The heat that drives convection comes from two
main sources: something called primordial
heat and something called radiogenic
heat. Primordial heat is all of the heat left
over from when the Earth formed. Four and a half
billion years ago our planet formed by the
collision of rocks and dust. Over time it grew
from the size of a small rock into our large
planet just from rocks colliding with each other
over and over and over again. This process
generates a lot of heat because each time a rock
hit the growing planet, it transformed its
kinetic energy (the energy of movement) into
thermal energy (heat). So the baby Earth was
really hot and has cooled off over the years
through the processes of convection and
conduction. The deeper you go into the Earth,
the hotter it gets because a lot of primordial
heat remains. The other process that causes the
Earth to remain hot is radioactive decay of
elements like uranium, thorium, and potassium.
These three elements are unstable and can
transform into other elements in a process called
radioactive decay This decay gives off
heat, which causes our planet to stay warm. This
same process happens inside nuclear reactors where
we produce electricity!
Convection requires a warm layer beneath a
cooler upper layer. It does not matter how
the heat gets there. In the atmosphere, it's
because the ground absorbs sunlight (you can't see
through it), while the air does not (you can see
through it), so the air in contact with the ground
gets warmed up faster than the air up above it.
"Heat" is thermal energy on the move.
In order for thermal energy to move, there needs
to be a reason for it to move---this means having
2 locations where one is hotter than the other:
heat spontaneously flows from hot to cold.
One of the ways that thermal energy moves is
through convection, which just means that
there is a fluid that flows to help the
movement of thermal energy from the hot location
to the cold location.
It is hard to specifically answer your
question because the hot location can be
anywhere, or anything, it all depends on the
system you are interested in. I will give you an
You would like to cool down on a hot summer day.
You use an electric fan to cool down. The fan
produces flowing air on your skin, carrying the
heat from your body to the cooler static air in
the room. In this example, your body is the hot
location, the static air in the room is the cold
location, and the flowing air ("wind") on your
skin is the fluid that helps move thermal energy
from your body to cool you down. You can do
this type of analysis on any system that transfers
thermal energy by convection.
Click Here to return to the search form.