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Pulling the rope with one hand is as heavy as with two hands?
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$begingroup$
There is this box, having two holes, and the ropes going through each of them.
I try to pull the left rope with my left hand... And it's heavy...
Then I try to pull the right rope with my right hand... It's also heavy, as heavy as before.
Ok so... I think both ropes are directly connected to a single weight.
So I try to pull both ropes with my both hands, hoping to reduce the force exerted by each arm by $50%$...
But... I'm wrong... The box is no easier to lift with two arms!
Ah, of course. There are two weights. Each rope is connected to different weight...
Yes, that makes sense!
Let's open this box to prove that I'm right.
...
Wait... What?! There is only one weight there?! Wow, what an amazing contraption!
So, do you know how can this be happening?
physics
edited 13 hours ago
Nuclear Wang
1,472617
asked 18 hours ago
athinathin
8,98922981
$endgroup$
|
show 7 more comments
$begingroup$
There is this box, having two holes, and the ropes going through each of them.
I try to pull the left rope with my left hand... And it's heavy...
Then I try to pull the right rope with my right hand... It's also heavy, as heavy as before.
Ok so... I think both ropes are directly connected to a single weight.
So I try to pull both ropes with my both hands, hoping to reduce the force exerted by each arm by $50%$...
But... I'm wrong... The box is no easier to lift with two arms!
Ah, of course. There are two weights. Each rope is connected to different weight...
Yes, that makes sense!
Let's open this box to prove that I'm right.
...
Wait... What?! There is only one weight there?! Wow, what an amazing contraption!
So, do you know how can this be happening?
physics
edited 13 hours ago
Nuclear Wang
1,472617
asked 18 hours ago
athinathin
8,98922981
$endgroup$
2
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
$endgroup$
– Arnaud Mortier
18 hours ago
1
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
$endgroup$
– athin
18 hours ago
1
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
$endgroup$
– athin
18 hours ago
2
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago
|
show 7 more comments
$begingroup$
There is this box, having two holes, and the ropes going through each of them.
I try to pull the left rope with my left hand... And it's heavy...
Then I try to pull the right rope with my right hand... It's also heavy, as heavy as before.
Ok so... I think both ropes are directly connected to a single weight.
So I try to pull both ropes with my both hands, hoping to reduce the force exerted by each arm by $50%$...
But... I'm wrong... The box is no easier to lift with two arms!
Ah, of course. There are two weights. Each rope is connected to different weight...
Yes, that makes sense!
Let's open this box to prove that I'm right.
...
Wait... What?! There is only one weight there?! Wow, what an amazing contraption!
So, do you know how can this be happening?
physics
edited 13 hours ago
Nuclear Wang
1,472617
asked 18 hours ago
athinathin
8,98922981
$endgroup$
There is this box, having two holes, and the ropes going through each of them.
I try to pull the left rope with my left hand... And it's heavy...
Then I try to pull the right rope with my right hand... It's also heavy, as heavy as before.
Ok so... I think both ropes are directly connected to a single weight.
So I try to pull both ropes with my both hands, hoping to reduce the force exerted by each arm by $50%$...
But... I'm wrong... The box is no easier to lift with two arms!
Ah, of course. There are two weights. Each rope is connected to different weight...
Yes, that makes sense!
Let's open this box to prove that I'm right.
...
Wait... What?! There is only one weight there?! Wow, what an amazing contraption!
So, do you know how can this be happening?
