During a recent trip to Mexico, I bought a pot that I
would like to hang in my front window. The problem is
that the pot is heavier than I thought it would be when I
was negotiating with the vendor. I haven't weighed it,
but I make it out to be about 25 pounds. Add the weight
of the plant, the water, the mix, etc, and it gets pretty
heavy.

So, I've been thinking. What if I distribute the weight?

I could hang it off a hook and anchor it to the window
sill. By my logic, half the weight would go to one place,
the other half would go to the other place.

Am I wrong?

I also don't know whether it makes any difference how high
the anchor is. I used to know these rules, but I have
forgotten them.

--
Harry

[On Wed, 10 Mar 2004 11:08:49 GMT, Jim Elbrecht
wrote:]

The block & tackle plan would be interesting as a conversation piece,
but I'm betting you can put a 1/4 inch stainless eye bolt in a joist
& be rated for 4-500 pounds with no danger of someone unhooking 1/2 of
your contraption & being hit on the head with pottery.

That's probably what I'll do in real life.

--
Harry

"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a hook or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
felt by the rope at the cleat will be 40 lbs.
Greg

There is no need to go thru all this elaborate pulley system. Get youself a
good 3/8 inch eyebolt lag screw make sure it goes into a ceiling joist at least
2 inches and you can hang 250 lbs on it. Lets not go crazy here !

(The Other Harry) wrote:

During a recent trip to Mexico, I bought a pot that I
would like to hang in my front window. The problem is
that the pot is heavier than I thought it would be when I
was negotiating with the vendor. I haven't weighed it,
but I make it out to be about 25 pounds. Add the weight
of the plant, the water, the mix, etc, and it gets pretty
heavy.

So, I've been thinking. What if I distribute the weight?
-snip-

The block & tackle plan would be interesting as a conversation piece,
but I'm betting you can put a 1/4 inch stainless eye bolt in a joist
& be rated for 4-500 pounds with no danger of someone unhooking 1/2 of
your contraption & being hit on the head with pottery.

Jim

In article , (The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

Well I misread that whole thread!

The original post said "I could hang it off a hook and fasten it to the
window sill".

Which I took to mean; "I could hang IT off a hook 'AND' also fasten IT to
the window sill". 'IT' being the pot? Right?

So, some of the weight would be hanging from the hook and some of the
weight, IT (the pot), being fastened to the window sill, would be taken by
the window sill!

So I started thinking about the diameter and weight of the pot and the
leverage due gravity on a cleat fastened sideways to the window sill....!
But;

It wasn't that complicated at all! Although the thought of a multi pound pot
swinging up against the window sill on a windy night?

Visions of someone out there in their pajamas trying to unhook that pot in
the pouring rain .................! Maybe an anchor or two, laterally would
be a good idea?

BTW 'pot' did refer to the container not the contents? :-)

(Doug Miller) wrote in message . com...
In article , (The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

I suspect your 55 lb reading was while lifting thus getting friction
force added to the weight. Let it all come to rest and you will be
seeing 28 lbs (plus weight of rope from spring hood to the load).

Harry K

"Greg O" wrote in message ...
"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a hook or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

--------40----top-------------
/\
/ \
20/ \20
/ \
load/40 \anchor
------------bottom-------

--------------------top--------------
\anchor /anchor or pulley
\ /
\20 /20
\ /
\ /
\/
40
load with pulley
--------------------bottom----------

Harry K

(Doug Miller) wrote in message . com...
In article , (The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

You bet. Another way of thinking about it: instead of standing on the
other end, what if you hung another 28 lb toolbox on it as a
counterbalance. Obviously then the balance will show the combined
weight. Well, the balance doesn't care whether it's tied off or
holding a counterweight, it sees 28 lb tension in each of the two legs
of rope.

Now suppose you'd paid an engineer to design a hook in the middle of
your ballroom ceiling to hold a quarter-ton chandelier, and then
decided later to hang it with a rope over a pulley ...

Chip C

Harry K wrote:
(Doug Miller) wrote in message . com...
In article , (The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

I suspect your 55 lb reading was while lifting thus getting friction
force added to the weight. Let it all come to rest and you will be
seeing 28 lbs (plus weight of rope from spring hood to the load).

Nope, he got it right. Consider the reversed situation: a rope fixed to a
ceiling, running down to a pully attached to a load and then up to another
hook. The tension in the rope is going to be half the load, since it's
supported by two ropes and the load is equally supported. This is the
exact same situation with a single overhead pully lifting a load: The
force at the ends of the rope are half the force on the pully, or, force
on the pully is twice the load, which isn't suprising: if you wanted to
use free weights to simulate the loading, you'd have to put a 40lb wieght
on the other end to support the 40 lb pot with a total weight supported of
80lb.



John
--
Remove the dead poet to e-mail, tho CC'd posts are unwelcome.
Ask me about joining the NRA.

Harry K wrote:
"Greg O" wrote in message ...
"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a hook or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

--------40----top-------------
/\
/ \
20/ \20
/ \
load/40 \anchor
------------bottom-------

--------------------top--------------
\anchor /anchor or pulley
\ /
\20 /20
\ /
\ /
\/
40
load with pulley
--------------------bottom----------

Look at you're top picture again. How is a 40lb pot supported by a single
rope with only 20lb of tension in it? A: it's not supported at all, and
behaves like an unsupported 20lb weight.


