|When you heat a marshmallow why does it expand?
At first it expands, because it is full of air,
and the air expands.But it is porous, so the air
eventually escapes, and then the marshmallow just
melts, and gets all gooey, because sugar has a
very low melting point. Also, marshmallows have
gelatin, which also melts easily. They turn black
when you catch them on fire, because that is also
the sugar burning. If you burn sugar in a spoon
over an open flame, it will also melt, boil, and
eventually get black. That's the carbon left over!
Most objects expand on heating, but usually solids
expand less than liquids, and both expand much
less than gases, which expand a lot. Fill a
balloon with air and put in the refrigerator. It
will shrink down when it has cooled. Take it out
and it will swell up again.
solids, but they contain lots of air, and it is
the air that expands so the Marshmallow swells up.
If you rip open a marshmallow and look at it with
a magnifying glass, you can see that it has a lot
of little holes in it. Each of these holes is
filled with air. When you put the marshmallow in
the microwave, you cause the air in each hole to
heat up. Hotter air pushes outward with more
pressure, so it pushes on the walls of the holes
and the holes expand --especially because the
heating also makes the marshmallow material softer
and stretchier. This process is similar to blowing
air into a soap bubble.
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