The Earth's circumference is 40 million meters Time Second There are 86400 seconds in one Earth day Mass Kilogram The mass of a cube of water 10 cm on a side is 1 kilogram Charge Coulomb The force between two charges of one Coulomb each and separated by 1 meter is 9 billion Newtons

Density of water =1000 kg/meter$3$ = 1 g/cm$3$ Density of air = 1.2 kg/meter$3$ = .0012 g/cm$3$

The fundamental units are length, mass, time, and charge, and all other units are derived from these.

Quanity Composition Units Length = X meters Mass = M kg Time = T seconds Charge = C Coulomb Speed = V = X/T Length / Time meters/second Acceleration = A = V/T Speed / Time meters/second^{2}Momentum = Q = M V Mass * Speed kg meters/second Force = F = M A Mass * Acceleration Newtons = kg meters/second^{2}Energy = E = F X Force * Distance Joules = kg meters^{2}/second^{2}Power = P = E/T Energy / Time Watts = kg meters^{2}/second^{3}Area = S = X^{2}Length$2$ meters$2$ Volume = Υ = X^{3}Length$3$ meters$3$ Density = ρ = M/Υ Mass / Volume kg / meters^{2}Pressure = Φ = F/S Force / Area Pascals = Newtons/meter$2$ = Joules/meter$3$ Angular momentum = L = M V X Momentum*Length kg meters$2$/second Torque = Γ = F X Force * Length kg meters$2$/second$2$ Frequency = f = 1/T 1 / Time Hertz = 1/second

Meter = 3.281 feet = 39.37 inches Mile = 5280 feet (exact) = 1609 meters Foot = 12 inches (exact) Inch = 25.4 mm (exact) Minute = 60 seconds (exact) Hour = 60 minutes (exact) Day = 24 hours (exact) Year = 365.25 days Ton = 1000 kg (exact) Kilogram = 1000 grams (exact) = 2.205 pounds (pounds interpreted as mass) Newton = .225 pounds (pounds interpreted as force) Pound = 16 ounces (exact) (interpreted as mass) = .454 kg 4.448 Newtons (Newtons interpreted as force) Ounce = 28.35 grams (ounces interpreted as mass) Meter/second = 2.24 miles/hour Km/hour = .621 miles/hour Miles/hour = 1.609 km/hour Pascal = .0001450 pounds/inch^{2}(pounds interpreted as force) Pound/inch^{2}= 6895 Pascals Bar =101325 Pascals (Atmosphere pressure at sea level) = 14.50 pounds/inch^{2}(pounds interpreted as force) Earth gravity= 9.807 meters/second^{2}= 32.2 feet/second^{2}Standard sheet of paper = 11 x 8.5 inches = 27.94 x 21.59 cm

Meters Earth Earth Light travel radii orbits time (AU) Nucleus 2⋅10$-15$ Atom 2⋅10$-10$ Green light 5.5⋅10$-7$ Neuron .00002 Dime thickness .00135 Dime diameter .0178 Quarter diameter .024 Tennis ball diameter .067 Soccer ball diameter .22 Average person 1.78 Central Park width 800 Mount Everest 8848 Moon radius 1737000 .273 Mars radius 3390000 .532 Earth radius 6371000 1.0 Jupiter radius 6.991⋅10^{7}10.9 Moon distance 3.844⋅10^{8}60.3 .00257 1.5 seconds Sun radius 6.957⋅10^{8}109 .00474 2.3 seconds Earth orbit 1.496⋅10^{11}23481 1.0 8 minutes Jupiter orbit 5.2 40 minutes Neptune orbit 30.1 3 days Light year 9.461⋅10^{15}63241 1 year Alpha Centauri 4.4 years Nearest star Galaxy thickness 1000 years Galaxy center 27200 years Galaxy diameter 100000 years Andromeda distance 2.5 million years Virgo cluster distance 54 million years Size of universe 14 billion years

meters/second Mach Walk 1.5 Running sprint 10 Cycling sprint 20 Cheetah 30 Fastest land animal 70 miles/hour 31 Baseball pitch 45 100 miles/hour Human neuron 100 Sound at altitude 295 Speed of sound at altitude 10 km to 20 km 747 airplane 266 .9 Sound at sea level 340 1.0 At sea level and 15 degrees Celsius F-35 Lightning 475 1.6 Stealth fighter F-16 Falcon 590 2.0 Concorde 606 2.05 F-22 Raptor 670 2.3 Stealth fighter F-15 Eagle 740 2.5 SR-71 Blackbird 980 3.3 Orbit speed 7800 26.4 Minimum speed to orbit the Earth Escape speed 11200 38.0 Minimum speed to escape the Earth's gravity Ion rocket 100000 Fastest spacecraft we can build Fission rocket 10Aircraft typical fly at altitude 10 km to 20 km, where the speed of sound is 295 m/s. Mach 1 for aircraft is defined using this speed.^{7}Fusion rocket 10^{7}Light 3⋅10^{8}1020000

kg Earth Solar masses masses Electron 9.109⋅10^{-31}Proton 1.673⋅10^{-27}Neutron 1.675⋅10^{-27}1 ounce .0283 Tennis ball .058 Soccer ball .44 1 pound .454 Typical human 67 Sumo wrestler 230 Ton 1000 Honda Civic 1200 Elephant 5000 Bradley tank 27000 Argentinosaurus 70000 Largest dinosaur Blue whale 200000 Moon 7.35⋅10^{22}.0123 Mars 6.42⋅10^{23}.107 Earth 5.92⋅10^{24}1 Jupiter 1.90⋅10^{27}318 .00096 Sun 1.99⋅10^{30}330000 1.0 White dwarf max 2.9⋅10^{30}1.44 Milky Way black hole7.4⋅10^{36}4.2 million Milky Way 2.5⋅10^{42}1.2 trillion Andromeda 2.5⋅10^{42}1.2 trillion M87 galaxy 10 trillion Virgo galaxy cluster 1200 trillion

Ball sizes are magnified by 10 with respect to court sizes.

The distance from the back of the court to the ball is the characteristic distance the ball travels before losing half its speed to air drag.

