Re: [Phys-l] Good Questions

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

I tried it in the kitchen.  I put two very small glasses, each
containing 25 ml of whole white milk in the refrigerator.  I poured 350
ml of coffee into each of three white ceramic mugs lined up on my dining
room table from left to right as viewed from my position at the table.
(Each mug then contained 350 ml of coffee.)  I put a kitchen digital
thermometer probe in the middle one.  (The thermometer reads to the
nearest degree Fahrenheit.)  Then I got one of the glasses out of the
refrigerator, and dumped the milk from it into the left mug.  I stirred
it briefly with a spoon which was only in the beverage while I was
stirring.  Then I briefly stirred the coffee in the middle mug with the
thermometer probe and took a reading.  It was 188 degrees F.  A little
bit more than 10 minutes later it was reading 152-154 degrees F. (I
didn't write the temperature value down.  Nor did I keep perfect track
of the time.)  At that time I went to the refrigerator and got the other
glass of milk, poured it into the right mug and stirred it briefly with
a spoon which I promptly removed from the mug.  I took the thermometer
probe out of the middle mug, put it in the right mug and stirred
briefly.  The thermometer read 145 degrees F.  I put the thermometer
probe in the left mug and stirred briefly.  The thermometer read 147
degrees F.  I left the thermometer probe in the left mug, stirring
occasionally, until the reading went down to 145 degrees F. Then I put
the probe in the right mug, stirred briefly, and took another reading.
It read 143 degrees F.  The right mug was cooler.  That is, I find that
if you wait 10 minutes and then pour the milk in, the coffee is at a
lower temperature than it is if you pour the milk in and then wait 10
minutes.

-----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 1:25 PM
> > > 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