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Course: Biology library > Unit 7
Lesson 2: Laws of thermodynamics- Introduction to energy
- Types of energy
- First Law of Thermodynamics introduction
- Introduction to entropy
- Second Law of Thermodynamics
- Second Law of Thermodynamics and entropy
- Why heat increases entropy
- The laws of thermodynamics
- Energy and thermodynamics
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First Law of Thermodynamics introduction
The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. For example, kinetic energy may be converted into thermal energy, or potential energy may be converted into kinetic energy. Energy is never "lost"—it is transferred or converted in some way.
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- Why can't energy be created or destroyed? Doesn't the sun create light energy or when we are coasting on a bicycle don't we create kinetic energy?(23 votes)
- The sun doesn't create energy. It simply chemically changes hydrogen atoms into helium atoms through a process of Nuclear Fission. The byproduct of this reaction is a massive volume of light and heat energy.
Bicycles don't create kinetic energy. We give the bike kinetic energy by pedaling the bike.(48 votes)
- energy can be destroyed or created.does it mean that "heat energy" can be transformed into a more useful type of energy that has the ability to do work? thus decreasing the level of entropy in the universe after all energy can be transformed from one form to another(25 votes)
- It depends on what you mean by 'heat energy'. If you mean there is a temperature difference between things, then yes, you can use that energy and convert it to a different form (this happens for example in a power station). However, when we talk about thermodynamics, 'heat' often describes energy lost to surroundings by increasing the random motions of molecules. Although energy can be converted from one form to another, it cannot be converted back and forth any way you want. For things to go forward, you need to have an increase of entropy in the universe (this is the second law of thermodynamics), and there is no way you could collect back all the heat energy that has been dissipated into lots of molecules. If you think about a fridge, you can decrease energy of molecules inside it, but at the cost of increasing entropy by increasing heat outside it.(8 votes)
- At, if the light heats up the glass bulb, then how is it intact? Shouldn't the glass overheat and explode? 4:27(7 votes)
- The light doesn't actually heat up anything too much, and since the glass is transparent, barely any heating will occur. The light will simply pass through the glass. If you were talking about the heat from the filament, it would disperse slowly through the collisions of molecules and get more and more dffused with each collision, so it wouldn't heat up the glass much. Even if it did, the heat would quickly disperse out through the glass, without heating it much, as Sal mentioned at. 4:26(2 votes)
- If energy can not be created or destroyed, what energy was there before the Big Bang?Energy has to be created,but only once.Because the energy has to be there for the big bang to happen, right?(7 votes)
- Well if you agree that there was absolutely nothing before the Big Bang, we may well say that none of the laws of conservation were applicable (in this context the law of conservation of energy which says energy can neither be created nor be destroyed), hence we may say that matter could be formed and that's exactly where the matter that exploded during Big Bang came from.(4 votes)
- what is the difference between Radiant energy & Light energy??(2 votes)
- Radiant energy refers primarily to energy that radiates from the source, which is commonly in the form of light energy or thermal energy, while light energy is specifically electromagnetic.(8 votes)
- is thermal energy and kinetic energy the same thing ?(3 votes)
- According to what I've read thermal energy is a somewhat ill-defined property for which usage varies.
You are correct in thinking that a significant fraction of what is usually meant by thermal energy is due to kinetic energy at the atomic level. However, kinetic energy is typically used to describe the energy associated with "organized" motion through space, while thermal energy is "disorganized" motion and also includes vibration and rotation.
An example might be if you kicked a stone out of the edge of a fire. It has kinetic energy imparted by your kick and thermal energy imparted by the fire. The thermal energy from being next to the fire is (mostly {I think}) expressed by enhanced vibration of the minerals within the rock. My understanding is that, while this thermal energy is kinetic (due to movement), it is qualitatively different from the kick imparted kinetic energy.
The following links have more details:
https://en.wikipedia.org/wiki/Thermal_energy
https://www.physicsforums.com/threads/difference-between-thermal-and-kinetic-energy.322759/
https://www.quora.com/Is-heat-energy-basically-just-kinetic-energy(4 votes)
- I had thought that einstein discovered that energy could be converted into matter, and vice versa. Does this mean that, to keep the first law of thermodynamics, all matter is a form of energy?
If this is the case, what are the implications for quantum physics? Does this have something to do with particle-wave duality?(3 votes) - If energy can't be created nor destroyed than how did the energy form for the first time ?(2 votes)
- The conservation of energy has to do with symmetry of time invariance. The conservation of energy comes about because the laws of physics do not change based on the passage of time.
If you have an isolated closed volume of space and you take the sum of all of the energy in a volume of space at time 0s it has to match the sum of all of the energy in a volume of space at time 1s.
