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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 \(25 J mol^{-1} K^{-1}\)
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