Ball Ball Court Court Ball diameter Mass length width density (mm) (g) (m) (m) (g/cm^{3}) Ping pong 40 2.7 2.74 1.525 .081 Squash 40 24 9.75 6.4 .716 Golf 43 46 1.10 Badminton 54 5.1 13.4 5.18 .062 Racquetball 57 40 12.22 6.10 .413 Billiards 59 163 2.84 1.42 1.52 Tennis 67 58 23.77 8.23 .368 Baseball 74.5 146 .675 Pitcher-batter distance = 19.4 m Hockey puck 76 163 61 26 1.44 25 mm thick Whiffle 76 45 .196 Football 178 420 91.44 48.76 .142 Rugby 191 435 100 70 .119 Bowling 217 7260 18.29 1.05 1.36 Soccer 220 432 105 68 .078 Basketball 239 624 28 15 .087 Cannonball 220 14000 7.9 For an iron cannonball

grams/cm^{2}$/kg Year of discovery Magnesium 1.74 2.8 1808 Aluminum 2.70 1.7 1827 Titanium 4.51 10 1910 Zinc 7.14 2.0 1300 Manganese 7.21 2.3 1774 Iron 7.9 .3 -1200 Nickel 8.91 15 1751 Copper 8.96 6 -5000 Silver 10.49 640 Ancient Lead 11.3 2 -6500 Tungsten 19.25 50 1783 Gold 19.30 43000 Ancient Platinum 21.45 37000 1735 Osmium 22.59 12000 1803 Densest element Air at Everest .0004 10 km altitude Air at Denver .001 1 Mile altitude Air at sea level .00127 Ice .92 Water 1.0 Rock 2.8 Earth 5.52 Moon 3.35 Mars 3.95 Europa 3.10 Ganymede 1.94 Callisto 1.83 Titan 1.88 Balsa .12 Corkwood .21 Cedar .32 Pine .37 Spruce, red .41 Oak, red .66 Hickory .81 Bamboo .85 Oak, live .98 Ironwood 1.1 Lignum Vitae 1.26

Mass Diameter Height Density Price/kg Copper Nickel Zinc Manganese g mm mm g/cmThe above objects are all to scale. The dimensions of a dollar bill are 155.956 mm * 66.294 mm * .11 mm.^{3}$/kg fraction fraction fraction fraction Penny 2.5 19.05 1.52 5.77 4.0 .025 .975 Nickel 5.000 21.21 1.95 7.26 10.0 .75 .25 Dime 2.268 17.91 1.35 4.62 44.1 .9167 .0833 Quarter 5.670 24.26 1.75 6.29 44.1 .9167 .0833 Half dollar 11.340 30.61 2.15 7.90 44.1 .9167 .0833 Dollar 8.100 26.5 2.00 7.53 123.5 .885 .02 .06 .035 Dollar bill 1.0 .11 .88 1000

For a coin,

Mass = M Diameter = D Height = H Volume = Vol = π H DGold was the densest element known until the discovery of tungsten in 1783 and was hence valuable as an uncounterfeitable currency. Silver can be counterfeited with lead because lead is more dense and cheaper than silver.^{2}/ 4 Density = M / Vol

The price of the metal in a penny is

Metal price = Penny mass * (Copper fraction * Copper price/kg + Zinc fraction * Zinc price/kg) = .0025 kg * ( .025 6 $/kg .975 2 $/kg ) = .0052 $For a penny made of pure copper the price of the metal is 1.5 cents. A penny made of gold, silver, or zinc has a value of:

Price/Mass Price $/kg $ Zinc 2 .005 Copper 6 .015 Silver 640 1.6 Gold 43000 108

Frequency Note (Hertz) Whale songs 10 Human ear lower limit 20 Bass lowest note 41 E Bass guitar lowest note 41 E Cello lowest note 65 C Bass singer lowest note 82 E Viola & tenor lowest note 131 C Violin & alto lowest note 196 G Soprano lowest note 262 C Violin D string 293 D Violin A string 440 A Violin E string 660 E Human ear upper limit 20000

Kelvin Celsius Fahrenheit Absolute zero 0 -273.2 -459.7 Water melting point 273.2 0 32 Room temperature 294 21 70 Human body temperature 310 37 98.6 Water boiling point 373.2 100 212 Kelvin Absolute zero 0 Helium boiling point 4.2 Hydrogen boiling point 20.3 Triton 38 Pluto 44 Titania 70 Nitrogen boiling point 77.4 Oxygen boiling point 90.2 Titan 94 Europa 102 Hottest superconductor 135 HgBaCaCuO Ceres 168 Mars 210 Water melting point 273.15 Earth average 288 Room temperature 293 Water boiling point 373.15 Venus 740 Wood fire 1170 Copper melting point 1358 Iron melting point 1811 Bunsen burner 1830 Tungsten melting point 3683 Highest melting point among metals Earth's core 5650 Inner-core boundary Sun's surface 5780 Solar core 13.6 million Helium-4 fusion 200 million Carbon-12 fusion 230 million

Surface area = A Force = F Pressure = P = F / A (Pascals or Newtons/meter^{2}or Joules/meter^{3})

Mass of the Earth's atmosphere = M = 5.15e18 kg Surface area of the Earth = A = 5.10e14 mOne bar is defined as the Earth's mean atmospheric pressure at sea level^{2}Gravitational constant = g = 9.8 m/s^{2}Pressure on Earth's surface = P = M g / A = 101000 Pascals = 15 pounds/inch^{2}= 1 Bar

Height Pressure Density (km) (Bar) (kg/m^{3}) Sea level 0 1.00 1.225 Denver 1.6 .82 1.05 One mile Everest 8.8 .31 .48 Airbus A380 13.1 .16 .26 F-22 Raptor 19.8 .056 .091 SR-71 Blackbird 25.9 .022 .034 Space station 400 .000009 .000016

Energy = E Joules Time = T seconds Power = P = E/T Watts Mass = M kilograms Energy/Mass = e = E/M Joules/kilogram Power/Mass = p = P/M Watts/kilogram

Energies in MJoules = 10^{6} Joules

1 Watt hour .0036 1 Watt * 3600 seconds 1 food calorie .0042 Sprinting person .004 (80 kg moving at 10 m/s) Battery, lithium, AAA .0047 Battery, lithium, AA .0107 Battery, lithium, A .046 Battery, lithium, C .060 Battery, iPhone .018 ( 5 Watt hours) Battery, laptop .180 (50 Watt hours) 1 kg of Lithium battery 1.0 1 kg of TNT 4.2 1 kg of sugar 20 = 5000 Food Calories 1 kg of protein 20 = 5000 Food Calories 1 kg of alcohol 25 = 7000 Food Calories 1 kg of fat 38 = 9000 Food Calories 1 kg of gasoline 48 = 13000 Food Calories Uranium fission bomb (Little boy) 7⋅10Forms of energy:^{7}= 16 kilotons of TNT Plutonium fission bomb (Trinity) 8⋅10^{7}= 20 kilotons of TNT Uranium fission bomb (Fat man) 9⋅10^{7}= 22 kilotons of TNT Fusion bomb 4⋅10^{10}= 10 megatons of TNT World energy production in 1 year 6⋅10^{14}Energy Mass Velocity (Joule) (kg) (m/s) Ping pong ball 2.2 .0027 40 Squash ball 43 .024 60 Golf ball 230 .046 100 Tennis ball 104 .058 60 Baseball ball 116 .146 40 Soccer ball 778 .432 60 Bullet, 9 mm 338 .0065 323 Cannonball 1900000 14 518 220 mm diameter Human sprint 4000 80 10 Car, freeway 540000 1200 30

