Re: [Phys-L] Conceptual Physics Course

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

> -----Original Message-----
> From: phys-l-bounces@mail.phys-l.org 
> [mailto:phys-l-bounces@mail.phys-l.org] On Behalf Of Brian Blais
> Sent: Thursday, May 17, 2012 11:49 AM
> To: Phys-L@Phys-L.org
> Subject: Re: [Phys-L] Conceptual Physics Course
>
> On May 17, 2012, at 11:22 AM, Jeffrey Schnick wrote:
>
> > On a related note, what do you do to convince a person in  
> a lasting 
> > manner that the reciprocal of (1/x + 1/y) is not, in general, x+y?
>
> x=y=0
>
> x=y=one million
>
> these two specific examples show that they aren't even close, 
> and can be done with just a little inspection. I try to get 
> my students to ask a few questions to themselves about any 
> term in an expression or an answer to a problem that they are 
> dealing with:  is the answer greater or less than zero?  is 
> the answer small or large compared to 1?
>
> this allows them to catch many of the silly arithmetic errors 
> that they make, and would easily allow one to check the 
> expressions above.

x=y=0 represents one of the special cases where the two expressions are
equal. I think you might be taking 
the reciprocal of (1/x + 1/y)
to be
(1/x + 1/y) itself.

> 		bb
>
> --
> Brian Blais
> bblais@bryant.edu
> http://web.bryant.edu/~bblais
> http://brianblais.wordpress.com/
>
>
>
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@mail.phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l