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Re: [jt512] Kilonewtons? a question for those who understand physics:
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glytch
Oct 9, 2007, 10:41 PM
Views: 846
Registered: Aug 29, 2006
Posts: 194
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In reply to: But the balloon doesn't have negative weight either, so your example did not even support the incorrect point you were trying to make. Jay, you are one stubborn dude. As rgold, climb_eng, ptlong, gunkiemike, valarc, and others have said quite clearly, if you express a force as a 'kilogram of force', what you're saying is that that force is equal in magnitude to the force that a kilogram exerts on a scale at the earth's surface. You're assuming that a certain mass (in kg) is accelerated at a specific rate (acceleration of gravity at the earth's surface); that gives you the m and the a in F = m*a. You then refer to the force, F by the mass, m, assuming a constant a. What I was pointing out (as ptlong and gunkiemike were noting as well), is that such an assumption can be misleading. ptlong referred to inconsistencies between gravity at the poles and the equator, and gunkiemike to the fact that buoyancy in air can foil naive force measurements as well. The point here is that the notion of a 'kilogram of force' necessarily makes assumptions about acceleration due to gravity at the earth's surface based on the fact that a kilogram is a unit of mass; these assumptions may not be well-defined or as straightforward (and therefore as reliable) as they may appear.
In reply to: Unbelievable. After your argument has been refuted repeatedly, you still you're "technically correct?" Jay Yup, you're right. I'm wrong and nobody agrees with me. Especially not those with well respected opinions in these parts. A sampling:
curt wrote: And no, a kg can not be used as a unit of force without assuming some things not explicit in the actual definition of a kg.
rgold wrote: Best to keep the ideas separate, even if the fact that mass and weight are proportional near the surface of the earth allows us to confuse them.
(This post was edited by glytch on Oct 9, 2007, 10:45 PM)
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Post edited by glytch
() on Oct 9, 2007, 10:45 PM
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