Distance = X meters Force = F Newtons Mass = M kg Velocity = V meters/second Gravity constant = g = 9.8 meters/second^{2}Pressure = P Pascals Volume = U meters^{3}Mechanical energy= E_{w}= F X Joules Gravity energy = E_{g}= MgX Joules (X = height above ground) Kinetic energy = E_{k}= ½MV^{2}Joules Pressure energy = E_{p}= P U Joules

Watts Human cell 10^{-12}Laptop computer 10 Human brain 20 Incandescent Light bulb 60 Human at rest 100 1 horsepower 746 Strenuous exercise 1000 Maximum human power 1600 World power per person 2500 Tesla S Ludicrous 397000 532 horsepower Wind turbine 1⋅10^{6}Blue whale 2.5⋅10^{6}Boeing 747 1.4⋅10^{8}Hoover Dam 2.1⋅10^{9}U.S. power consumption 3.4⋅10^{12}World power consumption 1.5⋅10^{13}Earth geologic heat 4.4⋅10^{13}World photosynthesis 7.5⋅10^{13}Earth solar power 1.7⋅10^{17}Total solar power falling on the Earth

Most fuels are combinations of carbon, hydrogen, and oxygen, and are collectively called "hydrocarbons".

Black: Carbon White: Hydrogen Red: Oxygen

The energy sources that can be used by vehicles are:

Energy/Mass Power/mass Energy/$ Rechargeable Charge Maximum charging MJoule/kg Watt/kg MJoule/$ time cycles Gasoline 45 60 Battery, aluminum 4.6 130 No Battery, lithium .8 1600 .010 Yes 1 hour 1000 Supercapacitor .016 8000 .00005 Yes Instant Infinite Aluminum capacitor .010 10000 .0001 Yes Instant Infinite

Energy/Mass Power/mass Density Energy/$ MJoule/kg Watt/kg MJoule/$ Antimatter 90000000000 Fusion bomb 250000000 Max for d+t fusion Fission bomb 83000000 Max for a uranium bomb Nuclear battery, Pu-238 2265000 10 7.6 88 year half life Nuclear battery, Sr-90 589000 10 59 29 year half life Hydrogen ( 0 carbons) 141.8 .07 Methane ( 1 carbon ) 55.5 .42 Natural gas Ethane ( 2 carbons) 51.9 .54 Propane ( 3 carbons) 50.4 .60 Butane ( 4 carbons) 49.5 .60 Octane ( 8 carbons) 47.8 .70 Kerosene (12 carbons) 46 .75 Diesel (16 carbons) 46 .77 Oil (36 carbons) 46 .8 Fat (20 carbons) 37 .9 1.0 9 Calories/gram Pure carbon 32.8 2.0 Coal 32 .8 Similar to pure carbon Ethanol ( 2 carbons) 29 .79 .2 7 Calories/gram Wood 22 .6 Sugar ( 6 carbons) 17 1.54 6 4 Calories/gram Protein 17 1.06 2 4 Calories/gram Plastic explosive 8.0 600000 1.91 HMX Smokeless powder 5.2 1.23 Modern gunpowder TNT 4.7 1.65 Black powder 2.6 1.7 Medieval gunpowder Phosphocreatine .137 Recharges ATP ATP .057 1.04 Adenosine triphosphate Battery, aluminum-air 4.68 130 Battery, Li-S 1.44 670 Battery, Li-ion .8 1600 .007 Battery, Li-polymer .6 4000 Battery, Alkaline .4 Battery, Lead acid .15 150 Lithium supercapacitor .054 15000 Supercapacitor .016 8000 .00005 Aluminum capacitor .010 10000 .0001 Spring .0003 Human 20 Solar cell, space station 77 Fuel cell 1000 Gasoline engine 8000 Electric motor 8000 Jet engine 10000 Rocket engine 3200000The energy cost to convert water to hydrogen and oxygen is 13.16 MJ/kg. If hydrogen and oxygen are reacted to produce one kg of water, the energy produced is equivalent to a 1 kg mass moving at 5.13 km/s.

Meters/second^{2}Ceres gravity .27 Europa gravity 1.31 Titan gravity 1.35 Moon gravity 1.62 Mars gravity 3.8 Venus gravity 8.87 Earth gravity 9.8 Bugatti Veyron 15.2 0 to 100 km/h in 2.4 seconds Red out 30 Max long-term acceleration in the direction of blood rushing to your head Blackout 50 Max long-term acceleration while sitting Formula-1 car 50 High-speed breaking and cornering with a downforce wing Blackout with g suit 90 Max long-term acceleration while sitting with a g-suit Max long-term (front) 120 Max long-term acceleration while lying on one's front Max long-term (back) 170 Max long-term acceleration while lying on one's back Max short-term 500 Max short-term acceleration Bullet 310000 9x19 Parabellum handgun, average acceleration along the barrel

Speed of light 2.9979e8 m/s Gravitational constant 6.6738e-11 m^{3}/kg/s^{2}Planck constant 6.6261e-34 J s Earth surface gravity 9.8067 m/s Electric force constant 8.9876e9 N m^{2}/ C^{2}Magnetic constant 4 Pi e-7 N/A^{2}Proton mass 1.6726e-27 kg = 938.272 GeV Neutron mass 1.6749e-27 kg = 939.565 GeV Electron mass 9.1094e-31 kg Electron charge 1.6022e-19 C Atomic mass unit 1.6605e-27 kg Bohr radius 5.2918e-11 m = hbar^{2}/ (ElectronMass*ElectronCharge^{2}*Ke) Boltzmann constant 1.3806e-23 J/K Avogadro number 6.0221e23 particles/mole Gas constant 8.3145 J/K/mole Stefan-Boltzmann constant 5.6704e-8 Watts/m^{2}/K^{4}Wein constant 2.8978e-3 m K Mole of Carbon-12 .012 kg Exact Planck length 1.6162e-35 m Planck mass 2.1765e-8 kg Planck time 5.3911e-44 s Planck charge 1.8755e-18 C Planck temperature 1.4168e32 K Water heat capacity 4200 J/kg/K Steam heat capacity 2080 J/kg/K At 100 Celsius Ice heat capacity 2110 J/kg/K At -10 Celsius Air heat capacity 1004 J/kg/K Stefan-Boltzmann 5.67e-8 Watts/meter^{2}/Kelvin^{4}= (2π^{5}/15) Boltzmann^{4}/ SpeedOfLight^{2}/ PlanckConstant^{3}Wein 2.898e-3 Kelvin meters Electron spin 5.2729e-35 Joule seconds = PlanckConstant / (4 Pi) Pi 3.14159 Euler number 2.71828

