<P> No name has yet been given to the unit of mass and, in fact, as we have developed the theory of dynamics no name is necessary . Whenever the mass, m, appears in our formulae, we substitute the ratio of the convenient force - acceleration pair (w / g), and measure the mass in lbs. per ft. / sec. or in grams per cm. / sec. . </P> <Table> Three approaches to units of mass and force or weight <Tr> <Th> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> Base </Th> <Th_colspan="2"> Force </Th> <Th_colspan="2"> Weight </Th> <Th_colspan="4"> Mass </Th> </Tr> <Tr> <Th> 2nd law of motion </Th> <Th_colspan="2"> m = F / a </Th> <Th_colspan="2"> F = W ⋅ a / g </Th> <Th_colspan="4"> F = m ⋅ a </Th> </Tr> <Tr> <Th> System </Th> <Th> BG </Th> <Th> GM </Th> <Th> EE </Th> <Th> </Th> <Th> AE </Th> <Th> CGS </Th> <Th> MTS </Th> <Th> SI </Th> </Tr> <Tr> <Th> Acceleration (a) </Th> <Td> ft / s </Td> <Td> m / s </Td> <Td> ft / s </Td> <Td> m / s </Td> <Td> ft / s </Td> <Td> gal </Td> <Td> m / s </Td> <Td> m / s </Td> </Tr> <Tr> <Th> Mass (m) </Th> <Td> slug </Td> <Td> hyl </Td> <Td> pound - mass </Td> <Td> kilogram </Td> <Td> pound </Td> <Td> gram </Td> <Td> tonne </Td> <Td> kilogram </Td> </Tr> <Tr> <Th> Force (F), weight (W) </Th> <Td> pound </Td> <Td> kilopond </Td> <Td> pound - force </Td> <Td> kilopond </Td> <Td> poundal </Td> <Td> dyne </Td> <Td> sthène </Td> <Td> newton </Td> </Tr> <Tr> <Th> Pressure (p) </Th> <Td> pound per square inch </Td> <Td> technical atmosphere </Td> <Td> pound - force per square inch </Td> <Td> atmosphere </Td> <Td> poundal per square foot </Td> <Td> barye </Td> <Td> pieze </Td> <Td> pascal </Td> </Tr> </Table> <Tr> <Th> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> Base </Th> <Th_colspan="2"> Force </Th> <Th_colspan="2"> Weight </Th> <Th_colspan="4"> Mass </Th> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul>

Why is the unit of mass called fundamental unit