in today’s video we’re going to be
taking a look at pulleys one of the
classic six simple machines we’ll take
some measurements demonstrating how they
work and then we’ll try building a scale
model of an electricity free elevator a
pulley is one of what Renaissance
scientists referred to as the six basic
machines six mechanical devices that
help you change the direction or
magnitude of a force the other five are
a lever a wheel and axle an inclined
plane a wedge and a screw today we’ll be
looking at pulleys and taking some
measurements with this fish-scale to see
what happens to the different weights on
a rope as it runs through one or more
pulleys after that the plan is to build
a scale model of something I came up
with a few years ago and maybe other
people have come up with it hundreds of
times before me but the idea is to make
an elevator that uses just weights ropes
and pulleys and no electricity here’s
the idea a fixed weight will have two
separate pulley systems attached to it
one that makes it so you could ride the
other end of the rope up and one that
makes it so you could ride it back down
first off we need a frame that we can
attach stuff to so I’ve got a bunch of
scrap wood and we’re gonna start
[Music]
[Applause]
[Music]
[Applause]
this is not the most official looking
construction ever some pieces are kind
of twisted and warped and it’s just not
flat that’s because this is literally
just thrown together from pieces that
already had just in my scrap pile but it
should work pretty well the important
thing is that this end over here can
take a good amount of weight and we can
do our tests on this here’s the first
pulley we’re gonna do some tests with
it’s designed to just be permanently
attached onto something it doesn’t move
around like some other kinds of pulleys
it just stays in one spot but that’s
exactly what we wanted first we’ve got
our pulley attached and we’ve got a thin
cord running through the pulley we’re
now going to attach that onto this
little clip that’s just to make things a
little bit easier as we’re disconnecting
and reconnecting stuff we have here a
fishing scale we’ve got here what is
supposed to be a 10 pound weight this is
just sort of a barbell exercise weight
we’re gonna just hook that on with this
little rope and see what measurements
our scale gives us ten point one seven
pounds for those who are curious that is
four point six kilos so we can see just
over ten pounds it could be that the
weight has a little bit of extra on it
it could be that this fish scale is not
100% accurate but it’s pretty close it’s
supposed to be 10 pounds it’s showing up
as almost 10 pounds now let’s see what
happens if we connect this to our pulley
system and then use our scale to pull on
that alright let’s add a little bit of a
loop into our rope right here so that we
can hook our scale onto it pull on the
loop weight goes up alright turn our
scale on the scale is going to be
upside-down where we should still be
able to see the numbers so it was ten
point one seven pounds ten point one
seven we got exactly the same readout a
single fixed pulley does change the
direction of the force but it doesn’t
change the magnitude of the force I’ve
now got a seven point five pound weight
with a hook attached to it and we’re
gonna put that through the loop instead
of our scale and what we’re gonna see is
that it’s not heavy enough to pull the
10-pound weight of course it’s not ten
pounds is more than seven and a half
pounds drop it the other way we can see
the ten pound
of course enough to lift the
lighter-weight with our seven and a half
pound weight attached to one end if we
now attach the fish-scale to the same
spot it’s not going to take as much Pole
because it’s already got the weight same
deal we’ve got static friction
coefficient to overcome but we can see
that what we’re getting on the scale
varies between about one and a half
pounds and well I think we got up to six
there but an equilibrium does seem to be
at about two and a half pounds which is
exactly what we would expect to see
let’s change things up and try attaching
a single movable pulley to our weight
instead of one fixed pulley above we’ve
got our 10-pound weight we have a pulley
attached to the top of the weight on one
end our cord is just attached to the
beam it’s not running through this
pulley it’s just on the beam separate
from that and the other side we can just
pull with our hands so how hard are we
gonna have to pull on this rope in order
to get that weight to lift off the
ground well let’s look at it if it’s
just suspended in the air we know we
have ten pounds of weight hanging down
and we’ve got two cords that means each
cord should have five pounds on it and
that’s not really gonna change even if
we’re pulling it up and down we should
still have five pounds are suspended in
this cord and five pounds suspended in
this cord here we go here’s our scale
pull till the weight starts lifting and
we are at about five pounds we pull
really fast for a second in might
register is even higher but for the most
part we get approximately five pounds of
force necessary to lift this 10-pound
weight now with our single movable
pulley system it cuts the weight down in
half but of course there has to be a
trade-off you can see that if I move my
hand I’m grabbing the rope right at the
pulley if I lift it from here all the
way up to this beam the weight didn’t
move the whole distance to the beam the
weight moved half of the distance to the
beam so it only takes half as much force
to lift this weight off the ground but
it only moves half as far there has to
