Bill Hooper wrote in USMA 11095, and I quite agree: >I agree with gene (below). Explaining that a kilogram of mass and a kilogram >of force are "equal" is like stating that the temperature outside is equal >to my speed if I am driving at 65 mph on a day when it is 65 degrees >Fahrenheit (°F) outside. Does that mean 65 °F "equals" 65 mph? > >The kilogram of mass (the ONLY kilogram there is, in SI) is a totally >different quantity from a kilogram of force (a very NON-SI unit that should >never be used in connection with SI measurents). > >An object has mass. It also has a force of gravity acting on it (usually). >If the mass is measured in kilograms-mass and the force (a totally different >quantity) is measured in kilograms-force (a totally different unit), the >fact that the two measurements may have the same number is irrelevant. > >(Also, it's not always true; it is only true when the gravitational field is >exactly equal to the arbitrarily adopted standard value. That's not >precisely the case even at various points on the surface of the earth, and >certainly is not correct anywhere else, except by purest coincidence.) > >The fact that the kilogram-force is defined in such a poor way (as the force >of gravity on a 1 kg mass) is one of the reasons why the kilogram-force is a >poor choice of unit to use for measuring weight or other forces. But I find it boring because I knew all that decades ago. Joe Joseph B. Reid 17 Glebe Road West Toronto M5P 1C8 Tel. 416 486-6071