This is what the situation really looks like:
--------80----top-------------
|\
| \
40| \40
| \
load|40 \anchor
------------bottom-------

This way, if you look just at the load, you see a 40 lb weight balanced by
a 40lb tension in the rope.

Now, your diagram was interpreted as a rope going up through a hook and
then back down to the load, then you'd be closer to right like this:
--------40----top-------------
/\
/ \
20/ \20
/ \
/load 40 \
------------bottom-------

Where now you don't have a seperate anchor, and the load is being
supported by two ropes.



John
--
Remove the dead poet to e-mail, tho CC'd posts are unwelcome.
Ask me about joining the NRA.

Hey, mike, you're confusing the issue! If you have 500 pounds hanging on a
block and tackle, it doesn't matter how many ropes, the screwhook at top is
still holding 500 pounds (and now I'm confusing the issue).

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"Michael Daly" wrote in message
...
On 8-Mar-2004, (The Other Harry) wrote:

I could hang it off a hook and anchor it to the window
sill. By my logic, half the weight would go to one place,
the other half would go to the other place.

Am I wrong?

Unfortunately, yes. You've got the general idea, but you're
applying it wrong.

The key is to support the _load_ with several lines through
block and tackle. The lines that run from the top block
to the lower divides the load.

The one that you pull on does not support the load if it
comes off the top block. It only supports the load if it
pulls up from the bottom block. So, if you're pulling
down on the rope, ignore it in determining how many lines
divide the load. If you're pulling up, include it.

One pulley at the top isn't going to help you. It results
in only one supporting line, hence the rope has to be pulled
with full weight of the load.

If you use two, single-sheave blocks, you can arrange it to
halve the load. Run the rope from an eye down thru the
bottom block, back up to the top block and then down to be
pulled on. This results in two lines supporting the load and
half the force in the rope.

Note that the object supporting the top block and eye will
have to support the force in _three_ lines - the two lifting
the load and the one you're pulling down on. This means
that the support is carrying up to 1.5 times the weight of
the load (depending on the angle you're pulling at).

Mike

Let me confuse you further. You want half the weight on the window sill, and
half on the rope?

How about if the rope is too long? Then all the weight is on the window (and
the rope is loose and droopy). How abut if the rope is too short? Then all
the weight is hanging, and the pot is up off the window sill.

I think you better think it out again.

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"The Other Harry" wrote in message
...
During a recent trip to Mexico, I bought a pot that I
would like to hang in my front window. The problem is
that the pot is heavier than I thought it would be when I
was negotiating with the vendor. I haven't weighed it,
but I make it out to be about 25 pounds. Add the weight
of the plant, the water, the mix, etc, and it gets pretty
heavy.

So, I've been thinking. What if I distribute the weight?

I could hang it off a hook and anchor it to the window
sill. By my logic, half the weight would go to one place,
the other half would go to the other place.

Am I wrong?

I also don't know whether it makes any difference how high
the anchor is. I used to know these rules, but I have
forgotten them.

--
Harry

"Harry K" wrote in message
...

I am assuming you have a rope attached to the pot, that runs up to a
hook or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension,
(weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.



Wanna bet?
Greg

"Stormin Mormon" wrote in message
...
Hey, mike, you're confusing the issue! If you have 500 pounds hanging on a
block and tackle, it doesn't matter how many ropes, the screwhook at top
is
still holding 500 pounds (and now I'm confusing the issue).

--


Stormy, you have proven again, without a doubt that you do not know what you
are talking about!
In a situation I described, the hook in the ceiling will feel 2 times the
weight of the flower pot. If you use a more complex block and tackle, one
with several pulleys top and bottem, the more wraps and pulleys you use the
lower the load on the hook in the ceiling, but it will never be less than
the weight of the flower pot, plus the weight of the block and tackle and
the force needed on the rope to suspend the object.

The only way to have less load on the hook than the object weighs is to use
a pulley and the flower pot, and two hooks on the ceiling. then each hook
will hold 1/2 the weight.

If anyone fails to understand this, do as another poster did and get a fish
scale, a pulley, a weight, and a pice of rope, and try it your self!

Think of ot this way, the pot weighs 40 lbs. If you had a pot hanging on a
length of rope hooked to the ceiling, the rope, hook and all feel a load of
40 lbs. If you add pulley at the ceiling and run the rope over it and back
down, you need to apply a force of 40 lbs to suspend the pot, any more or
less force applied and the pot will go up or down. Now you have TWO 40 lb
loads, the pot, and the force to ballance the weight of the pot, which will
be equal. In this case 40 lbs X 2 = 80 lbs.

Another way is to think of this whole rope and flower pot situation as a
tetter-totter. You have a 40 lb kid on one side, so you need a 40 lb kid on
the other side to balance it. The weight the fulcrum of the tetter-totter
feels is 80 lbs. Asssuming the tetter-totter weighs nothing.

One 40 lb kid is the flower pot, the other 40 lb kid is the force on other
end of the rope needed to suspend the pot, and the fulcrum is the pulley or
hook.

Tomorrow night we will discuss complex block and tackles, test at 10 PM!!
;-)
Greg

[On 11 Mar 2004 07:41:35 -0800,
(Harry K) wrote:]

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

This is what I think. I still do.