System Units Best suited for SI (MKS) Meters, Kilograms, Seconds Newtonian mechanics, EM forces between currents Gaussian (CGS) Centimeters, Grams, Seconds EM forces between particles, plasma physics, astrophysics Particle Meters, Electron Volts, Seconds Particle physics Planck Planck length, Planck mass, Planck time General relativity, quantum gravity 1 gram = .001 kg 1 cm = .01 meters 1 electron Volt (eV) = 1.602e-19 Joules = The energy gained by an electron upon descending a potential of 1 Volt

In this plot, the diameter of each particle proportional to CubeRoot(Mass). This is what the particles would look like if they were uniform-density spheres.

The electron is exaggerated otherwise it would be invisible.

The blue particles represent the heaviest particle that can be produced by each accelerator.

At this scale, a Big Bang particle has a diameter of 10 km.

Photons, Gluons, and Gravitons are massless.

Electron neutrino < 1 eV Muon neutrino < 2 eV Red photon 1.8 eV Green photon 2.3 eV Blue photon 3.1 eV Electron .51 MeV Up quark 1.9 MeV Down quark 4.4 MeV Strange quark 87 MeV Muon 105.7 MeV Neutral pion 135 MeV Charged pion 140 MeV Proton 938.27 MeV Neutron 939.57 MeV Charm quark 1.32 GeV Discovered at SLAC Tau 1.78 GeV Discovered at SLAC Bottom quark 4.24 GeV Discovered at Fermilab SLAC limit 45 GeV Highest-energy particle that SLAC can produce W boson 80 GeV Discovered at the Super Proton Synchrotron Z boson 91 GeV Discovered at the Super Proton Synchrotron Fermilab limti 125 GeV Highest-energy particle that Fermilab can produce Higgs Boson 125 GeV Discovered at the LHC Top quark 173 GeV Discovered at Fermilab LHC limit 1000 GeV Highest-energy particle that the LHC can produce Cosmic rays 10^12 GeV Highest-energy events observed Planck energy 10^19 GeV Quantum gravity. Planck energy = 1.22e28 eV = 1.956e9 Joules 1 electron Volt (eV) = 1.602e-19 Joules ~ kT at 11,000 Kelvin

Quantity MKS units CGS units Conversion factor_{}Mass M kg gram .001 Wire length Z meter cm .01 Radial distance from wire R meter cm .01 Time T second second 1 Force F Newton dyne 100000 Charge Q Coulomb Franklin 3.336e-10 Velocity of a charge V meter/second cm/s .01 Speed of light C 2.999e8 meter/second cm/s 100 Energy E Joule erg e-7 Electric currentAmpere = Coulomb/s Franklin/s 3.336e-10 Electric potentialIVolt Statvolt 299.79 Electric fieldVVolt/meter StatVolt/cm 29979 Magnetic fieldETesla Gauss 10000 CapacitanceBFarad cm 1.11e-12 InductanceCHenry sL^{2}/cm 9e-11 Electric force constant K_{e}= 8.988e9 N m^{2}/C^{2}K_{e}= 1 dyne cm^{2}/ Franklin^{2}Magnetic force constant K_{m}= 2e-7 = K_{e}/C^{2}K_{m}= 1/C^{2}Vacuum permittivity ε = 8.854e-12 F/m =1/4/π/K_{e}Vacuum permeability μ = 4 π e-7 Vs/A/m =2 π K_{m}Proton charge Q_{pro}= 1.602e-19 Coulomb Q_{pro}= 4.803e-10 Franklin Electric field from a charge= KE_{e}Q / R^{2}= Q / RE^{2}Electric force on a charge F = QF = QEElectric force between charges F = KE_{e}Q Q / R^{2}F = Q Q / R^{2}Magnetic field of moving charge= KB_{m}V Q / R^{2}= (V/C) Q / RB^{2}Magnetic field around a wire= KB_{m}/ RI= (V/C)B/ R Magnetic force on a charge F = Q VIF = (V/C) QBMagnetic force on a wire F = KB_{m}Z F =BIz Magnetic force between charges F = KB_{m}V^{2}Q_{1}Q_{2}/ R^{2}F = (V/C)^{2}Q Q / R^{2}Magnetic force between wires F = K_{m}I_{1}I_{2}Z / R F =I_{1}I_{2}Z / R Energy of a capacitor E = .5 C V^{2}Field energy per volume Z = (8 π K_{e})^{-1}(E^{2}+B^{2}/C^{2}) Z = .5 (E^{2}+B^{2}/C^{2})

Speed of light C Electric field E Electric field, time derivative E_{t}Magnetic field B Magnetic field, time derivative B_{t}Charge Q Charge density q Current density J MKS CGS K_{e}=8.988e9 K_{e}=1 K_{m}=2e-7 K_{m}=2/C ∇˙E = 4 π K_{e}q ∇˙E = 4 π q ∇˙B = 0 ∇˙B = 0 ∇×E = -B_{t}∇×E = -B_{t}/ C ∇×B = 2 π K_{m}J + E_{t}/ C^{2}∇×B = 4 π J / C + E_{t}/ C

Charges of the same sign repel and charges of opposite sign attract.

Charge 1 Charge 2 Electric Force + + Repel - - Repel + - Attract - + Attract Charge = Q (Coulombs) 1 Proton = 1.602e-19 Coulombs Distance between charges = R Mass of the charges = M Gravity constant = G = 6.67e-11 Newton m^{2}/ kg^{2}Electric constant = K = 8.99e9 Newton m^{2}/ Coulomb^{2}Gravity force = F = -G M_{1}M_{2}/ R^{2}= M_{2}g Electric force = F = -K Q_{1}Q_{2}/ R^{2}= Q_{2}E Gravity field from M_{1}= g = G M_{1}/ R^{2}Electric field from Q_{1}= E = K Q_{1}/ R^{2}Gravity voltage = H g (H = Height, g = Gravitational acceleration) Electric voltage = H E (H = Distance parallel to the electric field) Gravity energy = -G M_{1}M_{2}/ R Electric energy = -K Q_{1}Q_{2}/ R

A charge generates an electric field. The electric field points away from positive charges and toward negative charges.

