michael rauls
Tech Sergeant
- 1,679
- Jul 15, 2016
Wow....... could you expand on that a bit?Chris, I agree but there is a subtlety here in that definition that is causing all the problems and that I think is going to cause further problems and confusion. We never had a problem with something like PSI because it was clearly understood that P - for POUNDS represented a FORCE supplied by the billions upon billions molecular collisions with the container walls. In the same way it was visually obvious that POUNDS as WEIGHT was also a FORCE which was measured by either the compression or stretching of a spring or springs attached to a dial called a SCALE. You can directly feel the force you have to apply to compress a spring. So weighing an object is an opposition of forces. The force of gravity pulling down and the spring force pulling up. The same is true everywhere on the planet. The ground/floor HAS to push up on your feet, chairs push up on your behind, motors supply force to lift you into the air, the muscles in your legs supply force to lift you up stairs, etc.
Electronic scales have a platform that is attached to a piezoelectric crystal. The force deforms the crystal changing its electrical resistance which can be measured.
In all of the above it is easy to envision that transported to the moon, Mars, Jupiter the FORCE applied by the new gravitational field would change the force applied by gravity and thus the scale reading. You can call the scale readings by any names you want but they represent FORCE/WEIGHT
Now the QUANTITY of matter is MASS and unless you alter the object in some way THAT remains constant anywhere in the universe. So we need a device that does not rely on FORCE like a Scale. We use a BALANCE which is in essence an glorified Teeter-totter a Double Pan Balance in the lab. The unknown mass on one pan and Known masses on the other pan util we get a balance. The sum of the known masses now must equal the unknown. Once again the name you give the numbers on the known masses can be anything you want but in SI we use GRAMS a unit of MASS or QUANTITY of matter. The English/US Customary system brought in the SLUG as their unit of MASS. As long as science remained isolated everytng was fine but as science became international the two systems collided causing considerable problems
Bear with me, I'm getting there. When the old English system was in full force the US/UK part of the world resisted any Continental influences as lead by the French, i.e. that evil Metric System. [N.B. - The English refused to accept the Gregorian Calendar (it was Popish) of 1582 until 1752 at which time England and the US were ELEVEN days ahead of the rest of the western world]. So scientific measurements were conducted in the FPS system or FOOT-POUND-SECOND system in the British influenced world. As the Metric System gained traction it never supplanted the old English so Physical Laws and calculations could and were carried out in one of three systems FPS - CGS - MKS. And at times the systems crossed one into the other so we had to express Kilograms/grams into Pounds - Mililiters/Liters into Gallons/Quarts - Cubic centimeters/cubic meters into cubic inches/cubic feet. We memorized or carried around lists of "CONVERSION FACTORS like, e.g. 1 Kilogram = 2.2 Pounds BUT, BUT, BUT it was clearly understood that this was an EQUIVALENCE NOT AN EQUALITY. In other words BIRDS have WINGS and so do airplanes; Tables have LEGS and so do Horses/dogs/people BUT you would NOT for an instant suggest that they are THE SAME thing
So yes it is certainly true that a 100 kilogram MASS placed on a spring scale will cause the dial to read 220 POUNDS at or near the Earth's surface. That makes them EQUIVALENT in that situation not identical. So it is an unfortunate consequence of human resistance to change that POUNDS exist at all and that they have morphed into Pound-mass and Pound-force. The very fact that you have to hyphenate them tells you that they are NOT the same things
