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Re: [Phys-l] FW: The "why" questions



?? Hadn't we established that the acceleration of the center of mass begins at the moment that the force is applied and follows F = m a(cm)?

Bob at PC

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Philip Keller [PKeller@holmdelschools.org]
Sent: Tuesday, December 07, 2010 1:13 PM
To: 'Forum for Physics Educators'
Subject: Re: [Phys-l] FW: The "why" questions

Suppose I apply a force to a real body and I am interested in the physics of that finite time interval before a = f/m.

How do I know that I have applied a force? In fact, what IS a force? Halliday and Resnick takes the same approach as Young and Freedman (and others I'm sure): begin by saying a force is a push or a pull, but then continue with an operational definition: "To measure such forces quantitatively, we express them in terms of the acceleration that a given standard body experiences in response to that force." (H & R, I'm looking at the 4th edition)

So my question is: if an object is in equilibrium and then I come along and apply a force (or so I believe), until the object accelerates, how do I know the force exists? Or is the operational definition to include the word "eventually"?

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
bounces@carnot.physics.buffalo.edu] On Behalf Of D.V.N. Sarma
Sent: Monday, December 06, 2010 9:12 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] FW: The "why" questions

For real bodies a = F/m is acquired only after
a finite interval of time.

regards,
Sarma.
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Forum for Physics Educators
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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l