hi there my name is Kaley this is a physics lesson on friction and the
energy due to friction in the real world we know that a skateboarder can't roll
forever yes she will get tired but there's also something that naturally
slows her down but what is that thing it's called the friction and friction is
a force that stops things from moving thinking about pushing a toy car on a
thick carpet or trying to ride your bike on the sand these surfaces have a lot of
friction and make it hard to move there are some surfaces that have more
friction and some that have less so we already talked about the two services to
have a lot of friction so things like thick carpet and sand but what are types
of surfaces that would have less friction or make it easier to move on
how about shiny wood floors think about how easy you can slide across them in
your socks or a frozen lake or ice skating rink you can glide right across
and that means that there's little or no friction on those surfaces but friction
can also show up as energy and remember energy can never be created or destroyed
but there is something else that's special about friction when it shows up
as energy let's do an experiment I want you to take your hand and you're
gonna bring your palms together like you're going to clap and now you're
gonna take them and you're gonna rub your hands really fast back and forth
really fast keep it going do you hear my hands four five four three two and one
did you notice anything if your palms got hot from moving them back and forth
that's friction energy it shows up as heat and it's also called thermal energy
to remind you that it shows up as heat and just like kinetic energy and
potential energy thermal energy has a checklist so that we know if it exists
the checklist is two surfaces like our two hands or car tires in the road and
we need speed or movement between those two surfaces like how we rubbed our
hands together or how car's tire will roll down the road but how do we
transfer kinetic energy to thermal energy think about when we rubbed our
hands together and we used friction to make heat you used kinetic energy by
moving your hands and that kinetic energy was turned into thermal energy or
heat that you felt let's look at another example say you're going to push a toy
car just one push and you're gonna lift your hand away so that the car will roll
on its own what will happen model roll for a while and then it's gonna stop and
that's because you gave the car kinetic energy when you pushed it and the car
has mass and speed but the car also had two surfaces the tire and the floor that
were rubbing against each other and the car moved for when you pushed it and
even though you probably didn't feel it or notice it a tiny amount of heat came
from the friction of the tires in the floor rubbing together and that's what
happens when there's thermal energy heat shows up and it slows it down so let's
take these ideas of friction and thermal energy back to our skateboarder and we
can see what happens when there's potential energy kinetic energy and
thermal energy all in one all right so we're back to our skateboarder and
remembering our ramp here in our skateboarder here and most of our tools
here are the same we have our mass slide bar we can make her smaller or bigger or
heavier lighter we've here in the middle we have our
speedometers we can know how fast she's going and then we have our bar graph
here so now we are gonna be worried about their water G because now we know
what thermal energy is so we're going to look and see how kinetic energy and
potential energy change when there's friction involved and we can make the
ramp either no friction like the first video a little bit of friction or a lot
all right so let's get started it's gonna start out a lot like the first
video when we had no friction present so if we take our escape we're gonna put
her up on the ramp here you'll see she has no speed she's at rest just no
kinetic energy she has no thermal energy because you
have to be moving to have friction present so all of her energy is in
potential energy because she is high off of the ground all right so we've put our
friction slide right here about in the middle so let's see what changes as
friction on the ramp shows up as thermal energy so there's going to be heat from
her tires the wheels here rubbing on the ramp and that'll be thermal energy and
we'll see if it slows her down and ends up stopping her so let's see what
happens so there she goes she has speed she has kinetic energy but look at this
there's also thermal energy that's kicking in here that red bar and I
thought red bar gets bigger both of these are getting smaller so let's try
it one more time and let's do it in slow motion this time
we're gonna take her we're gonna put her up at the top again let's see we're
gonna do it in slow motion so only potential energy what happens she's
going to the minute she starts to go we see a tiny bit of that red bar kinetic
energy let's see it's going it's slowing down a little bit that thermal energy is
getting bigger kinetic energy is getting smaller so now thermal energy is beating
both of them it's higher there it is all right so let's try it one more time
let's watch her speed bar here so we're gonna put her back up here same thing
potential energy to start now instead of paying attention only to the bar graph
here let's look at the speed and see what happens to the speedometer so she's
going she's getting kinetic energy she's making all the way up to halfway up the
speedometer what happens the next time she goes she's only about here let's see
can she make it there again nope only about here what's gonna happen to the
next time only to here so see how she's getting slower her speed is not picking
up to the same level that it was so remember that's kinetic Energy's being
transferred to that thermal energy and then she can't ever come back to that
potential energy because she's not getting that high on the ramp because she
doesn't have the speed to get back up there sound see we're gonna let her come
all the way to a stop she's almost there and look at what's happening thermal
energy is now the total energy there's just barely any left
she's almost down look at she's almost going only to zero and look at that
thermal energies right there at the top so friction thermal energy actually
slowed her all the way down to a stop and all of that energy all that kinetic
and potential energy that she had has been dissipated has shown up as heat in
the system so let's go one more time this time let's make her
friction be a lot and see if it changes what happens so we're letting her go
same thing kinetic energy as she goes down potential energy comes back look at
this time the thermal energy is growing even faster so the ramp is even harder
to move on so instead of getting about six or eight passes she's only getting
about four and then she she has to stop there's so much friction
that she's stopping even sooner and let's see what happens this time if we
make it really low friction so now she's barely any friction and she started out
only potential energy up there let's see kinetic energies going pretty high just
a little bit each pass as she goes she gets speed the thermal energy comes up
Wow so it's going a lot slower so she's gonna be able to do more passes on the
ramp because there's less friction so it's easier to move this time she's able
to get almost as high on the ramp as the time before so her potential energy is
coming back up it's just getting a little bit lower as this thermal energy
bar raises and as the friction turns to heat because she's moving so that
kinetic energy is turning into thermal energy nice so good so now as as these
ideas are starting to make more sense the next thing we're going to do is talk
about the mathematical equations that go along with energy so they each have
their own equation here kinetic potential and thermal so make sure you
watch those videos next the equations for the different energies and remember
to always be clever