be a trade-off and you can’t remove the
amount of work it takes to get that
weight up to its final height and see
the raise it all the way up my hand has
to travel twice the height of the weight
but now
we have an issue back to where we first
started before we’d even come up with
the pulley in the first place is that
we’re lifting up sure it’s easier to
lift up than it was before but we’re
still pulling up which is not as easy of
a motion as pulling down so we can run
it through the fixed pulley again and
now we can pull down and lift the weight
up the fixed pulley doesn’t change the
magnitude but it does change the
direction so this takes five pounds
pulling up that means this takes five
pounds pulling down and of course if we
move the entire distance from the top
pulley to the bottom pulley our weight
moves approximately half that distance
you have to go back and pull it a second
time to get it all the way up I’ve got a
couple more pulleys so I’m going to add
another one to the top and another one
to our weight and see if we can reduce
how much we have to pull on this even
more
all right the chord starts fixed on one
end of the beam it’s going down through
the first pulley up through the fixed
pulley on the top now we’re gonna come
back down through the second movable
pulley on the weight and then we’re
gonna go back up to this newly fixed
pulley feeling pretty lightweight to me
let’s check how much it takes to move
this with two moving pulleys and two
fixed pulleys
it’s showing up as anywhere between one
and a quarter pounds and almost four and
a half to overcome friction but what we
should be looking at is one quarter of
the total weight that would be two and a
half pounds previously we attached our
seven and a half pound weight to a
single fixed pulley system and of course
the 10-pound weight lifted it right up
but now we’ve got a system of moving
pulleys and we should see the opposite
effect
quite a bit in fact there is very little
resistance there the seven and a half
pound weight just plummets to the ground
lifting the 10-pound weight one quarter
of the distance to the pulleys at the
top several years ago while I was just
doing some doodles drawings messing
around with how pulley systems work I
thought of this idea that you might be
able to use pulleys and weights to build
a sort of elevator the concept I thought
was pretty fun and so what I wanted to
do
is build a scale model and it’s not just
one weight that would lift you back up
it’s a weight that has two separate
systems attached to it one where the
weight is attached to a single fixed
pulley so the weight would pull you up
and another system run at the same time
that has a movable pulley and a fixed
pulley so your weight would overcome the
counterweight and you could ride it back
down we have our system all set up we’ve
got a 10-pound weight with two separate
pulley systems attached to it the black
one is a single fixed pulley so it’s not
changing the magnitude it’s still an
even ten pound pull but it is changing
the direction the weight goes down it
pulls the rope up the movable pulley
changes our magnitude dividing it in
half and the fixed pulley changes the
direction so that it’s still the
opposite direction as the movement of
the weight so imagine that this whole
thing is a scaled-down treehouse this
weight represents the weight this seven
pound weight represents the person or
you know we’ll say me and this
represents the little ledge in the
treehouse of the treehouse itself this
is actually non-functional it’s just
there to prove a point the black cord
which is on the fixed pulley and that is
currently tied to something on the
ground and this little loop is where our
person can grab a hold now as we untie
the rope from where it’s wrapped around
this screw the heavier weight takes over
lifting this weight well almost all the
way up to this platform like I said this
is just illustrative we can just say
that they can climb on from there yay we
have climbed up onto our platform just
as we wanted but now you need to get
down and the weight is all the way down
there so what you do is you clip into
the other system and climb out of the
treehouse
you are now gently lowered down to the
ground by the pulley system and the
weights of course the weight is now only
halfway there and the loop to get back
up is way out of reach so what you need
to do is just keep pulling on the orange
cord lift your weight all the way back
to the top until you can reach the loop
for the other side again this is
actually one set of where you would be
glad that the pulleys aren’t 100%
frictionless if they were perfect
pulleys than these you jumped out of the
treehouse you would actually still drop
at the full speed of gravity you would
hit the ground holding a rope that took
a whole bunch of your weight off so it
wouldn’t be like hitting the ground
full speed normally jumping out of the
treehouse your legs wouldn’t be
supporting your whole weight but it
still probably be pretty scary to be
rushing in at the ground that quickly
overall the idea does work pretty well
and I hope that I get a chance in the
future to try this out as a full-scale
treehouse elevator guys thanks for
watching and we’ve got more for you to
see the box up at the top will take you
to our last video you should go check
that out the bottom box will show you
what YouTube thinks you need to be
watching next and if you hit this bomb
in the middle you’ll be subscribed to
our channel so you never miss out on a
video don’t forget to ring that Bell and
we will see you in the next one talk to
you then [Music]
