Video Transcript

Hello. My name is Walter Unglaub, and this is the basic unit for mass. So in classical physics and most sciences we tend to use the international system, SI system. And here this conventionally the MKS system of units in which M stands for meters, K stands for kilograms and S stands for seconds. So the basic unit for mass would be the kilogram. Alternatively there's also the CGS system, under the SI set of units. And C is centimeters, G is grams and S is seconds. But kilograms is the primary unit for mass that is used in physics for example. If we consider atomic systems, or in chemistry we would like to use the units of atomic mass units or AMU for short. And 1 AMU is defined as 1/12th of the mass of a carbon 12 atom. And this is approximately equal to 1.66 times 10 to the negative 27 kilograms. So it's a very small number. If we go to atomic physics or sub-atomic physics a more appropriate or natural unit of measure for mass is actually a unit of energy. We know from Einstein's energy mass equivalence formula, E equals mc squared, that the rest mass of a particle can actually be formulated in terms of rest mass energy, where the speed of light squared is the conversion factor. Therefore, the standard unit of energy in sub-atomic physics, is the electron volt. And we see this because the mass can be written as the energy divided the speed of light squared. So this electron volt mass it's understood that we're dividing by the speed of light squared. So are the different common units for mass in physics and in chemistry and related sciences. My name is Walter Unglaub and this is the basic unit for mass.