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In this video, Paul Andersen explains the different forms and units for energy. A discussion of the laws of thermodynamics is also included. Sample conversion problems using dimensional analysis is also included.
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Transcript Provided by YouTube:
00:03
Hi. It’s Mr. Andersen and this is environmental sciences video 22. It is on energy concepts.
00:08
I was just wondering how much energy it takes to do a Google search. And so what did I do?
00:13
Of course I did a Google search. How much energy does it require? And what you get really
00:18
quickly, the fourth one down, is a document from Google themselves. And they said that
00:23
a typical Google search takes 0.2 seconds and requires 0.0003kWh. So that is fast, but
00:29
I do not know how much energy that is. And so we can use energy concepts to figure that
00:34
out. So that is the energy, and I want to convert it to something that I actually know.
00:38
So how much time could we run a light bulb, a 60 watt light bulb in the same amount of
00:43
energy? So I am going to take the known quantity from Google and doing dimensional analysis,
00:48
so I always put this over 1, and then I am going to look up an conversion because we
00:52
know that 1 kilowatt hour, I am going to put that on the bottom, is equal to 3.6 million
00:58
joules of energy. That is just a conversion between two forms of energy. And so what I
01:03
am doing is I am canceling out the kilowatt hours and now I have converted it to joules.
01:08
That seems like a lot of joules at this point. And now I have to convert that to seconds.
01:13
Well, I know that a watt is equal to a joule per second. And so 60 watts is 60 joules per
01:20
second. So I can cancel out my joules. And now I just multiply everything across the
01:25
top, divided it by everything on the bottom. And I get 18 seconds. Now if that seems hard,
01:30
hopefully as I have gone through this video at the end you could solve a similar problem.
01:34
But what does in mean? One google search is the same as turning that light on for 18 seconds.
01:40
And to me that seems like a lot of energy. 18 seconds is not that long, but it seems
01:45
like a long time, so I am not going to wait that long. So if we look at what energy is,
01:49
energy is the ability to do work or transfer heat. You probably learned this before. It
01:53
comes in two forms. We have potential energy which is due to position. And then we have
01:57
kinetic energy which is due to motion. And so chemical energy, so the energy in a fuel
02:02
for example, is potential energy. It is energy in the bonds of the chemical. And then something
02:07
that is really important, electricity is actually a form of kinetic energy. Energy is conserved.
02:13
It can neither be created nor destroyed. And that is the first law of thermodynamics. And
02:17
the second law of thermodynamics, you should become familiar with, and that is the idea
02:21
that as we convert energy from one form to another we lose energy. That eventually becomes
02:26
heat. It increases the randomness of the universe or the entropy of the universe. The unit of
02:31
energy is the joule but you are going to find tons of different units out there. From the
02:36
kilojoule to the BTU to the therm. And the hard part is you are going to have to make
02:41
conversions between those different forms. And if you have a really good grasp, dimensional
02:46
analysis is really not that hard. Power is the amount of energy that we use for a given
02:51
period of time. So it is the rate of energy used. We measure that in watts. And one joule
02:56
per second is equal to 1 watt. Now you will also see kilowatts a lot of the time. That
03:01
is going to be 1000 watts. And so energy, remember, can be potential or kinetic. So
03:06
if we take this crate and we lift it up, it now has potential energy. It has gravitational
03:12
potential energy. And as we drop it releases some of that energy as kinetic energy. Now
03:17
the box itself still has potential energy. It has energy in the bonds, we call that chemical
03:22
energy. I could release that by, for example, burning it. Another type of kinetic energy
03:27
that is really important is going to be electricity. So motion of those electrons. The key point
03:33
is that energy is conserved. That is the first law of thermodynamics. So if we drive this
03:37
car from point A to point B, we used energy. We did work on that car. Now where did it
03:43
come from? Gasoline. But before that it was in the oil. Before that it was probably in
03:48
some kind of a tree. Before that it was in the sun. So we are just converting one form
03:53
of energy to another. The second law of thermodynamics talks about what happens to that energy as
03:59
we do these conversions. And so we have input energy. And then we are going to have output
04:04
energy. Some of that is going to be useful, energy in the motion of the car. But a lot
04:08
of it is going to be waste energy. It is going to be heat. It is going to be sound. And eventually
04:12
what happens is all of that energy becomes non usable or heat. The first person to really
04:17
figure this out was James Joule. What he did is had an apparatus where he had paddles inside
04:22
water. He would have a weight that fell. And as they spun they heated up the water and
04:27
he could measure that with the temperature. That is why we call it the joule, capital
04:30
J. Another way to think about it is it is the force times the distance. And so imagine
04:35
you take an apple, an apple has a gravitational force of around 1 newton. And you lift it
04:41
1 meter. That is 1 joule of energy required to do that. Now you could move it slow or
04:48
you could move it fast. But if you move it that distance, that is going to be 1 joule.