taking a look at pulleys one of the
classic six simple machines we’ll take
some measurements demonstrating how they
work and then we’ll try building a scale
model of an electricity free elevator a
pulley is one of what Renaissance
scientists referred to as the six basic
machines six mechanical devices that
help you change the direction or
magnitude of a force the other five are
a lever a wheel and axle an inclined
plane a wedge and a screw today we’ll be
looking at pulleys and taking some
measurements with this fish-scale to see
what happens to the different weights on
a rope as it runs through one or more
pulleys after that the plan is to build
a scale model of something I came up
with a few years ago and maybe other
people have come up with it hundreds of
times before me but the idea is to make
an elevator that uses just weights ropes
and pulleys and no electricity here’s
the idea a fixed weight will have two
separate pulley systems attached to it
one that makes it so you could ride the
other end of the rope up and one that
makes it so you could ride it back down
first off we need a frame that we can
attach stuff to so I’ve got a bunch of
scrap wood and we’re gonna start
[Music]
[Applause]
[Music]
[Applause]
this is not the most official looking
construction ever some pieces are kind
of twisted and warped and it’s just not
flat that’s because this is literally
just thrown together from pieces that
already had just in my scrap pile but it
should work pretty well the important
thing is that this end over here can
take a good amount of weight and we can
do our tests on this here’s the first
pulley we’re gonna do some tests with
it’s designed to just be permanently
attached onto something it doesn’t move
around like some other kinds of pulleys
it just stays in one spot but that’s
exactly what we wanted first we’ve got
our pulley attached and we’ve got a thin
cord running through the pulley we’re
now going to attach that onto this
little clip that’s just to make things a
little bit easier as we’re disconnecting
and reconnecting stuff we have here a
fishing scale we’ve got here what is
supposed to be a 10 pound weight this is
just sort of a barbell exercise weight
we’re gonna just hook that on with this
little rope and see what measurements
our scale gives us ten point one seven
pounds for those who are curious that is
four point six kilos so we can see just
over ten pounds it could be that the
weight has a little bit of extra on it
it could be that this fish scale is not
100% accurate but it’s pretty close it’s
supposed to be 10 pounds it’s showing up
as almost 10 pounds now let’s see what
happens if we connect this to our pulley
system and then use our scale to pull on
that alright let’s add a little bit of a
loop into our rope right here so that we
can hook our scale onto it pull on the
loop weight goes up alright turn our
scale on the scale is going to be
upside-down where we should still be
able to see the numbers so it was ten
point one seven pounds ten point one
seven we got exactly the same readout a
single fixed pulley does change the
direction of the force but it doesn’t
change the magnitude of the force I’ve
now got a seven point five pound weight
with a hook attached to it and we’re
gonna put that through the loop instead
of our scale and what we’re gonna see is
that it’s not heavy enough to pull the
10-pound weight of course it’s not ten
pounds is more than seven and a half
pounds drop it the other way we can see
the ten pound
of course enough to lift the
lighter-weight with our seven and a half
pound weight attached to one end if we
now attach the fish-scale to the same
spot it’s not going to take as much Pole
because it’s already got the weight same
deal we’ve got static friction
coefficient to overcome but we can see
that what we’re getting on the scale
varies between about one and a half
pounds and well I think we got up to six
there but an equilibrium does seem to be
at about two and a half pounds which is
exactly what we would expect to see
let’s change things up and try attaching
a single movable pulley to our weight
instead of one fixed pulley above we’ve
got our 10-pound weight we have a pulley
attached to the top of the weight on one
end our cord is just attached to the
beam it’s not running through this
pulley it’s just on the beam separate
from that and the other side we can just
pull with our hands so how hard are we
gonna have to pull on this rope in order
to get that weight to lift off the
ground well let’s look at it if it’s
just suspended in the air we know we
have ten pounds of weight hanging down
and we’ve got two cords that means each
cord should have five pounds on it and
that’s not really gonna change even if
we’re pulling it up and down we should
still have five pounds are suspended in
this cord and five pounds suspended in
this cord here we go here’s our scale
pull till the weight starts lifting and
we are at about five pounds we pull
really fast for a second in might
register is even higher but for the most
part we get approximately five pounds of
force necessary to lift this 10-pound
weight now with our single movable
pulley system it cuts the weight down in
half but of course there has to be a
trade-off you can see that if I move my
hand I’m grabbing the rope right at the
pulley if I lift it from here all the
way up to this beam the weight didn’t
move the whole distance to the beam the
weight moved half of the distance to the
beam so it only takes half as much force
to lift this weight off the ground but
it only moves half as far there has to
be a trade-off and you can’t remove the
