hi there my name is Kaylee today we'll be doing a physics lesson on
conservation and types of energy so what is energy we hear about it all the time
people not having enough energy or energy costing a lot of money but what
really is energy energy is the ability to do work
something like jumping or running uses energy the Sun gives off energy even
driving a car takes energy but there's something really special about energy it
can never be created or destroyed ever not in the history or the future of the
world the same amount always exists and that can be a little confusing but
energy can never be created or destroyed it can be transferred so you can think
of energy like a river it's always flowing and moving dirt rock grass fish
and sometimes it move slowly and sometimes water may even stop and pool
and other water may move even faster and create Rapids the two main energy types
we will focus on are kinetic and potential energy and in terms of energy
and physics these are like opposites of each other so kinetic energy is the
energy of something moving and it depends on two important things the mass
or how heavy the thing moving is and the velocity or how fast the thing is moving
at and potential energy is the energy of something at rest that's high off of the
ground or off of your zero point and it depends on two things mass how heavy the
thing at rest is and the height or how high off of the ground the thing is so
this is our energy checklist we need mass and height for potential
energy we need mass and velocity for kinetic energy and if something has mass
height and velocity you can have both types of energies and that's when you're
seeing the transfer or the flow like the river of energy in real time let's use a
skateboarder at rest at the top of the ramp
as an example right now what kind of energy does the skateboarder have well
we know that she has mass because we know that she exists and does she have
height yes she looks very high off the ground to me but does she have velocity
what we said in the beginning that she's at rest so we know she's not moving she
has no velocity so if she does have mass and she does have height but she doesn't
have velocity that means that she only has potential energy right if we use our
energy checklist mass height now let's say she's gone half way down the ramp so
right now what kind of energy does a skateboard have does she have mass yes
we already know she has mass does she have height well she's still pretty far
off the ground so yes she has height and does she have velocity well we know
she's rolling down the ramp so she's probably moving pretty fast
so energy checklist yes for mass yes for height yes for velocity that means she
has potential energy and kinetic energy both of them and she's made it all the
way to the bottom of the ramp and she's gonna be on her way up the other side of
the ramp but right now at the bottom of the ramp what kind of energy does a
skateboarder have so from the checklist yes we know that she has mass does she
have height so right now at the bottom of the ramp she's the same level as the
ground so no she does not have height but we do know that she has velocity
she's still moving right she's probably going pretty fast down here at the
bottom so yes she does have velocity energy checklist
yes to mass yes to velocity kinetic energy it is so now we have the
skateboarder and she's in real time so we can see what happens as she transfers
her energy from potential to kinetic and back again so I'm just going to explain
the layout to you so here we have the ramp here here we have the skateboarder
that's what we saw earlier in the video and then here we have some tools that
we're going to use the first one is the slide bar here you can see I can make
the skateboarder smaller she has less mass and larger she has more mass so I
can change that leave her right in the middle for now I can check this box for
speed that gives me my speedometer so I'm able to tell if how fast she's
moving if she has zero speed and how that changes as she transfers energy and
perhaps most importantly I'm gonna click this bar graph and it's gonna show me a
little graph right here the only thing I'm worried about is kinetic energy
potential energy and total energy I'm gonna pretend like this thermal energy
here doesn't count we don't care about it we're not gonna worry about it so
we're just going to look at how kinetic energy and potential energy transfer
back and forth and if that changes the total energy at all all right let's play
so let's first start with potential energy so let's get our bar graph up
there we'll get our speedometer up there just so that we will know when she has
to go we know that she has mass here from the slide bar let's keep it right
in the middle for now and let's go put her up high and see what happens all
right so right here let's look energy checklist we know that she has mass we
know that she's very high off the ground and let's see potential energy here I
see zero kinetic energy I have zero speed that all makes sense so my total
energy the only energy I have is potential energy checklist let's see
what happens when I change the mass so if I give her less mass
potential energy dropped a lot total energy dropped the same amount because I
only have potential energy and if I make her way bigger potential energy got a
lot bigger total energy got a lot bigger and that's just from changing the mass
so we understand now that checklist mass is important let's put it right back in
the middle and see now height so we kept her up here let's see what if we started
her up here so she's not moving still zero kinetic energy is zero but looking
at potential energy dropped a lot we didn't change the mass this time all we
did was change how high off the ground she is so that makes a lot of sense then
potential energy will change based on how high off the ground we are up high
down low or it will change if I'm a small object with not a lot of mass or
if I'm a big object with a lot of mass cool let's write it right back in the
middle let's put her back up to the top and now let's give her some speed so
we're gonna get her going so we should see the speedometer the red arm here is
gonna go up and we should see kinetic energy kick in and let's see what
happens to this potential energy bar as the kinetic energy kicks in let's see
all right there it is do you see so I'm getting speed I'm going back to zero
getting speed going back to zero getting speed Oh nice I'm gonna give it a pause
right about now so let's see what happens we have speed we have mass so
energy check those that means we do have kinetic energy perfect and we have mass
we know we have height so we know the potential energy and our total energy
here looks like it's bigger than both of these that means we have both energies
right now we have kinetic energy because we have mass and velocity and with
potential energy because we have mass and height off the ground so I'm going
to change this to slow motion now so we can really see how these energy bars
change so I'm going to let her go and there she goes so we see as we
higher off the ground but she grows kinetic energy gets lower
speed is lower and let's see what happens as she was back towards the
bottom she's getting faster so look at she's way faster now our red arm is
higher on the speedometer our kinetic energy is higher and our potential
energy is almost zero because we're almost at the ground nice so this makes
it really clear about how energy transfers our total energy right it
can't be created or destroyed it's always the same and it just transfers
between kinetic energy and potential energy so nice job the next thing that
you should do is go watch the friction and energy video and you'll learn about
how friction changes kinetic and potential energy totals so check that
out and remember to always be clever