04:52
How do we tell the difference between moving it fast and slow? That is going to be power.
04:56
And we measure that in watts. That is the amount of joules for a given period of time.
05:00
So let’s say it takes me 2 seconds to lift that apple 1 meter. So how many joules is
05:08
that? Well it is still 1 meter times 1 newton so 1 joule. Since it took 2 seconds that is
05:14
going to be 0.5 watts. What if I lift it in 1 second? That would be 1 watt. What if I
05:20
lift it in 0.5 second? That is going to be 2 watts. And so the amount of power in a 60
05:25
watt light bulb would be like lifting that apple in 0.0167 seconds. So it is a really
05:30
really huge amount of energy. And so there are lots of different forms of energy that
05:34
we have. So to convert between these two you have to know the conversion. It is not something
05:39
you should memorize, but you should be able to look it up. So 1 joule is what we measured.
05:43
It is our base standard SI unit of energy. If we have 1000 joules that is a kilojoule.
05:49
When we are talking about food or the energy found within our food you will see calories
05:52
and kilocalories. 1 calorie is 4.184 joules. But the actual calorie we are talking about
05:59
in our food is a kilocalorie. And so one kilocalorie is going to have 4184 joules. You will also
06:06
see in some air conditioning and heating systems, BTUs or British Thermal Units. So we have
06:12
a conversion here to joules. We could use therms, which are larger amounts. Or we even
06:17
talked about at the beginning these kilowatt hours. All of these, even though it has the
06:21
term hour in it, all of these are measures of energy. It is because we are dividing our
06:27
power by a certain amount of time. When it comes to watts it is a little simpler. We
06:31
have a watt, which is joules per second and then we have kilowatts as well. And so you
06:36
should understand these conversions. I would not memorize them but how to apply it in a
06:40
problem. And so let’s say you are given a problem like this. We have a 75 watt light
06:44
bulb. How much energy would this use in a day, in 24 hours if we left it on? So you
06:50
are going to start with your knowns. So we have a 75 watt light bulb, so I am going to
06:54
put that 75 joules per second. You could pause the video now and try to solve this one on
06:59
your own. But let me show you how to do it. I could work either on the energy side. So
07:05
I could go towards kilojoules or I could go towards hours. I am going to go towards kilojoules
07:09
because I have a conversion up here. I know how I can go between joules and kilojoules.
07:14
And so I could write out that conversion. I am going to put joules on the bottom, kilojoules
07:18
on the top. So I have already moved from joules to kilojoules. You can see my joules that
07:23
cancel. I want to go from seconds to hours. And so how do I do that? Well I know that
07:29
60 seconds is equal to 1 minute. Now my seconds cancel. I could go from minute to hour, so
07:35
I know that 60 minutes is 1 hour. So I have it all the way to kilojoules per hour and
07:40
how many hours does it run? It is going to run for 24 hours. So that is my last conversion.
07:45
So all my units will cancel and I am going to be left with kilojoules at the end. So
07:49
I multiply across the top. Multiply across the bottom. So it is going to be around 6500
07:55
kilojoules with significant digits. And so the best way to solve problems like this is
07:59
to do problems like this. And I will put some links to problems in the video description
08:03
down below. But did you learn the following? Could you pause the video at this point and
08:07
try to answer what is in all of the blanks? So again energy is the ability to do work
08:12
or also transfer heat. It could be potential, which is due to position, or kinetic which
08:17
is due to motion. The unit is the joule but we have all different types of energy forms
08:23
that we can use. So you have to understand not only conversions but how to do the conversions.
08:30
The watt is joules per second. Thermodynamics shows how energy is conserved. We have the
08:35
first and the second. That is energy. And I hope that was helpful.
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This post was previously published on YouTube.