amount of work it takes to get that
weight up to its final height and see
the raise it all the way up my hand has
to travel twice the height of the weight
but now
we have an issue back to where we first
started before we’d even come up with
the pulley in the first place is that
we’re lifting up sure it’s easier to
lift up than it was before but we’re
still pulling up which is not as easy of
a motion as pulling down so we can run
it through the fixed pulley again and
now we can pull down and lift the weight
up the fixed pulley doesn’t change the
magnitude but it does change the
direction so this takes five pounds
pulling up that means this takes five
pounds pulling down and of course if we
move the entire distance from the top
pulley to the bottom pulley our weight
moves approximately half that distance
you have to go back and pull it a second
time to get it all the way up I’ve got a
couple more pulleys so I’m going to add
another one to the top and another one
to our weight and see if we can reduce
how much we have to pull on this even
more
all right the chord starts fixed on one
end of the beam it’s going down through
the first pulley up through the fixed
pulley on the top now we’re gonna come
back down through the second movable
pulley on the weight and then we’re
gonna go back up to this newly fixed
pulley feeling pretty lightweight to me
let’s check how much it takes to move
this with two moving pulleys and two
fixed pulleys
it’s showing up as anywhere between one
and a quarter pounds and almost four and
a half to overcome friction but what we
should be looking at is one quarter of
the total weight that would be two and a
half pounds previously we attached our
seven and a half pound weight to a
single fixed pulley system and of course
the 10-pound weight lifted it right up
but now we’ve got a system of moving
pulleys and we should see the opposite
effect
quite a bit in fact there is very little
resistance there the seven and a half
pound weight just plummets to the ground
lifting the 10-pound weight one quarter
of the distance to the pulleys at the
top several years ago while I was just
doing some doodles drawings messing
around with how pulley systems work I
thought of this idea that you might be
able to use pulleys and weights to build
a sort of elevator the concept I thought
was pretty fun and so what I wanted to
do
is build a scale model and it’s not just
one weight that would lift you back up
it’s a weight that has two separate
systems attached to it one where the
weight is attached to a single fixed
pulley so the weight would pull you up
and another system run at the same time
that has a movable pulley and a fixed
pulley so your weight would overcome the
counterweight and you could ride it back
down we have our system all set up we’ve
got a 10-pound weight with two separate
pulley systems attached to it the black
one is a single fixed pulley so it’s not
changing the magnitude it’s still an
even ten pound pull but it is changing
the direction the weight goes down it
pulls the rope up the movable pulley
changes our magnitude dividing it in
half and the fixed pulley changes the
direction so that it’s still the
opposite direction as the movement of
the weight so imagine that this whole
thing is a scaled-down treehouse this
weight represents the weight this seven
pound weight represents the person or
you know we’ll say me and this
represents the little ledge in the
treehouse of the treehouse itself this
is actually non-functional it’s just
there to prove a point the black cord
which is on the fixed pulley and that is
currently tied to something on the
ground and this little loop is where our
person can grab a hold now as we untie
the rope from where it’s wrapped around
this screw the heavier weight takes over
lifting this weight well almost all the
way up to this platform like I said this
is just illustrative we can just say
that they can climb on from there yay we
have climbed up onto our platform just
as we wanted but now you need to get
down and the weight is all the way down
there so what you do is you clip into
the other system and climb out of the
treehouse
you are now gently lowered down to the
ground by the pulley system and the
weights of course the weight is now only
halfway there and the loop to get back
up is way out of reach so what you need
to do is just keep pulling on the orange
cord lift your weight all the way back
to the top until you can reach the loop
for the other side again this is
actually one set of where you would be
glad that the pulleys aren’t 100%
frictionless if they were perfect
pulleys than these you jumped out of the
treehouse you would actually still drop
at the full speed of gravity you would
hit the ground holding a rope that took
a whole bunch of your weight off so it
wouldn’t be like hitting the ground
full speed normally jumping out of the
treehouse your legs wouldn’t be
supporting your whole weight but it
still probably be pretty scary to be
rushing in at the ground that quickly
overall the idea does work pretty well
and I hope that I get a chance in the
future to try this out as a full-scale
treehouse elevator guys thanks for
watching and we’ve got more for you to
see the box up at the top will take you
to our last video you should go check
that out the bottom box will show you
what YouTube thinks you need to be
watching next and if you hit this bomb
in the middle you’ll be subscribed to
our channel so you never miss out on a
video don’t forget to ring that Bell and
we will see you in the next one talk to
you then [Music]
Please follow and like us: