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Re: [Phys-l] Weight?



Are you saying that the supporting force N is related to the object's weight by N3?
Consider that the N3 gravitational force pair would still operate even if the object were in free fall, so that N = 0.



Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://mysite.verizon.net/res12merh/
-----Original Message----- From: Espinosa, James
Sent: Wednesday, November 17, 2010 1:06 PM
To: Forum for Physics Educators
Subject: [Phys-l] Weight?

What is weight? Sometimes, when the origin of the lay word has not been technically defined (as is done in mathematics), it helps to find its etymology. The etymology of "weight" goes back to "lift." It, therefore, appears that the weight of a body has been considered an upward force. I tell my students that weight is a force of support, pointing vertically upward. From Newton's laws it follows that weight is equal and opposite to the force (pull) of gravity on the body. It can then be shown that N = mg. What I emphasize to the students is that mg (pull of gravity) is due to the whole Earth, including India, China, the Pacific Ocean, etc.; but N (the force of support is due only to the floor which is in contact with the soles of the shoes. The agent of the force is completely different on the two sides of the equation. I do not attempt to confuse the students with corrections that might exist from the Earth's rotation, Special Relativity, General Relativity, Quantum
Field Theory, String Theory, or any other such.

James Espinosa
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