When we are dealing with the big bang we do not have an accurate description of the physics that were involved so the symmetry of time invariance may not hold.
Also based on the current observations of the universe and and current theories there is a way for the universe to have come into existence without requiring any energy. Just like stretching a balloon creates an amount of potential energy the stretching of spacetime is similar but with gravitation this can be offset with the introduction of mass so in the initial big bang the buildup of energy from the expansion of spacetime produced the matter and radiation we see around us.(4 votes)
- Isn't Sal confusing the 1st Law of Thermodynamics with the Law of Conservation of Energy? They're different things, the latter pertains to mechanics and the relation of kinetic and potential energy, the former actually states that the internal energy of an isolated system is constant. Yes, they're similar, but mechanics doesn't account for heat as energy transfer, only work, and thermodynamics develops internal energy as the sum of heat and work done on or by a system.(3 votes)
- What kind of energy, does our body generate on a normal basis?
Like, when we walk or jump.(2 votes)- We are not really 'generating' energy, we are using energy (chemical energy stored in food) and converting it into another form. As Davin commented, we convert a lot of energy to heat. But since you ask about walking or jumping, if you are moving, you are converting energy to kinetic energy. And if you jump or climb up a hill, you need to use a source of energy to gain gravitational potential energy. Does this answer your question?
And in case you are wondering where the energy from the food comes from, it all (indirectly), comes from the light energy from the sun. Plants capture this energy and use it to drive chemical reactions that make sugars from CO2 and water, producing sugars and oxygen. Normally that chemical reaction would go the other way, but it is the light energy that makes allows the plant to produce sugars. Then by 'burning' the sugars, we can release energy again, this time not as light, but in a way the lets our body do chemical reactions, and somewhere down the line this for example makes our muscles move. But we can't use all the energy in a productive way, some is always lost as heat.(2 votes)
Video transcript
- [Voiceover] Let's now explore the first law of thermodynamics. And before even talking
about the first law of thermodynamics, some
of you might be saying, "Well, what are thermodynamics?" And you could tell from
the roots of this word. You have thermo, related to thermal, it's dealing with temperature. And the dynamics, the
properties of temperature, how do they move, how
does temperature behave? And that's pretty much
what thermodynamics is, it's about, it's the study
of heat and temperature, and how it relates to energy and work, and how different forms of energy can be transferred from one form to another. And that's actually the heart of the first law of thermodynamics
which we touched on on the introduction to energy video. And the first law of
thermodynamics tell us that energy, this is an important one,
I'm going to write it down, energy cannot be created or destroyed. Cannot be created, or destroyed. It can only be converted
from one form to another. It can only only be converted only be converted, I'm having trouble writing today. Converted from one form, from one form, to another. Or you could transfer it
but you're not going to, you're not going to create or destroy it. And the whole thing that
I, the rest of this video I just want to really
have you internalize that, and I want to look at a bunch
of examples and think about, well, what is the energy
that we're observing, or that we're seeing in a system? And then thinking about
where is that energy coming from, to appreciate
that it's not just coming out of nowhere,
and that it's not just disappearing, it's not
getting destroyed either. And so let's start with
this example of a lightbulb. And I encourage you to pause this video, think about the forms of
energy that we can see here, and then think about where
is that energy coming from, and where is it going? Well, the most obvious form
of energy that you see here, and this, the whole point of a lightbulb, is you see the radiant energy, you see the you see the electromagnetic
waves, the light, being emitted from it. And that light, so this is radiant energy. Radiant energy. And that radiant energy, is due to the heat in the
filament right over here, as the electrons go through
it, it generates heat, so you have thermal energy. So you have thermal energy as well. Thermal energy. But where does this radiant and thermal energy come from? Again, first law of
thermodynamics it tells us, it's not just being
created out of thin air, it must be converted or being
transferred from some place. Well, I just gave you a
hint, this thermal energy is due to the electrons
moving through the filament. They're moving through
the filament which has some resistance, and that generates heat. So the electrons are moving through this, and as they move through that
resistor, they generate heat. So you actually have the
kinetic energy of the electrons. I'll just write KE for
short, kinetic energy of the actual electrons. Well, where is that
kinetic energy coming from? Well that's coming from
the potential energy. You know maybe this thing is plugged into, is plugged into a socket of some kind. So let me draw a little electric socket right over here. And the electric socket, I'll draw, the electric socket if
this is the electric socket in your home, there is an electrostatic
potential between these two terminals. And so when you make a connection, the electrons are able to move. And we'll get into the
details of AC and DC current in the future, but there's
an electrostatic potential, from this point to this
point if we assume that's the direction that the
electrons are going in. And so that, it's that
