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