physics
physics
edited 13 hours ago
Nuclear Wang
1,472617
asked 18 hours ago
athinathin
8,98922981
edited 13 hours ago
Nuclear Wang
1,472617
asked 18 hours ago
athinathin
8,98922981
edited 13 hours ago
Nuclear Wang
1,472617
edited 13 hours ago
Nuclear Wang
1,472617
edited 13 hours ago
Nuclear Wang
1,472617
1,472617
asked 18 hours ago
athinathin
8,98922981
asked 18 hours ago
athinathin
8,98922981
asked 18 hours ago
athinathin
8,98922981
8,98922981
2
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
$endgroup$
– Arnaud Mortier
18 hours ago
1
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
$endgroup$
– athin
18 hours ago
1
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
$endgroup$
– athin
18 hours ago
2
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago
|
show 7 more comments
2
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
$endgroup$
– Arnaud Mortier
18 hours ago
1
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
$endgroup$
– athin
18 hours ago
1
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
$endgroup$
– athin
18 hours ago
2
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago
2
2
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
$endgroup$
– Arnaud Mortier
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
$endgroup$
– Arnaud Mortier
18 hours ago
1
1
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
$endgroup$
– athin
18 hours ago
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
$endgroup$
– athin
18 hours ago
1
1
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
$endgroup$
– athin
18 hours ago
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
$endgroup$
– athin
18 hours ago
2
2
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago
|
show 7 more comments
6 Answers
6
active
oldest
votes
$begingroup$
The weight is attached to a pulley. The two ends are of the same rope that runs through the pulley. Also, the rope is tied to two ropes that connect it to the top of the box on either side of the pulley. When you pull one end of the rope, the pulley lets you cut the weight in half, but when you pull on both ends, you do not use the pulley and lift the entire weight.
Below is my attempt at depicting this contraption.
answered 18 hours ago
noednenoedne
9,87312769
$endgroup$
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
|
show 3 more comments
$begingroup$
Maybe the ropes are
attached to different ends of the thin weight, which is lying flat inside the box.
When you pull only one rope,
only that end of the weight rises. The centre of mass of the weight moves up by half the distance pulled, so the force required is half of the weight of the weight
And when you pull on both ropes
The whole weight rises, and the force is equally split between the two ropes.
In both cases, the force on any pulled rope is the same, namely
one half of the weight of the weight.
answered 17 hours ago
BassBass
31.7k475195
$endgroup$
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
|
show 1 more comment
$begingroup$
Possible answer
The ropes themselves are significantly heavier than the single weight so that when you lift with either with the left or right hand you're mostly lifting the rope on that side (together with small contributions from the weight and the end of the other rope). When you lift with both hands, you are lifting both ropes.
answered 17 hours ago
hexominohexomino
47.8k4143225
$endgroup$
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
add a comment |
$begingroup$
This explains it:
The box is sealed from outside and the ropes are not connected to the weight. When you pull the ropes out you are creating a pressure difference caused by the displacement of the volume occupied by the ropes (isochoric process). If the ropes are equal in size, this will mean that you will get the same displacement per rope, i.e. the same pressure difference per rope thus the same force per rope.
This is analogous to a case where you connect two syringes (instead of ropes) to a sealed box (optionally with something just laying inside it).
answered 17 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Maybe
There is a pulley hinged at the box ceiling. There is a single rope. The weight has two pulleys attached to it for the rope to pass through. Both ends of the rope are tied to a ceiling outside the box. The rope, from one side, enters the box, passes under the first pulley of the weight, over the hinged pulley, down under the second pulley attached to the weight and then out of the box all the way to the other tied end. When you pull either side of the rope (that appears as a separate rope), the mechanical advantage is 4 (thanks to Hans Janssen for correcting me here), thus reducing the effective weight by 4. When you pull at both sides, the hinged pulley's function is lost and you end up with the mechanical advantage of 2 for each hand. Consequently, the effective weight does not change.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
As an alternative to my previous answer, this would also work:
The ropes are independent but connected to the weight. But if the ropes are not under tension, and just rolled down on the base of box, when you pull the ropes up you would just feel the weight of the ropes, not the weight. Thus, pulling one, the other, or both, will mean that you will be just lifting independent (but identical) ropes out of the ground.
answered 15 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
add a comment |
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6 Answers
6
active
oldest
votes
6 Answers
6
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The weight is attached to a pulley. The two ends are of the same rope that runs through the pulley. Also, the rope is tied to two ropes that connect it to the top of the box on either side of the pulley. When you pull one end of the rope, the pulley lets you cut the weight in half, but when you pull on both ends, you do not use the pulley and lift the entire weight.
Below is my attempt at depicting this contraption.
answered 18 hours ago
noednenoedne
9,87312769
$endgroup$
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
|
show 3 more comments
$begingroup$
The weight is attached to a pulley. The two ends are of the same rope that runs through the pulley. Also, the rope is tied to two ropes that connect it to the top of the box on either side of the pulley. When you pull one end of the rope, the pulley lets you cut the weight in half, but when you pull on both ends, you do not use the pulley and lift the entire weight.