I can see how where the the hooks are placed might make a
difference, but I can't see how 40 pounds would ever go to
80. Not without something else happening.

I'll test it.

--
Harry

On Thu, 11 Mar 2004 20:57:31 -0500, (The Other
Harry) wrote:

| [On 11 Mar 2004 07:41:35 -0800,
| (Harry K) wrote:]
|
| Wrong. The tension on both sides will be equal (20 lbs) and the top
| hook will feel 40lbs. There is nothing being added to the 40 lbs to
| increase it to 80. I think you have confused the effect of a pulley
| which, when rigged right, will cut the lifting force by 1/2.
|
| This is what I think. I still do.
|
| I can see how where the the hooks are placed might make a
| difference, but I can't see how 40 pounds would ever go to
| 80. Not without something else happening.
|
| I'll test it.
|
| --
| Harry

If the pulley is fixed overhead and one is pulling on the end of the
rope passing over the pulley to lift the weight, it is exactly the
same as if you were standing overhead lifting the weight directly. It
is (in this case) 40 pounds either way. The weight of the object being
lifted using the first class pulley is not "split" into 20 lbs and 20
lbs. It is all one rope and all 40 lbs. The fact that you are using
the pulley merely changes the direction you have to pull. In some
cases this is more convenient, but the work and the weight is the
same.

To summarize:

The weight of the object is 40 lbs.
The weight on the rope is 40 lbs.
The weight on the hook is 40 lbs.
A first class pulley does not "split" the weight, nor does it give any
mechanical advantage. To raise the weight one foot, you pull the rope
one foot using 40 lbs of force.

If you were to attach the pulley to the weight, however, and tie the
rope overhead, and stand above the weight and pull on it, the lift
force on each side of the rope would be half the weight of the object
being lifted. You would have to pull with a force half as much as the
weight. In the example, the object weighing 40 lbs could be lifted
with a pull of 20 lbs of force. The other leg of the rope attached
overhead (above the weight) would be holding the other 20 lbs (the
ceiling holds 20 and you hold 20). You will have to pull the rope two
feet to raise the weight one foot. This is a 2:1 mechanical advantage.


If you add an additional pulley to the ceiling, you can now lift from
below, which is more comfortable. But you gain no additional
mechanical advantage beyond the 2:1 ratio.

However, if you add yet another pulley to the ceiling and run the rope
through it and then through the 3rd pulley (we now have one end of the
rope anchored, two ceiling pulleys, and one pulley on the weight) you
will then again halve the force needed to raise the pulley. Instead of
taking 20 lbs of force to raise a 40 lb weight, it now will take 10
pounds. Each segment of the rope now bears 1/4 of the weight but must
be pulled four feet to raise the weight one foot. The total weight on
the ceiling is still 40 lbs.

The problem everyone seems to be having is that there is no mechanical
advantage to using a first class pulley, so no force is shared. It is
the same as if you picked up the rope and lifted the weight directly
without using a pulley. There is only mechanical advantage -- shared
forces -- using the pulley attached to the weight, or using compound
pulleys such as in a block and tackle. Using the single pulley
attached to the ceiling, the force required is all on your side. The
weight cannot pick up or hold itself or half of itself -- or indeed
any of itself. The weight supported by the ceiling hook and pulley is
the full 40 lbs of the weight.

Here are some diagrams:

http://www.wcsscience.com/pulley/page.html

HTH.

If you guys had been paying attention in third grade instead of
throwing spitballs .... :-)

In article , (Harry K) wrote:
(Doug Miller) wrote in message
. com...
In article ,
(The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from
the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

I suspect your 55 lb reading was while lifting thus getting friction
force added to the weight. Let it all come to rest and you will be
seeing 28 lbs (plus weight of rope from spring hood to the load).


Nope. 55 while lifting, and about 53 at rest.

In article , (Harry K) wrote:
"Greg O" wrote in message
...
"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a hook or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

It appears that *you* are the confused one here. A *movable* pulley will cut
the lifting force in half. A *fixed* pulley only changes the direction in
which the force is applied -- and this situation is entirely analogous to a
fixed pulley.

--------40----top-------------
/\
/ \
20/ \20
/ \
load/40 \anchor
------------bottom-------

Nope. You have a major problem he on the left side, a 40-lb weight is
suspended on a rope that has only 20 lbs tension. Doesn't work that way.

Suppose the anchor on the right is replaced by an un-anchored weight. What
weight is required on the right to balance the 40 lb weight on the left?
According to your diagram, the answer is 20 lbs. Now do you see your error?

--------------------top--------------
\anchor /anchor or pulley
\ /
\20 /20
\ /
\ /
\/
40
load with pulley
--------------------bottom----------

Not the same situation.

That is just so wrong.

