Final answer:
The measure of speed or kinetic energy of molecules in Physics is related to their motion and is calculated using the root mean square speed, which depends on the temperature and is the same for all molecules at a constant temperature.
Step-by-step explanation:
The measure of the speed (or velocity or kinetic energy) of the molecules is a concept within the field of Physics, particularly in the study of thermodynamics and kinetic molecular theory (KMT). For instance, at room temperature, the average speed of an air molecule is about 500 m/s, and this, combined with the molecule's mass, contributes to its momentum. Moreover, the average kinetic energy and the root mean square speed (urms) are related to the temperature and are independent of the type of molecule. The urms is calculated as the square root of the average of the squares of the speeds and is an estimate of the molecules' speed that informs us about their kinetic energy.
Expressing mass in kilograms (kg) and speed in meters per second (m/s) yields energy values in joules (J), and when dealing with gases, the averages of both speed and kinetic energy for a large number of molecules are considered. For example, the rms speed of a nitrogen molecule (N2) at 25 °C is significant and reflects in phenomena like the speed of sound. Lastly, the equation K = KBT shows that the average kinetic energy per molecule depends only on the absolute temperature.