Below is my attempt at depicting this contraption.
answered 18 hours ago
noednenoedne
9,87312769
$endgroup$
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
|
show 3 more comments
$begingroup$
The weight is attached to a pulley. The two ends are of the same rope that runs through the pulley. Also, the rope is tied to two ropes that connect it to the top of the box on either side of the pulley. When you pull one end of the rope, the pulley lets you cut the weight in half, but when you pull on both ends, you do not use the pulley and lift the entire weight.
Below is my attempt at depicting this contraption.
answered 18 hours ago
noednenoedne
9,87312769
$endgroup$
The weight is attached to a pulley. The two ends are of the same rope that runs through the pulley. Also, the rope is tied to two ropes that connect it to the top of the box on either side of the pulley. When you pull one end of the rope, the pulley lets you cut the weight in half, but when you pull on both ends, you do not use the pulley and lift the entire weight.
Below is my attempt at depicting this contraption.
answered 18 hours ago
noednenoedne
9,87312769
edited 17 hours ago
answered 18 hours ago
noednenoedne
9,87312769
answered 18 hours ago
noednenoedne
9,87312769
answered 18 hours ago
noednenoedne
9,87312769
9,87312769
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
|
show 3 more comments
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
$begingroup$
My physics is quite rusty, so please let me know if this is mistaken.
$endgroup$
– noedne
18 hours ago
28
28
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
All hail the mighty man in the box, balancing a table on his long arms!
$endgroup$
– infinitezero
17 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
Why the two ropes to the top of the box? The other end of the rope (not being pulled) works just fine combined with the pulley.
$endgroup$
– Hans Janssen
15 hours ago
2
2
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
$begingroup$
@HansJanssen Or are you suggesting that when you pull one end of the rope, you are still holding the other end taut?
$endgroup$
– noedne
15 hours ago
1
1
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
$begingroup$
And yeah, actually this is the trick! ><
$endgroup$
– athin
14 hours ago
|
show 3 more comments
$begingroup$
Maybe the ropes are
attached to different ends of the thin weight, which is lying flat inside the box.
When you pull only one rope,
only that end of the weight rises. The centre of mass of the weight moves up by half the distance pulled, so the force required is half of the weight of the weight
And when you pull on both ropes
The whole weight rises, and the force is equally split between the two ropes.
In both cases, the force on any pulled rope is the same, namely
one half of the weight of the weight.
answered 17 hours ago
BassBass
31.7k475195
$endgroup$
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
|
show 1 more comment
$begingroup$
Maybe the ropes are
attached to different ends of the thin weight, which is lying flat inside the box.
When you pull only one rope,
only that end of the weight rises. The centre of mass of the weight moves up by half the distance pulled, so the force required is half of the weight of the weight
And when you pull on both ropes
The whole weight rises, and the force is equally split between the two ropes.
In both cases, the force on any pulled rope is the same, namely
one half of the weight of the weight.
answered 17 hours ago
BassBass
31.7k475195
$endgroup$
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
|
show 1 more comment
$begingroup$
Maybe the ropes are
attached to different ends of the thin weight, which is lying flat inside the box.
When you pull only one rope,
only that end of the weight rises. The centre of mass of the weight moves up by half the distance pulled, so the force required is half of the weight of the weight
And when you pull on both ropes
The whole weight rises, and the force is equally split between the two ropes.
In both cases, the force on any pulled rope is the same, namely
one half of the weight of the weight.
answered 17 hours ago
BassBass
31.7k475195
$endgroup$
Maybe the ropes are
attached to different ends of the thin weight, which is lying flat inside the box.
When you pull only one rope,
only that end of the weight rises. The centre of mass of the weight moves up by half the distance pulled, so the force required is half of the weight of the weight
And when you pull on both ropes
The whole weight rises, and the force is equally split between the two ropes.
In both cases, the force on any pulled rope is the same, namely
one half of the weight of the weight.
answered 17 hours ago
BassBass
31.7k475195
edited 17 hours ago
answered 17 hours ago
BassBass
31.7k475195
answered 17 hours ago
BassBass
31.7k475195
answered 17 hours ago
BassBass
31.7k475195
31.7k475195
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
|
show 1 more comment
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
$begingroup$
My physics is rusty, but I don't think the distance moved affects the forces.