--

Larry Wasserman Baltimore, Maryland

This kind of stuff is in the first chapter of a basic course in "Static's".
With everything at rest there has to be a balance of Forces in both
Vertical and Horizontal directions. The tension on the rope is a function
of the angle ( from the horizontal) that it is being pulled at. The Vertical
Force to be balanced is the downward one of 40 lbs.
Since the weight is split between the two ropes the vertical force is 20 lbs
on each side. The tension of the rope (on each side) can be found by using
the equation:
Sin (angle)= (side opposite/hypotenuse), where the hypotenuse is the rope.
The vertical force (or side opposite) is equal to 20 lbs. since 20 +20=40
The tension on the rope is.
For an Angle=10 deg Tension=115 lbs; Angle 50 deg Tension=15 lbs; Angle =80
deg Tension=20.3 lbs: and if the angle is =90 deg the Tension would be 20
lbs in each side.
Doesn't it make sense that if the rope is nearly horizontal that you'd have
to pull like heck on it to hold up a weight. That's because most of your
pulling is in a horizontal direction and you'd need a very large force in
order to generate the vertical force needed to balance the weight.
MLD



"Tom Miller" wrote in message
...
On Thu, 11 Mar 2004 20:57:31 -0500, (The Other
Harry) wrote:

| [On 11 Mar 2004 07:41:35 -0800,
| (Harry K) wrote:]
|
| Wrong. The tension on both sides will be equal (20 lbs) and the
top
| hook will feel 40lbs. There is nothing being added to the 40 lbs
to
| increase it to 80. I think you have confused the effect of a
pulley
| which, when rigged right, will cut the lifting force by 1/2.
|
| This is what I think. I still do.
|
| I can see how where the the hooks are placed might make a
| difference, but I can't see how 40 pounds would ever go to
| 80. Not without something else happening.
|
| I'll test it.
|
| --
| Harry

If the pulley is fixed overhead and one is pulling on the end of the
rope passing over the pulley to lift the weight, it is exactly the
same as if you were standing overhead lifting the weight directly. It
is (in this case) 40 pounds either way. The weight of the object being
lifted using the first class pulley is not "split" into 20 lbs and 20
lbs. It is all one rope and all 40 lbs. The fact that you are using
the pulley merely changes the direction you have to pull. In some
cases this is more convenient, but the work and the weight is the
same.

To summarize:

The weight of the object is 40 lbs.
The weight on the rope is 40 lbs.
The weight on the hook is 40 lbs.
A first class pulley does not "split" the weight, nor does it give any
mechanical advantage. To raise the weight one foot, you pull the rope
one foot using 40 lbs of force.

If you were to attach the pulley to the weight, however, and tie the
rope overhead, and stand above the weight and pull on it, the lift
force on each side of the rope would be half the weight of the object
being lifted. You would have to pull with a force half as much as the
weight. In the example, the object weighing 40 lbs could be lifted
with a pull of 20 lbs of force. The other leg of the rope attached
overhead (above the weight) would be holding the other 20 lbs (the
ceiling holds 20 and you hold 20). You will have to pull the rope two
feet to raise the weight one foot. This is a 2:1 mechanical advantage.


If you add an additional pulley to the ceiling, you can now lift from
below, which is more comfortable. But you gain no additional
mechanical advantage beyond the 2:1 ratio.

However, if you add yet another pulley to the ceiling and run the rope
through it and then through the 3rd pulley (we now have one end of the
rope anchored, two ceiling pulleys, and one pulley on the weight) you
will then again halve the force needed to raise the pulley. Instead of
taking 20 lbs of force to raise a 40 lb weight, it now will take 10
pounds. Each segment of the rope now bears 1/4 of the weight but must
be pulled four feet to raise the weight one foot. The total weight on
the ceiling is still 40 lbs.

The problem everyone seems to be having is that there is no mechanical
advantage to using a first class pulley, so no force is shared. It is
the same as if you picked up the rope and lifted the weight directly
without using a pulley. There is only mechanical advantage -- shared
forces -- using the pulley attached to the weight, or using compound
pulleys such as in a block and tackle. Using the single pulley
attached to the ceiling, the force required is all on your side. The
weight cannot pick up or hold itself or half of itself -- or indeed
any of itself. The weight supported by the ceiling hook and pulley is
the full 40 lbs of the weight.

Here are some diagrams:

http://www.wcsscience.com/pulley/page.html

HTH.

If you guys had been paying attention in third grade instead of
throwing spitballs .... :-)

The same thing applies to a sailboat rigging. The more pulleys on the boom,
the more vertical lines and the less force you had to apply to hang on to
the main sheet. I has a small boat that had two pulleys, four vertical
lines on the main sheet. If there was only one pulley the force of the sail
would have pulled me right out of the boat.
MLD
"The Other Harry" wrote in message
...
[On Fri, 12 Mar 2004 19:36:49 GMT, "Michael Daly"
wrote:]

snip

Plug in different values of a for the angle of the line
running to the cleat and you'll see that the vertical
force on the top support only drops to equal the
weight of the load if the line running to the cleat
is horizontal. That also creates the maximum
horizontal load on the support.

Just so I understand this...

What I think you are saying (without trying to put words
in your mouth), is that if I want to reduce the tension on
the eye hook, the way to do that would be to hang the
cleat so that the angle of the line from the eye hook to
the cleat is above the horizontal. Less than 90 degrees.

If I place the cleat lower than 90 degrees, I will be
actually be increasing the load on the eye hook. The
closer to vertically down I get with the cleat, the more
the load on the hook will be. Up to double the original
weight of the pot.

Sound right?

Now then, what about the block & tackle gear between the
pot and the hook. Forget about the cleat for now.