A moving charge is an "electric current". In an electric circuit, a battery moves electrons through a wire.

Charge = Q Time = T Electric current =The current from a positive charge moving to the right is equivalent to that from a negative charge moving to the left.= Q / T (Coulombs/second)I

Moving charges and currents exert forces on each other. Parallel currents attract and antiparallel currents repel.

Charge = Q Velocity of the charges = V Current = I Length of a wire = L Distance between the charges = R Electric force constant = KThe magnetic force is always less than the electric force._{e}= 8.988e9 N m^{2}/C^{2}Magnetic force constant = K_{m}= 2e-7 = K_{e}/C^{2}Electric force between charges = F_{e}= K_{e}Q_{1}Q_{2}/ R^{2}Magnetic force between charges = F_{m}= K_{m}V^{2}Q_{1}Q_{2}/ R^{2}= (V^{2}/C^{2}) F_{e}Magnetic force between currents = F_{m}= K_{m}I_{1}I_{2}Z / R Magnetic force / Electric force = V^{2}/ C^{2}

The electric force can be interpreted as an electric field, and the magnetic force can be interpreted as a magnetic field. Both interpretations produce the same force.

Radial distance = R (Distance perpendicular to the velocity of the charge) Magnetic field from charge Q_{1}== KB_{m}V Q_{1}/ R^{2}Magnetic field from currentI_{1}== KB_{m}I_{1}/ R Magnetic force on charge Q_{2}= F_{m}= Q_{2}V= KB_{m}V^{2}Q_{1}Q_{2}/ R^{2}Magnetic force on currentI_{2}= F_{m}=I_{2}Z= KB_{m}I_{1}I_{2}Z / R

The direction of the magnetic force on a positive charge is given by the right hand rule. The force on a negative charge is in the opposite direction (the left hand rule).

We use the above symbols to depict vectors in the Z direction. The vector on the left points into the plane and the vector on the right points out of the plane.

The direction of the force is the cross product "×" of V and B. The direction is given by the "right hand rule".

Magnetic field = B Magnetic force on a charge = F = Q V × B Magnetic force on a current = F = 2e-7 I × B

Voltage = V Volts Capacitance = C Farads Total energy = E = ½ C VNot all of the energy in a capacitor is harnessable because the voltage diminishes as the charge diminishes, hence the effective energy is less than the total energy.^{2}Joules Effective = E_{e}= ¼ C V^{2}Joules

White: High conductivity Red: Low conductivity

Electric Thermal Density Electric C/Ct Heat Heat Melt $/kg Young Tensile Poisson Brinell conduct conduct conduct/ cap cap number hardness (e7 A/V/m) (W/K/m) (g/cm^3) Density (AK/VW) (J/g/K) (J/cm^3K) (K) (GPa) (GPa) (GPa) Silver 6.30 429 10.49 .60 147 .235 2.47 1235 590 83 .17 .37 .024 Copper 5.96 401 8.96 .67 147 .385 3.21 1358 6 130 .21 .34 .87 Gold 4.52 318 19.30 .234 142 .129 2.49 1337 24000 78 .124 .44 .24 Aluminum 3.50 237 2.70 1.30 148 .897 2.42 933 2 70 .05 .35 .245 Beryllium 2.5 200 1.85 1.35 125 1.825 3.38 1560 850 287 .448 .032 .6 Magnesium 2.3 156 1.74 1.32 147 1.023 1.78 923 3 45 .22 .29 .26 Iridium 2.12 147 22.56 .094 144 .131 2.96 2917 13000 528 1.32 .26 1.67 Rhodium 2.0 150 12.41 .161 133 .243 3.02 2237 13000 275 .95 .26 1.1 Tungsten 1.89 173 19.25 .098 137 .132 2.54 3695 50 441 1.51 .28 2.57 Molybdenum 1.87 138 10.28 .182 136 .251 2896 24 330 .55 .31 1.5 Cobalt 1.7 100 8.90 .170 .421 1768 30 209 .76 .31 .7 Zinc 1.69 116 7.14 .388 693 2 108 .2 .25 .41 Nickel 1.4 90.9 8.91 .444 1728 15 Ruthenium 1.25 117 12.45 2607 5600 Cadmium 1.25 96.6 8.65 594 2 50 .078 .30 .20 Osmium 1.23 87.6 22.59 .130 3306 12000 Indium 1.19 81.8 7.31 430 750 11 .004 .45 .009 Iron 1.0 80.4 7.87 .449 1811 211 .35 .29 .49 Palladium .95 71.8 1828 Tin .83 66.8 505 22 47 .20 .36 .005 Chromium .79 93.9 .449 2180 Platinum .95 .133 2041 Tantalum .76 .140 3290 Gallium .74 303 Thorium .68 Niobium .55 53.7 2750 Rhenium .52 .137 3459 Vanadium .5 30.7 2183 Uranium .35 Titanium .25 21.9 .523 1941 Scandium .18 15.8 1814 Neodymium .156 1297 Mercury .10 8.30 .140 234 Manganese .062 7.81 1519 Germanium .00019 1211 Dimond iso 10 40000 Diamond e-16 2320 .509 Tube 10 3500 Carbon nanotube. Electric conductivity = e-16 laterally Tube bulk 200 Carbon nanotubes in bulk Graphene 10 5000 Graphite 2 400 .709 Natural graphite Al Nitride e-11 180 Brass 1.5 120 Steel 45 Carbon steel Bronze .65 40 Steel Cr .15 20 Stainless steel (usually 10% chromium) Quartz (C) 12 Crystalline quartz. Thermal conductivity is anisotropic Quartz (F) e-16 2 Fused quartz Granite 2.5 Marble 2.2 Ice 2 Concrete 1.5 Limestone 1.3 Soil 1 Glass e-12 .85 Water e-4 .6 Seawater 1 .6 Brick .5 Plastic .5 Wood .2 Wood (dry) .1 Plexiglass e-14 .18 Rubber e-13 .16 Snow .15 Paper .05 Plastic foam .03 Air 5e-15 .025 Nitrogen .025 1.04 Oxygen .025 .92 Silica aerogel .01 Siemens: Amperes^2 Seconds^3 / kg / meters^2 = 1 Ohm^-1For most metals,

Electric conductivity / Thermal conductivity ~ 140 J/g/K

Teslas Field generated by brain 10^{-12}Wire carrying 1 Amp .00002 1 cm from the wire Earth magnetic field .0000305 at the equator Neodymium magnet 1.4 Magnetic resonance imaging machine 8 Large Hadron Collider magnets 8.3 Field for frog levitation 16 Strongest electromagnet 32.2 without using superconductors Strongest electromagnet 45 using superconductors Neutron star 10^{10}Magnetar neutron star 10^{14}

The critical electric field for electric breakdown for the following materials is:

MVolt/meter Air 3 Glass 12 Polystyrene 20 Rubber 20 Distilled water 68 Vacuum 30 Depends on electrode shape Diamond 2000

Relative permittivity is the factor by which the electric field between charges is decreased relative to vacuum. Relative permittivity is dimensionless. Large permittivity is desirable for capacitors.

