Gene Mechtly wrote in USMA 11660: >On Thu, 15 Mar 2001, Joseph B. Reid wrote: >> ... If the life jacket had a flotation power 61 N at sea >> level, it would have a flotation power of only 60.93 N at Denver. > Do you assume total immersion of the jacket at both locations? >The newton (N) is the SI unit of force. Why do you call it power? > >> However, at sea level and 45° latitude the life jacket would support >> (float) a mass of 6.22 kg, and at Denver it would still float a mass of >> 6.22 kg. > How so? What fractions of immersion do you assume for the jacket, >and for the floated mass at each location? > >> Hence the flotation power should have been expressed in kilograms.or >> pounds-mass. > How so? In SI, neither force nor mass is power. > > Furthermore, Archimedes' Principle (governing flotation) applies >directly to forces not to masses. I apologize for my sloppy terminology. "Flotation force" or "flotation ability" would have been better. I assumed that the life jacket would be totally immersed in fresh water, both at Saint John and Denver. As you point out, Archimedes principle applies to forces, i.e. weights in the scientific sense. At Saint John the life jacket has a flotation force of 61 N, from which I deduce that it will support when totally immersed a mass of 6.22 kg. At Denver its weight will be only 60.93 N, but by Archimedes principle the weight of the water displaced will also be 60,93 N. On the moon the weight of the water displaced would be only about 10 N, and so the flotation ability of the life jacket would be only 10 N. But at Saint John, Denver, and on the moon, by Archimedes principle the mass supported would be 6.22 kg. The weight of the object supported and the weight of the water displaced vary in fixed proportion from Saint John to the moon, but the mass of water displaced and the mass of the object supported remain constant. Joseph B. Reid 17 Glebe Road West Toronto M5P 1C8 Tel. 416 486-6071