Would it make any difference if there were more turns in
the line?

It's not that tough - I learned this stuff when I was 12.

Oh, hell no. It's just mind boggling.

--
Harry

"Harry K" wrote in message
om...

Wanna bet?
Greg

Yep except for my error on on labeling it 20lb vice 40.



Do yourself a favor and find a cheap fish scale, a weight, and a pulley, try
it yourself and get back with me!
Greg

"Harry K" wrote in message
om...

My confustion is trying to understand how, in the first experiment we
have 22lbs left, 22 lbs top and 22 (approx) right. Somehow it looks
like 22 lbs are magically appearing on the right. No, the strain on
the hook is not 44 lbs altho it would be if I were to han 22 lbs on
the right to balance the load.

Harry K

I think you need a differantc scale! The accuracy of the one you have is
very questionable!!
Greg

Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
\ /
40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

In article , (Harry K) wrote:
(Doug Miller) wrote in message
gy.com...
In article ,
(Harry K) wrote:
"Greg O" wrote in message
...
"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a hook
or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

It appears that *you* are the confused one here. A *movable* pulley will cut
the lifting force in half. A *fixed* pulley only changes the direction in
which the force is applied -- and this situation is entirely analogous to a
fixed pulley.

--------40----top-------------
/\
/ \
20/ \20
/ \
load/40 \anchor
------------bottom-------

Nope. You have a major problem he on the left side, a 40-lb weight is
suspended on a rope that has only 20 lbs tension. Doesn't work that way.

Suppose the anchor on the right is replaced by an un-anchored weight. What
weight is required on the right to balance the 40 lb weight on the left?
According to your diagram, the answer is 20 lbs. Now do you see your error?

--------------------top--------------
\anchor /anchor or pulley
\ /
\20 /20
\ /
\ /
\/
40
load with pulley
--------------------bottom----------

Not the same situation.

No. My first diagram is wrong in that the 20lbs should be 40. The
second is correct. Or am I misunderstanding your second part?

Permit me to clarify. I agree that your second diagram is correct. My point is
that it's not the same situation as the first diagram, and thus the loads
in the second diagram *must* be different from the loads in the first. You now
state correctly that the loads in the first diagram should be indicated as 40,
not 20, and I wish to emphasize that this is loadS plural, i.e. in both
segments of the rope -- thus the load on the top anchor in the first diagram
is in fact 80 pounds, not 40 as you stated in your text.

"Harry K" wrote in message
om...
"Greg O" wrote in message
...
Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
\ /
40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

No they are not the same: If the load in No.1 is 40 the drawing is
correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
with load 20 the pull on the top will be 20 not 40.
See my experiment that I used to confirm the theory. It confirms what
I just said.

Harry K

Harry, print out the page, flip it over, then explain why they are
differant!
Greg

In article , (Harry K) wrote:
"Greg O" wrote in message
...
Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
\ /
40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

No they are not the same: If the load in No.1 is 40 the drawing is
correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
with load 20 the pull on the top will be 20 not 40.

Absolute nonsense. In No. 2, there are *two* 20-pound loads. Do you maintain
that the anchor at the top supports only *one* of them?

See my experiment that I used to confirm the theory. It confirms what
I just said.

Your experiment confirms nothing except your own inability to take accurate
measurements. Your numbers were all over the map.
Harry K

In article , (Harry K) wrote:
(Doug Miller) wrote in message
. com...
In article ,
(Harry K) wrote:
(Doug Miller) wrote in message
gy.com...
In article ,
(Harry K) wrote:
"Greg O" wrote in message
...
"The Other Harry" wrote in message
...

The question was (and is), what happens to the load?

If the entire pot arrangement weighs 40 pounds, does half
of that load go to the top hook and half of it go to the
anchor hook?

--
Harry

I am assuming you have a rope attached to the pot, that runs up to a
hook
or
pulley attached to the ceiling,, then back down to an cleat.
If the pot weighs 40 lbs, the top hook in the ceiling, (or window
frame,
whatever!) with the pulley will be carrying 80 lbs. The tension,
(weight)
felt by the rope at the cleat will be 40 lbs.
Greg

Wrong. The tension on both sides will be equal (20 lbs) and the top
hook will feel 40lbs. There is nothing being added to the 40 lbs to
increase it to 80. I think you have confused the effect of a pulley
which, when rigged right, will cut the lifting force by 1/2.

It appears that *you* are the confused one here. A *movable* pulley will
cut
the lifting force in half. A *fixed* pulley only changes the direction in
which the force is applied -- and this situation is entirely analogous to
a
fixed pulley.

--------40----top-------------
/\
/ \
20/ \20
/ \
load/40 \anchor
------------bottom-------

Nope. You have a major problem he on the left side, a 40-lb weight is
suspended on a rope that has only 20 lbs tension. Doesn't work that way.

Suppose the anchor on the right is replaced by an un-anchored weight. What

weight is required on the right to balance the 40 lb weight on the left?
According to your diagram, the answer is 20 lbs. Now do you see your
error?

--------------------top--------------
\anchor /anchor or pulley
\ /
\20 /20
\ /
\ /
\/
40
load with pulley
--------------------bottom----------

Not the same situation.

No. My first diagram is wrong in that the 20lbs should be 40. The
second is correct. Or am I misunderstanding your second part?

