- Let say that I have two different gases
at two different temperatures
that just got in contact with each other.
So, this is my magenta gas.
Right over here, let me draw a bunch of
the molecules of my
magenta gas right over here.
And it's just, this system over here,
I guess, whatever you want to call it,
has just come in contact with this blue gas.
This blue gas, right over here.
And lets say that right where when we're starting
our simulation, our experiment,
that this magenta gas has a higher temperature.
Higher temperature.
And our blue gas has a lower temperature.
Lower temperature.
So lets just remind ourselves what temperature is.
Specially if we think about it on a molecular scale.
So higher temperature, lower temperature.
Temperature is proportional to average kinetic energy.
So these molecules, they're gonna be vibrating around,
they're gonna be bumping around.
They're gonna have,
each of them are gonna have kinetic energy
and if you average them,
that's gonna be proportional to temperature.
So let me depict each of this individual
molecule's kinetic energy.
Maybe this one is doing that.
Maybe this one is going in this direction.
Maybe that one is going that direction.
That one is going in that direction.
This is going in that direction.
That is going in that direction.
So,
notice, they all have different directions.
And the magnitude of their velocity can be different.
They all have different speeds.
They all might have different speeds.
So they have different speeds right over here.
And they're all bumping into each other.
Transferring their kinetic energy,
transferring their momentum
to from one particle to another.
But when we talk about temperature
we talk about the average kinetic energy
or what's proportional to the
average kinetic energy of the system.
Well this one, each of these molecules
are also gonna have some kinetic energy.
But on average it's gonna be lower.
Maybe this one is doing something like this.
This one is doing something like this.
This is doing something like this.
So they're different,
but on average they're gonna be lower.
So,
hopefully you see that this magenta arrows
are bigger than these blue arrows
that I'm doing.
And they don't all have to be,
for example this one
might have a lot of kinetic energy.
But when you average it out,
the average here is gonna be lower than the average here.
So, just like that.
Now, if this is our initial state,
what do we think is going to start happening?
Well, before our different groups of gases
were colliding with itself
or the magenta was colliding with the magenta.
The blue is colliding with the blue.
But now they're gonna start colliding with each other.
And so you can imagine when
this molecule right over here,
collides with this molecule,
it's gonna transfer some kinetic energy to it.
So after the collision, this one might be going.
After the collision.
So lets just say they just bounced in to.
So this is right before,
and lets say they just finished bouncing into each other.
So right after they finish bouncing into each other,
this one might ricochet off.
So this one is going to go this way.
Let me do this in a different color.
So it might hit this one, bounce off,
and then transfer some of its kinetic energy
and then it bounces off in this direction.
While this one, after the collision,
after the collision is going to
is maybe going to move
much faster in this direction.
And so notice, you have a transfer of energy.
Just with that one collision you had
a transfer of kinetic energy
from this molecule to that molecule.
And this is going to happen throughout the system.
That the faster molecules, the ones with more kinetic energy
as they collide you're gonna have transfer of energy.
So you're gonna have a
transfer of energy from the higher temperature
to the lower temperature.
Transfer, transfer of energy.
And this transfer of energy.
And you can consider this transfer of thermal energy,
we're talking about temperature here.
So, the things that are related to temperature,
we would say thermal.
So these, this is transfer of thermal energy.
Transfer of thermal energy.
The amount, so you're gonna have,
if you're gonna start with higher energy here.
You have higher average kinetic energy.
You have lower average kinetic energy here.
But this is going to transfer energy
from the magenta to the blue.
It's gonna go from higher temperature
to the lower temperature.
And that energy that's being transferred,
that energy that's being transferred,
we call that, and this is a word that you
have probably heard many times in your life,
we call that energy that's being transferred,
we call that heat.
That literally this hotter gas over here
is heating up.
Is heating up this cooler gas.
And the way that this transfer of
thermal energy is happening
where it's through the collision of the particles,
the transfer of kinetic energy to the collision of particles
that's transferred momentum,
we call this conduction.
We call this thermal conduction,
or I'll just call it conduction.
Let me write thermal conduction.
I'll do it in a new color.
So this that is being described is thermal conduction.
Which is a way that many times
you have experienced heat being transferred.
For example, you probably have had
the experience of,
if you take a, I don't know,
you take a pot.
Lets say you take a pot like this.
Lets say it's a cold pot at first.
So its particles, the particles in the pot
have a lower kinetic energy.
So I'm not gonna be able to do all of them.
And then you put it over a fire.
You put it over a fire.
Let me see if I can draw it.
You put it over a fire.
So this is the fire, this is the fire.
And we're talking about really
just heating up the metal of the pot,
I'm not even concerned about what's in the pot right now.
So this fire is going to heat up,
it's gonna heat up the bottom of this pot first.
And it's actually gonna do it primarily
through thermal conduction,
because fire is nothing but super hot air particles
and those super hot air particles
are gonna bump in to the metal particles of your pot.
So these metal particles of this pot,
they're kinetic energy is going to start going up.
So this part of the pot is going to start heating up.
And right when you turn your stove on,
the top of the pot might still be cool,
but the bottom is going to get hot very fast.
But if you just wait a few minutes,
these metal particles are gonna keep bouncing
and vibrating into each other.
And so eventually, the top over here
is going to get quite hot.
Is going to get quite hot.
And the way that the top of this metal got hot
it was through thermal conduction
that the metal of the bottom got hot first,
and then they bounced into their neighbors,
or vibrated into their neighbors
and transferred some of that kinetic energy.
And so once again you see this transfer of heat
from a higher temperature region,
to a cooler temperature or lower temperature region.