potential energy we convert to this kinetic energy of the electrons, which is really in the form of a current, and then that gets converted
into thermal energy and radiant energy. Now what happens after, let's
say you unplug the light, the light goes dark, what
happened to all of that energy? Is it still there? Well yeah, that thermal
energy is going to continue to dissipate through the system. And this right over here
would be an open system, it's going to, the air inside the lightbulb,
you can't fully see the lightbulb right here, but
it looks something like this. That's going to heat up, but
then it's going to heat up the glass surrounding the lightbulb, and that's going to heat
up the surrounding air. So the thermal energy is
going to be transferred, and that radiant energy
is going to move outward. And it could be used, it
could be converted into other forms of energy, most
likely thermal energy, it is also probably going
to heat up other things. Well, what about a pool table? When I hit a, if I hit a pool, a billiard ball or a pool
ball right over here, well, where is that energy going? Well some of that energy
might be going to go hit the next ball, which might
go to hit the next ball. But as we all know, if
we've ever played pool, at some point they're going to stop. So what happened to all of that energy? Well, while they were rolling, there was some air resistance, so they're bumping against
these, the air molecules, and it's really friction due to air. And that energy is essentially going to be converted to heat. And one trend that you're going to see very frequently, is as systems progress, a lot more of the energy
tends to turn into heat, rather than doing useful work. And so you're going to
have, as the billiard balls move, there's the air,
and so that's going to be, that's going to be converted,
some of that kinetic energy is going to be turned into heat energy. You're also going to have friction with the actual felt on the table. And that friction, you're
going to have molecules rubbing up against each other, that's also going to
be converted into heat. And so that, because that
kinetic energy gets sapped off, gets keeping sapped
away from the friction, which is essentially
converting the kinetic energy to heat energy, eventually you won't have any more kinetic energy. Now what about this weight lifter here? He's using the chemical energy in his, in the ATP in his muscles,
that converts into kinetic energy that moves his muscles, that moves this weight, but
once he's in this position, what happened to all of that energy? Well, a lot of that energy is
now being stored in potential. it's the potential energy,
he's got this big weight, he's got that big weight above his head, and if he were to just let
go, that thing would fall, I wouldn't recommend he do that, but that thing would fall quite fast. And so now it's all,
or a lot of it has been stored up in potential energy. But he would have also generated heat, his muscles would have generated heat. Even the act of moving it
through the air is going to be some heat in the air,
some friction with it. And so I want you to appreciate
that this energy is not coming out of nowhere,
it is being converted from one form or another,
or being transferred from one part of the system to another. Now we can look at these
examples over here. Same thing with our
runner, what happens after, you can buy the fact that
okay, his chemical energy is allowing his muscles to
move, and that's turning in his kinetic energy for his
entire body, his body is moving, but at some point he stops,
where did all that energy go? Well, some of it will be
heat in his body that's being dissipated into the broader
system, into the air. And also, when he was running,
there was this contact with the ground, that's
going to make the molecules of the ground vibrate a
little bit, some of it will be transferred as sound, so the air particles moving through the air, and
a lot of it will be heat. And we're going to see that
over and over and over again. The diver up here, you have
mostly potential energy. Then it converts to
kinetic energy as he's, as he gets almost in the water. But what happens once
he falls into the water? Well, then that energy's
going to be transferred, as you're going to have these
waves of water move away. And it will also increase
friction, so, well actually he would have had
friction as he fell down, so that would have generated some heat, and there would have
been also some heat with the friction with the water,
you normally don't think of friction with the water,
but there is some friction with the actual water, and there's also, these waves, you have
higher kinetic energy of the actual water
being transferred outward from where he actually dropped in. And I could keep going on and on. You have the chemical potential
energy of the fuel here being, you have combustion occurring, and then that gets converted
into the thermal energy, and the radiant energy of
what we associate with fire. And that doesn't disappear, it just keeps radiating outwards, the radiant energy just
keeps radiating outward, maybe it might heat up something. And the thermal energy will
just keep radiating outward, or I should say, the thermal
energy will just dissipate outward, and heat up the things around it. Same thing with our lightning example. You start with the
electrostatic potential, where the bottom of the
clouds were more negative, and then the ground is positive as well, and at some point, that
potential energy turns into kinetic energy as the electrons
transfer through the air, and then that gets converted
into, or a good bit is going to be converted to
heat and radiant energy. So the whole point of this
video is, no matter what example you look at, if you
think about it carefully enough, and I encourage you to do
this in your everyday life, the energy isn't just coming out of, you know, magically appearing, it's just being converted
from one form to another.