Permit me to clarify. I agree that your second diagram is correct. My point
is
that it's not the same situation as the first diagram, and thus the loads
in the second diagram *must* be different from the loads in the first. You
now
state correctly that the loads in the first diagram should be indicated as
40,
not 20, and I wish to emphasize that this is loadS plural, i.e. in both
segments of the rope -- thus the load on the top anchor in the first diagram
is in fact 80 pounds, not 40 as you stated in your text.

No, it is 40. The second 40 is sort of a ghost 40lbs as it is the
-same- 40 lbs only extended to a second anchor.

Wrong.

Try it, lift 40 lbs
directly and then run the rope over a plley and pull on it, you will
still only see 40 lbs. See me exlanation to Greg O.

I *did* try it, as I described in an earlier post. Go back to the original
post in this thread. The question is how much load is placed on the beam or
whatever that the pulley hangs from. With a weight hanging free on one side,
and the rope it hangs from tied off to a stationary object on the other side,
the load placed on the pulley's support is approximately double that of the
weight, depending on the angle of the anchored segment of the rope. The
mathematics behind this has been clearly (and correctly) described by others
in this thread, and I won't repeat it here. You can look it up if you want to
understand why this doesn't work the way you think it does.

Your explanation to Greg is just as flawed as your explanation here.

Harry K

On 14 Mar 2004 10:24:11 -0800, (Harry K)
wrote:

| (Harry K) wrote in message . com...
| "Greg O" wrote in message ...
| Harry,
| Is this drawing, really any differant from
|
| 20 20
| \ /
| \ /
| \ /
| \ /
| \ /
| 40
|
| this one?
|
|
| 40
| / \
| / \
| / \
| / \
| / \
| / \
| 20 20
|
| Greg
|
| No they are not the same: If the load in No.1 is 40 the drawing is
| correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
| with load 20 the pull on the top will be 20 not 40.
| See my experiment that I used to confirm the theory. It confirms what
| I just said.
|
| Harry K
|
|
| A better explanation.
|
| Diagram 2 is a class 1 pulley. It only changes the direction of pull
| and does nothing to change the strain. If you were to tie off the
| left line at the top (hook) what will the strain on the hook be?
| Answer: 20 lbs, not 40. The 20lbs you are showing on the right leg is
| only the same 20 lbs extended to a different anchor, not an additonal
| 20 lbs.
|
| Diagram 1 is a class 2 pulley. It halves the load between two lines
| but requires, say, 10ft of rope pull to lift the load 5 ft.
|
| Harry K

Harry, you are absolutely and irrefutably correct. It's the difference
between two types of pulleys, one a simple pulley (the one fastened to
the ceiling) and one a moveable pulley (fastened to the weight, with
the rope tied to the ceiling on one side). It makes all the
difference.

By the way, these are principles known for thousands of years. The
pyramids were built using these simple machines and others. Leonardo
da Vinci commented on these pulleys. It's not opinion. There's nothing
to argue about. You don't even have to prove it with geometry -- as
Yogi Bera once said, "you could look it up."

On 14 Mar 2004 10:33:26 -0800, (Harry K)
wrote:

| (Doug Miller) wrote in message . com...
| In article , (Harry K) wrote:
| (Doug Miller) wrote in message
| gy.com...
| In article ,
| (Harry K) wrote:
| "Greg O" wrote in message
| ...
| "The Other Harry" wrote in message
| ...
|
| The question was (and is), what happens to the load?
|
| If the entire pot arrangement weighs 40 pounds, does half
| of that load go to the top hook and half of it go to the
| anchor hook?
|
| --
| Harry
|
| I am assuming you have a rope attached to the pot, that runs up to a hook
| or
| pulley attached to the ceiling,, then back down to an cleat.
| If the pot weighs 40 lbs, the top hook in the ceiling, (or window frame,
| whatever!) with the pulley will be carrying 80 lbs. The tension, (weight)
| felt by the rope at the cleat will be 40 lbs.
| Greg
|
| Wrong. The tension on both sides will be equal (20 lbs) and the top
| hook will feel 40lbs. There is nothing being added to the 40 lbs to
| increase it to 80. I think you have confused the effect of a pulley
| which, when rigged right, will cut the lifting force by 1/2.
|
| It appears that *you* are the confused one here. A *movable* pulley will cut
| the lifting force in half. A *fixed* pulley only changes the direction in
| which the force is applied -- and this situation is entirely analogous to a
| fixed pulley.
|
| --------40----top-------------
| /\
| / \
| 20/ \20
| / \
| load/40 \anchor
| ------------bottom-------
|
| Nope. You have a major problem he on the left side, a 40-lb weight is
| suspended on a rope that has only 20 lbs tension. Doesn't work that way.
|
| Suppose the anchor on the right is replaced by an un-anchored weight. What
| weight is required on the right to balance the 40 lb weight on the left?
| According to your diagram, the answer is 20 lbs. Now do you see your error?
|
| --------------------top--------------
| \anchor /anchor or pulley
| \ /
| \20 /20
| \ /
| \ /
| \/
| 40
| load with pulley
| --------------------bottom----------
|
| Not the same situation.
|
| No. My first diagram is wrong in that the 20lbs should be 40. The
| second is correct. Or am I misunderstanding your second part?
|
| Permit me to clarify. I agree that your second diagram is correct. My point is
| that it's not the same situation as the first diagram, and thus the loads
| in the second diagram *must* be different from the loads in the first. You now
| state correctly that the loads in the first diagram should be indicated as 40,
| not 20, and I wish to emphasize that this is loadS plural, i.e. in both
| segments of the rope -- thus the load on the top anchor in the first diagram
| is in fact 80 pounds, not 40 as you stated in your text.
|
| No, it is 40. The second 40 is sort of a ghost 40lbs as it is the
| -same- 40 lbs only extended to a second anchor. Try it, lift 40 lbs
| directly and then run the rope over a plley and pull on it, you will
| still only see 40 lbs. See me exlanation to Greg O.
|
| Harry K

