Frequency of exceedance any peak exceeding is . Its complement, is the probability of exceedance, the probability that has been exceeded at least once by time . This probability can be useful to estimate whether an extreme event will occur during a specified time period, such as the lifespan of a structure or the duration of an operation. If is small, for example for the frequency of a rare event occurring in a short time period, then Under this assumption, the frequency of exceedance is equal to the probability of exceedance per unit time, , and the probability of exceedance can be computed
Kinetic theory of gases can calculate the number of atomic or molecular collisions with a wall of a container per unit area per unit time. Assuming an ideal gas, a derivation results in an equation for total number of collisions per unit time per area: This quantity is also known as the "impingement rate" in vacuum physics. From the kinetic energy formula it can be shown that where "v" is in m/s, "T" is in kelvins, and "m" is the mass of one molecule of gas. The most probable (or mode) speed formula_26 is 81.6% of the rms speed formula_27, and the mean (arithmetic