Let's start with an illustration
here we have hot and cold blocks of some material
they each have a thermometer in them
If we put them together,
Let's take a look!
you can see that there has been a transfer of energy
from the hot block to the cold block
resulting in the same temperature for each!
and it is important to remember that the temperature is the average kinetic energy of a substance,
in contrast with heat which is the flow of kinetic energy.
So what direction does heat flow?
You're right! always from hot to cold.
This is a basic fundamental law of the universe.
But how does that happen? What is happening at the particle level?
And another interesting question to ponder is
Will there still be any heat flow now once the two blocks have reached the same temperature?
We will address that question a bit later.
So to understand heat we need to
understand how particles are involved in the flow of kinetic energy.
Let's back up a bit.
Starting with hot and cold again let's see what's happening
between the hot and cold blocks.
using a magic bus.
As we zoom in you can begin to see the particles that make up the two blocks.
The kinetic energy is shown as vibrational motion.
The lower block in red has greater vibrational motion: it has a higher average kinetic energy
and therefore a higher temperature.
The upper block and blue has less vibrational motion: it has a lower temperature.
What happens when a slow-moving particle hits a fast-moving particle?
There is a transfer of kinetic energy!
And how does that affect their temperature?
Yes the cooler particle becomes warm the hot particle becomes cool.
Let's look again as we put the blocks together so the surface particles are in contact.
The collisions constantly transfer kinetic energy which is depicted here with the particles
becoming purple and reaching a more intermediate rate of vibration, or
in other words reaching the same temperature.
Note they need to transfer kinetic energy both between and within each block for this to happen.
Let's get back to a previous important question:
Think about it: the atoms are still constantly colliding and so are constantly transferring
kinetic energy, but there is no net change in temperature.
The two blocks have reached an equilibrium once they reach the same temperature.
The amount of heat going from upper block to lower is equal to the amount of heat going from
the lower block to the upper block.
the rate of kinetic energy transfer between the blocks is now equal,
which defines the equilibrium!
an important thing to mention is how the surface is being portrayed here which is as a very smooth unblemished surface.
In reality at the particle level we would see an irregular surface
with peaks and valleys, where only small localized contact between the
two substances would occur and transfer kinetic energy.
and yes these particles are all vibrating they have kinetic energy
but I will let you use your imagination for that.
What is interesting about the gaps is that there are
air molecules trapped in them which we see here.
The air molecules will act as an intermediary,
colliding with an absorbing kinetic energy from the high kinetic hot particles,
and then colliding with and transferring that kinetic energy
to the slower cold particles and increasing their temperature.
Eventually the two blocks come to the same average kinetic energy, shown here as violet particles.
So this video so far has demonstrated one of the three categories of heat
which we call heat conduction: a transfer of energy through the collisions of particles.
There is also radiant heat and convection heat which
we will briefly touch in the next two slides.
Radiant heat is energy transfer through electromagnetic radiation, which is light.
When photons are absorbed their energy is transferred to the absorbing body,
increasing the kinetic energy of its atoms.
and of course we can't miss this opportunity to show a partial dextro-eclipse!
Now on to convection
all of which is beyond the scope of our video.
This has been a mad scientist production.