The way to understand it better is to know that it is not a "ghost"
forty pounds, or an additional forty pounds, but rather the SAME forty
pounds.

"Harry K" wrote in message
m...
(Harry K) wrote in message
. com...
"Greg O" wrote in message
...
Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
\ /
40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

No they are not the same: If the load in No.1 is 40 the drawing is
correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
with load 20 the pull on the top will be 20 not 40.
See my experiment that I used to confirm the theory. It confirms what
I just said.

Harry K


A better explanation.

Diagram 2 is a class 1 pulley. It only changes the direction of pull
and does nothing to change the strain. If you were to tie off the
left line at the top (hook) what will the strain on the hook be?
Answer: 20 lbs, not 40. The 20lbs you are showing on the right leg is
only the same 20 lbs extended to a different anchor, not an additonal
20 lbs.

Diagram 1 is a class 2 pulley. It halves the load between two lines
but requires, say, 10ft of rope pull to lift the load 5 ft.

Harry K

Harry, when it comes to the forces seen at the three differant points in the
two drawings it makes no differance! Even though the drawnings are inverted,
they are essentially the same as far as the forces are concerned. Class 1,
or class 2 pulley has really nothing to do with it!
Greg

In article , wrote:
On 14 Mar 2004 10:24:11 -0800, (Harry K)
wrote:

| (Harry K) wrote in message
. com...
| "Greg O" wrote in message
...
| Harry,
| Is this drawing, really any differant from
|
| 20 20
| \ /
| \ /
| \ /
| \ /
| \ /
| 40
|
| this one?
|
|
| 40
| / \
| / \
| / \
| / \
| / \
| / \
| 20 20
|
| Greg
|
| No they are not the same: If the load in No.1 is 40 the drawing is
| correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
| with load 20 the pull on the top will be 20 not 40.
| See my experiment that I used to confirm the theory. It confirms what
| I just said.
|
| Harry K
|
|
| A better explanation.
|
| Diagram 2 is a class 1 pulley. It only changes the direction of pull
| and does nothing to change the strain. If you were to tie off the
| left line at the top (hook) what will the strain on the hook be?
| Answer: 20 lbs, not 40. The 20lbs you are showing on the right leg is
| only the same 20 lbs extended to a different anchor, not an additonal
| 20 lbs.
|
| Diagram 1 is a class 2 pulley. It halves the load between two lines
| but requires, say, 10ft of rope pull to lift the load 5 ft.
|
| Harry K

Harry, you are absolutely and irrefutably correct. It's the difference
between two types of pulleys, one a simple pulley (the one fastened to
the ceiling) and one a moveable pulley (fastened to the weight, with
the rope tied to the ceiling on one side). It makes all the
difference.

*IF* we were discussing moveable pulleys, yes -- but we're not, and that
appears to be the source of confusion for both of you. Go back to the original
post in this thread, and find out what the discussion is all about. Then read
some of the followups, particularly those from Michael Daly, to find out
exactly why Harry is absolutely and irrefutably INcorrect.

By the way, these are principles known for thousands of years. The
pyramids were built using these simple machines and others. Leonardo
da Vinci commented on these pulleys. It's not opinion. There's nothing
to argue about. You don't even have to prove it with geometry -- as
Yogi Bera once said, "you could look it up."

Yes, you could. You could start by looking up the initial post in this thread.

Wouldn't the force in the rope be applied to the load on the other end of
the rope?

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"Michael Daly" wrote in message
...
On 11-Mar-2004, "Stormin Mormon" wrote:

Hey, mike, you're confusing the issue! If you have 500 pounds hanging on a
block and tackle, it doesn't matter how many ropes, the screwhook at top
is
still holding 500 pounds (and now I'm confusing the issue).

Nope!

It's holding 500lb _plus_ the force in the rope.

Mike

Y'know, that sure sounds reasonable. I don't have a fisherman's spring
scale, but your answer sure sounds reasonable.

--

Christopher A. Young
Learn more about Jesus
www.lds.org
www.mormons.com


"Greg O" wrote in message
...

"Stormin Mormon" wrote in message
...
Hey, mike, you're confusing the issue! If you have 500 pounds hanging on a
block and tackle, it doesn't matter how many ropes, the screwhook at top
is
still holding 500 pounds (and now I'm confusing the issue).

