Re: [Phys-L] physics and potatoes

["Anthony Lapinski" <Anthony_Lapinski@pds.org>]

Here's Hewitt's answer from the Instructor's Manual:

The main reason for serving potatoes wrapped in aluminum foil
is to increase the time that the potatoes remain hot after being
removed from the oven. Heat transfer by radiation is minimized
as radiation from the potatoes is internally reflected, and heat
transfer by convection is minimized as circulating air cannot make
contact with the shielded potatoes. The foil also serves to retain
moisture.

(Conceptual Physics, 10th ed, Ch 16, Ex 8)


Phys-L@Phys-L.org writes:
> So has anyone done the experiment????
> What did Hewitt say the answer was? 
>
> 1. Trapping the steam is a reasonable answer compared to a lot of the
> others.  Evaporation will certainly cool the potato, but some moisture
> will
> still escape through the folds in the foil.
> 5,6 are also possibilities.
>
> I suspect this is not designed to be a question with a definite answer,
> but
> rather one to promote discussion.
> Foil will also reflect radiation, while the darker potato skin will absorb
> it better, but also radiate it better.
> The type of oven may also be important, electric vs gas vs convection.
> Baking may be assuming it is not a grill.
>
> It has certainly been successful on this list, but much of the discussion
> has not been about resolving which answers make more sense.
>
> The factor of mushy vs crisp skin has certainly gone around, but the time
> to
> cook difference has not been well established.
>
> John M. Clement
> Houston, TX
>
> > I saw a question in Hewitt about why potatoes are wrapped in 
> > foil for baking. I searched online and found some 
> > interesting/conflicting answers:
> >
> > 1. The foil will trap the steam inside, making the potato cook faster.
> >
> > 2. The foil is a good conductor, making the potato cook faster.
> >
> > 3. The foil should be wrapped tightly around the potato to 
> > minimize air inside, which is a poor conductor.
> >
> > 4. Put the shinier side of the foil toward the potato. This 
> > will reflect more heat back to the potato, making it cook faster.
> >
> > 5. The foil does nothing during baking, only to create less mess.
> >
> > 6. The foil does nothing during baking. But after baking, 
> > wrapping a hot potato in foil will keep it warmer because the 
> > foil traps the heat (less energy lost via radiation).
> >
> > etc...
> >
> > I'm a bit puzzled with all of this. Are there multiple ideas 
> > about heat transfer happening here? Has anyone actually tried 
> > this cooking method, and is there a significant difference?
> >
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