|If you could somehow create a 'vacuum' around your
home, would that stop the transfer of heat and
cold in and out of the structure?|
|Question Date: 2016-07-27|
1) It would help a lot, but not entirely. Heat
is transferred through a few basic mechanisms —
conduction, convection, and radiative.
Conductive heat transfer happens when
energetic (hot) molecules bump into less energetic
(colder) molecules, which heats them up.
Convection happens when warm material
physically moves — like when air blows, or water
flows, carrying the heat along with it. If you
were to make a vacuum around your home, you’d
prevent conduction or convection — because there
would be no material for the heat to transfer
through! The third mechanism, though, is
radiative heat transfer. This is heat that
is carried in electromagnetic waves (like
light). You know how much hotter it feels in
the sun than in the shade? The temperature of
the air is no different; the difference is that
you are feeling the radiant heat of the sun. (And
remember, that heat came all the way from the
sun, through the near-vacuum of space…)
One way to reduce radiant heat transfer is
literally to use mirrored surfaces that ‘reflect’
the heat away.
The strategy you described is basically how a
thermos works — they are made with a near
vacuum inside the walls of the bottle, which
prevents conductive and convective heat transfer.
Some are even metallic and reflective, to reduce
the radiant heat transfer as well. And many
high-end experiments in physics that require very
low temperatures (like 4 degrees above absolute
zero, for liquid helium, or even thousandths of a
degree Kelvin) use large, souped-up thermoses as
one of many steps in keeping the room heat from
entering the experimental chamber.
NO. Heat is transferred in three ways: 1.
conduction by the collision of atoms or
by the vibration of the atomic lattice in
solids, by 2. advection or the transport of
heat by material flow (hot air transport heat
upwards) and by 3. radiation. All bodies at
temperature greater than 0 kelvin emit photons
that carry energy. Now, in a vacuum, methods 1 and
2 cannot operate. But radiation always does!
Heat is defined as energy which is stored as
molecular motion—molecules flying around in gases,
churning in liquids, or vibrating in solids.
Objects gain or lose heat, and therefore molecular
motion, in three ways: conduction, convection,
and radiation. Conduction and convection both
rely on matter surrounding the object. Conduction
occurs when an object touches another solid of a
different temperature, like touching a hot plate
to a cold table. The molecules vibrating in the
hot plate bump against the molecules in the cold
table and transfer heat until the plate and the
table are at the same temperature. In convection,
the surrounding material is a fluid instead of a
solid, like submerging the hot plate in a bucket
of cold water. Now, the molecules in the water can
take energy from the plate and get swept away,
letting new cold water molecules interact with the
Finally, radiation is the transfer of heat
energy by emitting light. All objects emit light,
but whether you can see the light depends on the
temperature of the object. At room temperature,
the light emitted is infrared, which is not
visible to humans. As an object gets hotter,
it begins to emit light that we can see, which is
why molten metal glows. Even hotter, and the
object will emit ultraviolet light (which is why
too much sun exposure can give you a sunburn).
Since conduction and convection depend on
material surrounding the object, they would not
occur if your house was in a vacuum. However,
the house would still slowly heat up or cool down
due to radiation.
It's true that heat cannot conduct through
vacuum, since conduction only happens when
molecules collide. In fact, thermos containers
and some insulated windows trap a layer of vacuum
between two walls (perhaps glass or metal) to
reduce heat transfer by conduction.
But even if you could prevent all heat
conduction, there is another way to transfer
heat: radiation. All solid objects release
heat through thermal radiation, which can travel
through vacuum. Black objects radiate more heat,
as do hot objects. If an object becomes extremely
hot, it even starts to glow from all of the energy
it is radiating. We call that object
incandescent, and this is how incandescent
light bulbs work.
The light from the sun is also due to
incandescence, in this case from the incandescent
plasma on its surface. So even a
vacuum-sealed home would receive heat energy from
sunlight or other radiation.
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