Relative permittivity Vacuum 1 (Exact) Air 1.00059 Polyethylene 2.5 Sapphire 10 Concrete 4.5 Glass ~ 6 Rubber 7 Diamond ~ 8 Graphite ~12 Silicon 11.7 Water (0 C) 88 Water (20 C) 80 Water (100 C) 55 TiO2 ~ 150 SrTiO3 310 BaSrTiO3 500 Ba TiO3 ~ 5000 CaCuTiO3 250000

A ferromagnetic material amplifies a magnetic field by a factor called the "relative permeability".

Relative Magnetic Maximum Critical permeability moment frequency temperature (kHz) (K) Metglas 2714A 1000000 100 Rapidly-cooled metal Iron 200000 2.2 1043 Iron + nickel 100000 Mu-metal or permalloy Cobalt + iron 18000 Nickel 600 .606 627 Cobalt 250 1.72 1388 Carbon steel 100 Neodymium magnet 1.05 Manganese 1.001 Air 1.000 Superconductor 0 Dysprosium 10.2 88 Gadolinium 7.63 292 EuO 6.8 69 Y3Fe5O12 5.0 560 MnBi 3.52 630 MnAs 3.4 318 NiO + Fe 2.4 858 CrO2 2.03 386

Resistivity in 10^-9 Ohm Meters

293 K 300 K 500 K Beryllium 35.6 37.6 99 Magnesium 43.9 45.1 78.6 Aluminum 26.5 27.33 49.9 Copper 16.78 17.25 30.9 Silver 15.87 16.29 28.7

Electric quantities | Thermal quantities | Q = Charge Coulomb | Etherm= Thermal energy Joule I = Current Amperes | Itherm= Thermal current Watts E = Electric field Volts/meter | Etherm= Thermal field Kelvins/meter C = Electric conductivity Amperes/Volt/meter | Ctherm= Thermal conductivity Watts/meter/Kelvin A = Area meter^2 | A = Area meter^2 Z = Distance meter | Z = Distance meter^2 J = Current flux Amperes/meter^2 | Jtherm= Thermal flux Watts/meter^2 = I / A | = Ittherm / A = C * E | = Ctherm * Etherm V = Voltage Volts | Temp = Temperature difference Kelvin = E Z | = Etherm Z = I R | = Itherm Rtherm R = Resistance Volts/Ampere = Ohms | Rtherm= Thermal resistance Kelvins/Watt = Z / (A C) | = Z / (A Ct) H = Current heating Watts/meter^3 | = E J | P = Current heating power Watts | = E J Z A | = V I |

L = Length of wire meters A = Cross section of wire meters^2 _______________________________________________________________________________________________________ | Electric quantities | Thermal quantities | Q = Charge Coulomb | Etherm= Thermal energy Joule I = Current Amperes | Itherm= Thermal current Watts E = Electric field Volts/meter | Etherm= Thermal field Kelvins/meter C = Electric conductivity Amperes/Volt/meter | Ctherm= Thermal conductivity Watts/meter/Kelvin A = Area meter^2 | A = Area meter^2 Z = Distance meter | Z = Distance meter^2 J = Current flux Amperes/meter^2 | Jtherm= Thermal flux Watts/meter^2 = I / A | = Ittherm / A = C * E | = Ctherm * Etherm V = Voltage Volts | Temp = Temperature difference Kelvin = E Z | = Etherm Z = I R | = Itherm Rtherm R = Resistance Volts/Ampere = Ohms | Rtherm= Thermal resistance Kelvins/Watt = Z / (A C) | = Z / (A Ct) H = Current heating Watts/meter^3 | = E J | P = Current heating power Watts | = E J Z A | = V I |

Continuum quantity Macroscopic quantity E <-> V C <-> R = L / (A C) J = C E <-> I = V / R H = E J <-> P = V I

Viscosity is analogous to electrical conductivity and thermal conductivity.

Quantity Electricity Thermal Viscosity Stuff Coulomb Joule Momentum Stuff/volume Coulomb/m^3 Joule/m^3 Momentum/m^3 Flow = Stuff/time Coulomb/second Joule/s Momentum/s Potential Volts Kelvin Momentum/m^3 Field Volts/meter Kelvins/meter Momentum/m^3/m Flow density = Flow/m^2 Amperes/meter^2 Watts/meter^2 Momentum/s/m^2 Conductivity Amperes/Volt/meter Watts/meter/Kelvin m^2/s Resistance Volts/Ampere Kelvins/Watt s/m^3 Flow density = Conductivity * Field Flow = Potential / Resistance Field = -Gradient(Potential)

Fluid density = ρ (kg/meter^{3}) Fluid velocity = V Fluid momentum density = U = D V Kinematic viscosity = ν_{k}(meters^{2}/ second) Dynamic viscosity = ν_{d}= ρ ν_{k}(Pascal seconds) Lagrangian time deriv. = D_{t}D_{t}U = ∇⋅(ν_{d}∇U) D_{t}V = ∇⋅(ν_{k}∇V)

Dynamic Kinematic Density viscosity viscosity (kg/m1 Stokes = 1 cm^{3}) (Pa s) (m^{2}/s) Hydrogen .00000876 Nitrogen .0000178 Air .0000183 .0000150 1.22 Helium .000019 Oxygen .0000202 Xenon .0000212 Acetone .00031 Benzine .00061 Water at 2 C .00167 Water at 10 C .00131 .0000010 1000 Water at 20 C .00100 1000 Water at 30 C .000798 1000 Water at 100 C .000282 1000 Mercury .00153 .00000012 Blood .0035 Motor oil .065 Olive oil .081 Honey 6 Peanut butter 250 Asthenosphere 7e19 Weak layer between the curst and mantle Upper mantle .8e21 Lower mantle 1.5e21

