Water Rocket Computer Model Help      
Rocket Environment

Unless you are seeing what it would be like to launch on a
different planet or use a different liquid or gas, you wouldn't
normally need to change any of the parameters in this box.

However...

  • Gamma: the compresibility of a gas depends upon
    its molecules - whether the gas is made from single
    atoms, for example with the noble gasses, He, Ne,
    Ar etc or diatomic molecules such as O2, N2, Cl2 or
    more complex molecules such as CH4, CO2, C2H6,
    C3H6, C3H8 and so on.

    The value is the ratio of heat capacities at constant
    volume and constant pressure and is in effect how
    springy it is.

    Example values are:

    • Air = 1.402;
    • Ar = 1.662;
    • He = 1.66;
    • C2H6 = 1.26; and,
    • CO2 = 1.304.
  • Gas Density: the amount of gas in a given volume.
    Counter-intuitively, a particular volume will contain
    the same number of gas molecules regardless of
    what that gas is. In this way, we can work out
    density of a gas from its molecular weight (or
    atomic weight in the case of a monatomic gas).

    The magic volume is 22.4litres which contains
    one mole of gas. Another way of looking at it is
    that a cubic metre of gas at STP holds a little
    over 44.6 moles of gas so if you were going to use
    Xenon (cost is not an issue here...) - its atomic
    weight is 131.29 and it is a noble gas so its density
    would be 44.6 x131.29 = 5,956gm-3 or 5.956kgm-3.

    Example values are:

    • Air = 1.293;
    • Ar = 1.784;
    • He = 0.179;
    • C2H4 = 1.260; and,
    • CO2 = 1.977.
  • Liquid Density: This is the density of the liquid at
    the ambient temperature.

    Example values are:

    • Water = 998;
    • Seawater = 1025;
    • Hg = 13546;
    • Olive Oil = 920,
    • CCl4 = 1632; and,
    • Br = 3100.
  • Acceleration due to gravity: If you are thinking
    about how this rocket would perform on the Moon,
    Mars or some exoplanet, put the value in here.

    Example values are:

    • Sun = 274;
    • Moon = 1.62;
    • Mercury = 3.76;
    • Venus = 8.77;
    • Earth = 9.81;
    • Mars = 3.80;
    • Jupiter = 24.9;
    • Saturn = 10.4;
    • Uranus = 10.4;
    • Neptune = 13.8; and,
    • Pluto = 4.0.
  • Atmospheric Pressure: Insert the barometric
    pressure here. Note that this is the barometric
    pressure where you are launching from and not
    necessarily the pressure at lea level. If you are
    launching at high altitude, this can become
    relevant because it affects drag force on the
    rocket of the atmospheric air of its surroundings.
  • Density of Atmospheric Gas

    Example values are:

    • Air = 1.293;
    • NH3 = 0.771;
    • He = 0.179;
    • H2 = 0.090;
    • CH4 = 0.717;
    • SO2 = 2.927; and,
    • CO2 = 1.977.
    Note that if the air pressure is substantially lower
    or higher than that on Earth, still put the value at
    STP into the density but put the atmospheric
    pressure in the box above.