Effusion is the process in which a gas escapes through a small hole. This occurs if the diameter of the hole is considerably smaller than the mean free path of the molecules. According to Graham's law, the rate at which gases effuse (i.e., how many molecules pass through the hole per second) is dependent on their molecular weight. Gases with a higher molecular weight effuse more slowly than gases with a lower molecular weight; the number of smaller molecules escaping will be greater but the mass of the larger molecules will be greater. For two gases at the same temperature , and thus having the same kinetic energy, the root mean square molecular speed, , of each gas can be found using the equation