Energy, Work and Power

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Mr. Andersen defines the terms energy, work and power. He also uses a simple example to calculate both work and power.
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Transcript Provided by YouTube:

00:04
Hi. It’s Mr. Andersen and today I’m going to talk about energy, work and power.
00:10
Now what is something that has energy? It’s a pretty big term. So what things have energy?
00:15
Well we would say something in motion or something due to its position. We could say that electricity
00:20
is a form of energy. We could say that matter can contain energy within its chemical bonds.
00:26
Or light has energy. Or sound has energy. So that’s a lot of different things. What
00:30
is energy? Energy therefore is the ability to do work. Well that’s one of those definitions
00:36
that requires us to dig a little bit deeper. What is work? Work in science is simply a
00:41
force times a distance. So anything that can apply a force over a given distance is said
00:48
to contain energy. And we measure that in joules. So work is measured in joules. And
00:55
so let’s give an example. Let’s say for example that you want to take a can of Coke and you
01:00
want to carry it to the top of a set of stairs. Well that can of Coke has 4.0 newtons of weight.
01:08
And let’s say that you have to climb up a set of stairs that is 3.0 meters high. Now
01:14
the interesting thing is that since the gravitational force is always acting down, it doesn’t matter
01:18
if you get to the top of the stairs by walking upstairs or get to a similar distance by climbing
01:24
up a ladder. Or simply just throwing the can of Coke up to that point. If you’ve moved
01:29
it up a certain amount of distance, we’ll call that 3.0 meters, then you’ve done 4.0
01:36
newtons times 3.0 meters or 12 joules of work to get that to the top. Now you could get
01:43
that to the top in a couple of different ways. Let’s say that we were to gradually make our
01:48
way to the top of the stairs. Or we were to run up the stairs. Well we would be doing
01:53
the same amount of work depending on if we were running or going slowly. And so we need
01:58
another term to figure out how fast we’re doing that. And that’s called power. And so
02:03
power is defined as the amount of work in a given period of time. So let’s say that
02:10
you were to go up that set of stairs with that can of Coke. And you were to do that
02:14
in 1.0 second. Well the amount of work we have is going to to be 12.0 joules. And the
02:22
amount of time is going to be 1.0 second. And so the power of that is going to be 12
02:28
watts or w-a-t-t-s or watts is going to be the amount of power that we have. If you were
02:34
to do that slower, so let’s say we were to do that in 10 seconds, then the amount of
02:38
watts would drop form 12 watts to 1.2 watts. So that’s really not that much power. And
02:45
so the amount of power that we’re actually used to dealing with here in the US is horsepower.
02:50
And so horsepower is measured, it measures the amount of work that we can do in a given
02:55
period of time. We use it in engines for example. And so the conversion is 1 horsepower is roughly
03:02
746 watts. And so let’s go back to that problem. If we’re able to move a can of Coke to the
03:08
top of the stairs in 1.0 second we say that that’s 12 watts. So if we convert that to
03:14
horsepower then we are at 0.0040 horsepower machine. So that’s not a very powerful machine.
03:22
Now the one thing that you should realize is not only are we moving that can of Coke
03:26
to the top of the stairs. But we’re also moving our weight, our whole body to the top of the
03:30
stairs. And so maybe we’re a little more powerful than we think.