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Re: [Phys-l] Good Questions

But not the result of the experiment to which I referred *. The other reason to wait (to get it colder) is the emissivity. So my question remains has anyone done the xpt?


* Can this cancel the other obvious reason to wait? [Delta T is the other obvious reason to which I referred.]
http://www.madsci.org/posts/archives/2000-09/969405728.Ph.q.html


bc agrees the above is confusing.

p.s. this effect, the delta T one, is commonly called Newton's law of cooling. Why not cooling and heating I don't know.

Jim Krider wrote:

Hewitt has an overhead with this question on it.
Heat flow is proportional to delta T. If you wait to put the cream in
your coffee delta T is large for ten minutes allowing a fast flow of
heat. If you put the cream in right away delta T becomes smaller and
the amount of heat flow is much less for ten minutes.



Jim Krider Laboratory Coordinator Senior

PIRT - Physics Instructional Resource Team

Arizona State University

P.O. Box 8751504 Tempe, AZ 85287-1504

480-727-8391 FAX 480-965-7954 james.krider@asu.edu

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Bernard
Cleyet
Sent: Tuesday, October 10, 2006 10:25 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Good Questions

#3 is the only question I remember from intro Physics in 1955. It was not in the text, but part of a lecture. It was a question going the rounds in the U of Calif. system.

Has anyone done this experiment. I was suspicious as the appropriate emissivity is not in the visible. Can this cancel the other obvious reason to wait?

Note this experiment:

http://www.madsci.org/posts/archives/2000-09/969405728.Ph.q.html

and:

http://www.madsci.org/posts/archives/2000-09/969405728.Ph.r.html


bc



Jeffrey Schnick wrote:


1) Suppose you fire a bullet from a gun, and then, using the same

amount

of gunpowder, you fire a blank from the same gun. In which case is the
recoil greater?

2) (A former member of the College karate club asked me a question that
has resulted in my asking this one in class.) In a karate

demonstration,

you see a person break a stout board with her bare hand. While her hand
is in contact with the board, how does the force of her hand on the
board compare with the force of the board on her hand?

3) (I saw one like this, many years ago in an old thermodynamics
textbook.) You have a mug of coffee but your coffee is too hot. You
want to start drinking it in three minutes. You drink your coffee with
cream. You have just the right amount of cold cream to make the

beverage

have just the right flavor. It takes you 5 seconds to mix in the cream.
In which case would your beverage be cooler in three minutes: Wait 2
minutes 55 seconds and then mix in the cream; or; mix in the cream

right

away and then wait 2 minutes 55 seconds.

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Cliff
Parker
Sent: Saturday, October 07, 2006 6:26 PM
To: Forum for Physics Educators
Subject: [Phys-l] Good Questions




I am looking for good questions...


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