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I think they use some type of glycerol or something (I started
in chemical engineering and knew this at one point) like it with a
freezing point below 0 Celius that helps keep the scoop warm. Because as
Leigh pointed out, solid metal scoops stick to the ice cream.
One wants a freezing point *above* the freezing (or sticking) point
of the ice cream, not below it. The reason is straightforward*. As
the scoop cools it will eventually reach the freezing point of the
liquid it contains. Further use of the scoop will not cool it
appreciably until all the liquid is frozen. The latent heat of
freezing must be extracted before further cooling is possible. Thus
it is desirable to have a liquid with a freezing point at the
desired operating temperature, and with a latent heat as large as
practical, consistent with keeping the mass and volume small. Water
is the obvious choice for this substance, which is why I guessed it.
Ludwik, I've never heard of such an ice cream scoop before. It is a
clever idea. Where does one obtain this device? What is it called?
The patent may be available on the web, and I would like to see it.
Leigh
*When I say "straightforward" I am making a statement about the
manner in which I speak about the physics here. As Jim Green will
recognize I employ the caloric model in this discussion. In that
model heat is considered to be a substance which flows from one
place to another. This pedagogical point I only raise here because
I am now writing a short paper on just this topic which I hope will
be accepted for publication by The Physics Teacher.