Values for Backs of Envelopes
- Page ID
- 24451
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| \(\pi\) | pi | 3 |
| G | Newton's constant | \(7 \times 10^{-1} kh^{-1} m^{3} s^{-2}\) |
| c | speed of light | \(3 \times 10^{8} m s^{-1}\) |
| hc | h shortcut | 200 eV nm |
| \(m_{3}c^{2}\) | electron rest energy | 0.5 MeV |
| \(k_{B}\) | Boltzmann's constant | \(10^{-4} eV K^{1}\) |
| \(N_{A}\) | Avogadro's number | \(6 \times 10^{23} mol^{-1}\) |
| R | universal gas constant \(k_{B}N_{A}\) | \(8 J mol^{-1} K^{-1}\) |
| e | electron charge | \(1.6 \times 10^{-19} C\) |
| \(\frac{e^{2}}{4 \pi \epsilon _{0}}\) | electrostatic combination | \(2.3 \times 10^{-28} kg m^{3} s^{-2}\) |
| \(\frac{e^{2}}{4 \pi \epsilon_{0}} /hc\) | fine-structure constant \(\alpha\) | \(0.7 \times 10^{-2}\) |
| \(\sigma\) | Stefan-Boltzmann constant | \(6 \times 10^{-8} W m^{-2} K^{-4}\) |
| \(M_{Sun}\) | solar mass | \(2 \times 10^{30} kg\) |
| \(m_{Earth}\) | Earth's mass | \(6 \times 10^{24} kg\) |
| \(R_{Earth}\) | Earth's radius | \(6 \times 10^{6} m\) |
| AU | Earth-Sun distance | \(1.5 \times 10^{11} m\) |
| \(\Theta _{Moon or Sun}\) | angular diameter of Moon or Sun | \(10^{-2} rad\) |
| day | length of a day | \(10^{5} s\) |
| year | length of a year | \(\pi \times 10^{7} s\) |
| \(t_{0}\) | age of the universe | \(1.4 \times 10^{10} yr\) |
| F | solar constant | \(1.3 kW m^{-2}\) |
| \(p_{0}\) | atmospheric pressure at sea level | \(10^{5} Pa\) |
| \(\rho _{air}\) | air density | \(1 kg m^{-3}\) |
| \(\rho _{rock}\) | rock density | \(2.5 g cm^{-3}\) |
| \(L_{vap}^{water}\) | heat of vaporization of water | \(2 MJ kg^{-1}\) |
| \(\gamma_{water}\) | surface tension of water | \(7 \times 10^{-2} N m^{-1}\) |
| \(P_{basal}\) | human basal metabolic rate | \(100 W\) |
| \(a_{0}\) | Bohr radius | 0.5 Å |
| a | typical interatomic spacing | 3 Å |
| \(E_{bond}\) | typical bond energy | 4 eV |
| \(\varepsilon_{fat}\) | combustion energy density | \(9 kcal g^{-1}\) |
| \(v_{air}\) | kinematic viscosity of air | \(1.5 \times 10^{-5} m^{2} s^{-1}\) |
| \(v_{water}\) | kinematic viscosity of water | \(10^{-6} m^{2} s^{-1}\) |
| \(K_{air}\) |
thermal conduvtivity of air |
\(2 \times 10^{-2} W m^{-1} K^{-1}\) |
| K | ...of nonmetallic solids/liquids | \(2 W m^{-1} K^{-1}\) |
| \(K_{metal}\) | ...of metals | \(2 \times 10^{2} W m^{-1} K^{-1}\) |
| \(c_{p}^{air}\) | specific heat of air | \(1 J g^{-1} K^{-1}\) |
| \(c_{p}\) | ...of solids/liquids | \(25 J mol^{-1} K^{-1}\) |