--


Stormy, you have proven again, without a doubt that you do not know what you
are talking about!
In a situation I described, the hook in the ceiling will feel 2 times the
weight of the flower pot. If you use a more complex block and tackle, one
with several pulleys top and bottem, the more wraps and pulleys you use the
lower the load on the hook in the ceiling, but it will never be less than
the weight of the flower pot, plus the weight of the block and tackle and
the force needed on the rope to suspend the object.

The only way to have less load on the hook than the object weighs is to use
a pulley and the flower pot, and two hooks on the ceiling. then each hook
will hold 1/2 the weight.

If anyone fails to understand this, do as another poster did and get a fish
scale, a pulley, a weight, and a pice of rope, and try it your self!

Think of ot this way, the pot weighs 40 lbs. If you had a pot hanging on a
length of rope hooked to the ceiling, the rope, hook and all feel a load of
40 lbs. If you add pulley at the ceiling and run the rope over it and back
down, you need to apply a force of 40 lbs to suspend the pot, any more or
less force applied and the pot will go up or down. Now you have TWO 40 lb
loads, the pot, and the force to ballance the weight of the pot, which will
be equal. In this case 40 lbs X 2 = 80 lbs.

Another way is to think of this whole rope and flower pot situation as a
tetter-totter. You have a 40 lb kid on one side, so you need a 40 lb kid on
the other side to balance it. The weight the fulcrum of the tetter-totter
feels is 80 lbs. Asssuming the tetter-totter weighs nothing.

One 40 lb kid is the flower pot, the other 40 lb kid is the force on other
end of the rope needed to suspend the pot, and the fulcrum is the pulley or
hook.

Tomorrow night we will discuss complex block and tackles, test at 10 PM!!
;-)
Greg

"Harry K" wrote in message
m...

Ok. mentally tie the rope to the top anchor. What is the pull? Answer
20 lbs. Do you agree with that?

Now extend the rope to the bottom and tie it. What has changed?
Nothing.

Of course if you are adamant that 20 lbs just magically appear you
could go down to the school and ask the physics teacher. He will
probably show you the identical experiment with identical (altho more
acccurate) results I did.

Waiting your comment.

Harry K


Sure you are right if you are talking about this,

20
|
|
20
But we have been talking about this,

40
/\
/ \
/ \
20 20

Two totally differant deals!
With a load supportted by a rope that goes through a pulley shown imediately
above, there needs to be a equal force on the opisite end of the rope to
balance the load. The addition of the load used to balance the weight adds a
the additional load at the pulley.
Greg

"Harry K" wrote in message
om...

Well I have attempted to explain it as simply as I can. I repeat that
the one drawing is incorrect. do your own experiment, ask a physics
teacher or as Tom says, look it up.

Harry K

I have, and have come up with answers that oppose yours!
I helped a friend build a two post automotive lift using heavy chains and
hydraulic cylinders. It will lift 10,000+ lbs. We used princibles that we
have been discussing .
Greg

"Harry K" wrote in message
om...
This is for Greg O and Doug Miller;

40
I
I
I
I
I
I
I
40

That is what you have without the second extension to the bottom
anchor. Now metally run a line from the top to a second anchor. Have
you added anything?

Simple experiment to prove it without a scale:

Bucket with 20 or more lbs weight.
line.

Tie line to bucket and lift.

Now step on the loose end of line and pull the slack out with your
other hand.
Has the weight changed in your hand holding the bucket?

Harry K

You lost me here!!!
I don't unsderstand what slack you are refering to.
Your drawing is correct though, but what we have been discussing is
differant.
Greg
Greg

In article , (Harry K) wrote:
(Doug Miller) wrote in message
om...
In article ,
(Harry K) wrote:
"Greg O" wrote in message
...
Harry,
Is this drawing, really any differant from

20 20
\ /
\ /
\ /
\ /
\ /
40

this one?


40
/ \
/ \
/ \
/ \
/ \
/ \
20 20

Greg

No they are not the same: If the load in No.1 is 40 the drawing is
correct. If the load in No.2 is 20 the drawing is incorrect. In no.2
with load 20 the pull on the top will be 20 not 40.

Absolute nonsense. In No. 2, there are *two* 20-pound loads. Do you maintain
that the anchor at the top supports only *one* of them?

See my experiment that I used to confirm the theory. It confirms what
I just said.

Your experiment confirms nothing except your own inability to take accurate
measurements. Your numbers were all over the map.
Harry K

Try reading my experiment again. They conform to the theory within
accuracy limits of my tools. I don't follow the 'all over the map'
bit unless they just don't fit your (incorrect) preconcieved notions.

You obviously haven't read my first post in this thread, in which I stated
explicitly that my preconceived notion was the same as yours, and I found that
the experiment proved me _wrong_. You, on the other hand, drew conclusions
that _reinforced_ your preconceived notions, from data that don't begin to
justify them.

Ok. mentally tie the rope to the top anchor. What is the pull? Answer
20 lbs. Do you agree with that?

Assuming that a 20-lb weight is suspended, sure.

Now extend the rope to the bottom and tie it. What has changed?
Nothing.

Agreed.

Now untie the rope from the top anchor. The load on that anchor *does* become
40 lbs.

Of course if you are adamant that 20 lbs just magically appear you
could go down to the school and ask the physics teacher. He will
probably show you the identical experiment with identical (altho more
acccurate) results I did.

You got one thing right, anyway: your experimental results were not accurate.