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This is why atomic hydrogen escapes preferentially from an atmosphere. If there is a strong thermally driven atmospheric escape of light atoms, heavier atoms can achieve the escape velocity through viscous drag by those escaping lighter atoms. [2] This is another way of thermal escape, called hydrodynamic escape.
One classical thermal escape mechanism is Jeans escape, [1] named after British astronomer Sir James Jeans, who first described this process of atmospheric loss. [2] In a quantity of gas, the average velocity of any one molecule is measured by the gas's temperature, but the velocities of individual molecules change as they collide with one another, gaining and losing kinetic energy.
An alternative expression for the escape velocity v e particularly useful at the surface on the body is: = where r is the distance between the center of the body and the point at which escape velocity is being calculated and g is the gravitational acceleration at that distance (i.e., the surface gravity). [11]
Thus, if the molecular weight of one gas is four times that of another, it would diffuse through a porous plug or escape through a small pinhole in a vessel at half the rate of the other (heavier gases diffuse more slowly). A complete theoretical explanation of Graham's law was provided years later by the kinetic theory of gases.
Newton's cannonball was a thought experiment Isaac Newton used to hypothesize that the force of gravity was universal, and it was the key force for planetary motion. It appeared in his posthumously published 1728 work De mundi systemate (also published in English as A Treatise of the System of the World ).
In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. [1] Such a hole is often described as a pinhole and the escape of the gas is due to the pressure difference between the container and the exterior.
Chemical kinetics experiments can then be carried out in a pump–probe fashion, using a laser to initiate the reaction (for example, by preparing one of the reagents by photolysis of a precursor), followed by observation of that same species (for example, by laser-induced fluorescence) after a known time delay.
In astrodynamics, the characteristic energy is a measure of the excess specific energy over that required to just barely escape from a massive body. The units are length 2 time −2, i.e. velocity squared, or energy per mass.