Schmidt number = Momentum diffusivity / Mass diffusivity Prandtl number = Momentum diffusivity / Thermal diffusivity Magnetic Prandtl number = Momentum diffusivity / Magnetic diffusivity Prandtl Schmidt Air .7 .7 Water 7 Liquid metals << 1 Oils >> 1

Critical Critical Type temperature field (Kelvin) (Teslas) Magnesium-Boron2 39 55 2 MRI machines Niobium3-Germanium 23.2 37 2 Field for thin films. Not widely used Magnesium-Boron2-C 34 36 Doped with 5% carbon Niobium3-Tin 18.3 30 2 High-performance magnets. Brittle Vanadium3-Gallium 14.2 19 2 Niobium-Titanium 10 15 2 Cheaper than Niobium3-Tin. Ductile Niobium3-Aluminum Technetium 11.2 2 Niobium 9.26 .82 2 Vanadium 5.03 1 2 Tantalum 4.48 .09 1 Lead 7.19 .08 1 Lanthanum 6.3 1 Mercury 4.15 .04 1 Tungsten 4 1 Not BCS Tin 3.72 .03 1 Indium 3.4 .028 Rhenium 2.4 .03 1 Thallium 2.4 .018 Thallium 2.39 .02 1 Aluminum 1.2 .01 1 Gallium 1.1 Gadolinium 1.1 Protactinium 1.4 Thorium 1.4 Thallium 2.4 Molybdenum .92 Zinc .85 .0054 Osmium .7 Zirconium .55 Cadmium .52 .0028 Ruthenium .5 Titanium .4 .0056 Iridium .1 Lutetium .1 Hafnium .1 Uranium .2 Beryllium .026 Tungsten .015 HgBa2Ca2Cu3O8 134 2 HgBa2Ca Cu2O6 128 2 YBa2Cu3O7 92 2 C60Cs2Rb 33 2 C60Rb 28 2 2 C60K3 19.8 .013 2 C6Ca 11.5 .95 2 Not BCS Diamond:B 11.4 4 2 Diamond doped with boron In2O3 3.3 3 2The critical fields for Niobium-Titanium, Niobium3-Tin, and Vanadium3-Gallium are for 4.2 Kelvin.

All superconductors are described by the BCS theory unless stated otherwise.

Boiling point (Kelvin) Water 273 Ammonia 248 Freon R12 243 Freon R22 231 Propane 230 Acetylene 189 Ethane 185 Xenon 165.1 Krypton 119.7 Oxygen 90.2 Argon 87.3 Nitrogen 77.4 Threshold for cheap superconductivity Neon 27.1 Hydrogen 20.3 Cheap MRI machines Helium-4 4.23 High-performance magnets Helium-3 3.19The record for Niobium3-Tin is 2643 Amps/mm^2 at 12 T and 4.2 K.

Titan has a temperature of 94 Kelvin, allowing for superconducting equipment. The temperature of Mars is too high at 210 Kelvin.

The maximum current density decreases with temperature and magentic field.

Maximum current density in kAmps/mm^{2} for 4.2 Kelvin (liquid helium):

Teslas 16 12 8 4 2 Niobium3-Tin 1.05 3 Niobium3-Aluminum .6 1.7 Niobium-Titanium - 1.0 2.4 3 Magnesium-Boron2-C .06 .6 2.5 4 Magnesium-Boron2 .007 .1 1.5 3Maximum current density in Amps/mm

Teslas 4 2 Magnesium-Boron2-C .4 1.5 Magnesium-Boron2 .12 1.5

1898 Dewar liquefies hydrogen (20 Kelvin) using regenerative cooling and his invention, the vacuum flask, which is now known as a "Dewar". 1908 Helium liquified by Onnes. His device reached a temperature of 1.5 K 1911 Superconductivity discovered by Onnes. Mercury was the first superconductor found 1935 Type 2 superconductivity discovered by Shubnikov 1953 Vanadium3-Silicon found to be superconducting, the first example of a superconducting alloy with a 3:1 chemical ratio. More were soon found 1954 Niobium3-Tin superconductivity discovered 1955 Yntema builds the first superconducting magnet using niobium wire, reaching a field of .7 T at 4.2 K 1961 Niobium3-Tin found to be able to support a high current density and magnetic field (Berlincourt & Hake). This was the first material capable of producing a high-field superconducting magnet and paved the way for MRIs. 1962 Niobium-Titanium found to be able to support a high current density and magnetic field. (Berlincourt & Hake) 1965 Superconducting material found that could support a large current density (1000 Amps/mm^2 at 8.8 Tesla) (Kunzler, Buehler, Hsu, and Wernick) 1986 Superconductor with a high critical temperature discovered in a ceramic (35 K) (Lanthanum Barium Copper Oxide) (Bednorz & Muller). More ceramics are soon found to be superconducting at even higher temperatures. 1987 Nobel prize awarded to Bednorz & Muller, one year after the discovery of high-temperature superconductivity. Nobel prizes are rarely this fast.

n = Electron density M = Electron mass V = Electron thermal velocity Q = Proton charge k = Boltzmann constant Temp = Temperature Xdebye = Debye length (k*Temp/n/Q^2/(4 Pi Ke))^.5 Xgyro = Electron gyro radius M V / Q B Fgyro = Electron gyrofrequency Electron Temp Debye Magnetic density (K) (m) field (T) (m^-3) Solar core e32 e7 e-11 - ITER 1.0e20 e8 e-4 5.3 Laser fusion 6.0e32 e8 - National Ignition Facility. density=1000 g/cm^3 Gas discharge e16 e4 e-4 - Ionosphere e12 e3 e-3 e-5 Magnetosphere e7 e7 e2 e-8 Solar wind e6 e5 e1 e-9 Interstellar e5 e4 e1 e-10 Intergalactic e0 e6 e5 - ITER ion temperature = 8.0 keV ITER electron temperature = 8.8 keV ITER confinement time = 400 seconds

Compression Heating Fusion Heating Density Year laser (MJ) laser (MJ) energy time (kg/m^3) (MJ) (s) NOVA .3 1984. LLNL National Ignition Facility (NIF) 330 - 20 .9 2010 HiPER .2 .07 30 e-11 .3 Future

terameter = Tm = 10$12$ meters gigameter = Bm = 10$9$ meters megameter = Mm = 10$6$ meters kilometer = km = 10$3$ meters meter = m = 10$0$ meters centimeter = cm = 10$-2$ meters millimeter = mm = 10$-3$ meters micrometer = μm = 10$-6$ meters nanometer = nm = 10$-9$ meters picometer = pm = 10$-12$ meters femtometer = fm = 10$-15$ meters 1 million kg = 1 Mkg 1 million dollars = 1 M$

Examples of scientific notation.

1 = 10The abbreviation "e" for "10^" comes from Fortran and is standard in all programming languages.^{0}= e0 10 = 10^{1}= e1 100 = 10^{2}= e2 123 = 1.23⋅10^{2}= 1.23e2 .123 = 1.23⋅10^{-1}= 1.23e-1 11000 * .012 = 1.1⋅10^{4}* 1.2⋅10^{-2}= 1.32⋅10^{2}= 132

A measurement consists of a quantity and an estimated error. For example, you might measure the length of a room to be

Length = 6.35 ± .02 meters"6.35" is the measurement and ".02" is the estimated error.

Care should be taken to use an appropriate number of digits. For example,

Length = 6.3 ± .02 meters Not enough digits in the measured quantity Length = 6.34 ± .02 meters Minimum number of digits to state the measured quantity Length = 6.342 ± .02 meters It is wise to to include an extra digit Length = 6.3421 ± .02 meters Too many digits. The last digit is unnecessary.The fractional error is defined as

Fractional error = Error / Measured quanitity = .02 / 6.34 = .0032Rounding:

6.3424 → 6.342 6.3425 → 6.342 6.3426 → 6.343If the last digit is even then round down, and if odd then round up. This prevents bias in rounding. For example:

6.05 → 6.0 6.15 → 6.2 6.25 → 6.2 6.35 → 6.4 6.45 → 6.4 6.55 → 6.6 6.65 → 6.6 6.75 → 6.8 6.85 → 6.8 6.95 → 7.0

1 mile = 1609 meters 1 hour = 3600 seconds 1609 meters 1 hour 1 mile/hour = 1 mile/hour * ----------- * ------------ = .447 meters/second 1 mile 3600 seconds

If you have data that is not in SI units, then the safest procedure is to convert everything to SI units do the calculation. You can't go wrong with this. For example, if a car moving at 70 mph travels for 2 hours, how far does it go?

Speed of a car = V = 70 mph = 31.3 meters/second Time traveled = T = 2 hours = 7200 seconds Distance traveled = X = V T = 140 miles = 225360 metersOne first converts 70 mph and 2 hours to SI units, then apply X=VT to arrive at X=225360 meters, and then convert this to mph.

Alternatively, you can do the calculation in non-SI units but care must be taken to make sure the units are consistent.

The logarithm is the inverse of the exponential function.

10^{-2}= .01 log_{10}.01 = -2 10^{-1}= .1 log_{10}.1 = -1 10^{0}= 1 log_{10}1 = 0 10^{1}= 10 log_{10}10 = 1 10^{2}=100 log_{10}100 = 2 10^{log10x}= log_{10}10^{x}= x

Many phenomena are besty understood by constructing a 2D table of numbers. For example, suppose you're wondering how to compare the alcohol content of a 6 pack of beer, a bottle of wine, and a bottle of Scotch. The following section constructs a table to show the alcohol content.

A typical bottle of beer has a volume of 12 ounces, is 5% alcohol, and contains

.6 ounces of alcohol. We use this amount as a reference unit and define

.6 ounces of alcohol to be one "Bond".

Volume of the drink = V Fraction of alcohol = F Volume of alcohol = V_{alc}= F V Volume of one beer = V_{beer}= 12 ounces Alcohol fraction of beer = F_{beer}= .05 Alcohol volume in one beer = V_{Bond}= .6 ounces One "Bond" of alcohol = .6 ounces One wine or Scotch bottle = 25.4 ounces = 750 ml One ounce = 29.6 mL Alcohol Volume Alcohol Alcohol $ $/Bond fraction (oz) (oz) (Bonds) Beer (12 oz) .05 12 .6 1 .67 .67 Budweiser Wine glass .13 4.6 .6 1 8 8.0 Napa Valley Scotch shot .40 1.5 .6 1 8 8.0 Laphroaig Beer pitcher .05 64 3.2 5.3 16 3.0 Budweiser Beer keg .05 1984 99.2 165.3 100 .60 Budweiser Wine bottle .13 25.4 3.3 5.5 3 .55 Charles Shaw Vodka bottle .40 25.4 10.1 16.9 15 .89 Smirnoff Scotch bottle .40 25.4 10.1 16.9 50 3.0 Laphroaig Distilled ethanol .95 25.4 24.1 40.2 15 .37 Everclear

Order of magnitude physics is a style for generating numerical estimates with a minimum of calculation, and using units arguments to obtain formulae.

Equations can often be derived using units. For example, what is the formula for kinetic energy? The variables that will be present in the formula are:

Mass = M (kg) Velocity = V (meters/second) Kinetic energy = E (Joules = kg metersAssume the formula as the form^{2}/second^{2}) Dimensionless constant = K (Unitless)

E = K MFor some value of m and v. The values that gives units of energy are:^{m}V^{v}

E = K MUnits arguments often give the right formula up to a dimensionless constant and a more involved derivation is usually required to produce the constant. The formula with the dimensionless constant included can always be found on Wikipedia. For the kinetic energy, K=½ and E = ½ M V^{1}V^{2}

Another example of using units to derive formulae is the aerodynamic drag force. The variables that will be present in the formula are:

Velocity = V meters/second Cross sectional area = A metersAssume the formula has the form^{2}Density of air = D = 1.22 kg/meter^{3}Drag force = F Newtons = kg meters/second^{2}Dimensionless constant= K Unitless

F = K Dfor some value of {d,a,v}. The values that give units of force are^{d}A^{a}V^{v}

F = K D^{1}A^{1}V^{2}

Aerodynamic drag force = 1/2 Density CrossSection Velocity^{2}Aerodynamic drag power = 1/2 Density CrossSection Velocity^{3}Gravitational force = -G Mass_{1}Mass_{2}/ Distance^{2}Gravitational energy = -G Mass_{1}Mass_{2}/ Distance Gravitational self-energy = 3/5 G Mass^{2}/ Radius For a sphere of uniform density Kinetic energy = 1/2 Mass Velocity^{2}Sound Speed = [Γ Pressure / Density]^{1/2}Γ=7/5 for air Wave speed for a string = [Tension Length / Mass]^{1/2}

© Jason Maron, all rights reserved.