$endgroup$
– noedne
17 hours ago
2
2
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
@noedne Sure it does. It all comes back to the law of the lever: gravity pulls down at the center of mass, and the rope pulls up at exactly twice the distance from the fulcrum, which we know from the fact that the rope moves twice as much as the center of gravity.
$endgroup$
– Bass
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
Thanks, I see it now.
$endgroup$
– noedne
17 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
$begingroup$
This is also a good (alternative) answer. I should mention that the weight is not thin, it's a large solid one.
$endgroup$
– athin
14 hours ago
1
1
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
$begingroup$
@Bass I think the pulley is needed for the situation to hold while lifting; the rod would work to balance the ropes at one specific height, but at any other height one of the ropes would be slack, so the weight would not be distributed.
$endgroup$
– noedne
13 hours ago
|
show 1 more comment
$begingroup$
Possible answer
The ropes themselves are significantly heavier than the single weight so that when you lift with either with the left or right hand you're mostly lifting the rope on that side (together with small contributions from the weight and the end of the other rope). When you lift with both hands, you are lifting both ropes.
answered 17 hours ago
hexominohexomino
47.8k4143225
$endgroup$
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
add a comment |
$begingroup$
Possible answer
The ropes themselves are significantly heavier than the single weight so that when you lift with either with the left or right hand you're mostly lifting the rope on that side (together with small contributions from the weight and the end of the other rope). When you lift with both hands, you are lifting both ropes.
answered 17 hours ago
hexominohexomino
47.8k4143225
$endgroup$
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
add a comment |
$begingroup$
Possible answer
The ropes themselves are significantly heavier than the single weight so that when you lift with either with the left or right hand you're mostly lifting the rope on that side (together with small contributions from the weight and the end of the other rope). When you lift with both hands, you are lifting both ropes.
answered 17 hours ago
hexominohexomino
47.8k4143225
$endgroup$
Possible answer
The ropes themselves are significantly heavier than the single weight so that when you lift with either with the left or right hand you're mostly lifting the rope on that side (together with small contributions from the weight and the end of the other rope). When you lift with both hands, you are lifting both ropes.
answered 17 hours ago
hexominohexomino
47.8k4143225
answered 17 hours ago
hexominohexomino
47.8k4143225
answered 17 hours ago
hexominohexomino
47.8k4143225
answered 17 hours ago
hexominohexomino
47.8k4143225
47.8k4143225
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
add a comment |
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
That only works if the weight would be 0 kg. If that would be the case it's not really called a weight right...
$endgroup$
– Hans Janssen
15 hours ago
2
2
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
@HansJanssen Maybe there's a weight in the box but not connected to the ropes?
$endgroup$
– SpoonMeiser
15 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
This is actually a good (alternative) answer. Sorry but I should say that the rope is a usual rope which is not heavy, and certainly, the weight should be much heavier than the rope.
$endgroup$
– athin
14 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
$begingroup$
@HansJanssen or there is simply not a weight. Just heavy ropes.
$endgroup$
– abligh
9 hours ago
add a comment |
$begingroup$
This explains it:
The box is sealed from outside and the ropes are not connected to the weight. When you pull the ropes out you are creating a pressure difference caused by the displacement of the volume occupied by the ropes (isochoric process). If the ropes are equal in size, this will mean that you will get the same displacement per rope, i.e. the same pressure difference per rope thus the same force per rope.
This is analogous to a case where you connect two syringes (instead of ropes) to a sealed box (optionally with something just laying inside it).
answered 17 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
This explains it:
The box is sealed from outside and the ropes are not connected to the weight. When you pull the ropes out you are creating a pressure difference caused by the displacement of the volume occupied by the ropes (isochoric process). If the ropes are equal in size, this will mean that you will get the same displacement per rope, i.e. the same pressure difference per rope thus the same force per rope.
This is analogous to a case where you connect two syringes (instead of ropes) to a sealed box (optionally with something just laying inside it).
answered 17 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
This explains it:
The box is sealed from outside and the ropes are not connected to the weight. When you pull the ropes out you are creating a pressure difference caused by the displacement of the volume occupied by the ropes (isochoric process). If the ropes are equal in size, this will mean that you will get the same displacement per rope, i.e. the same pressure difference per rope thus the same force per rope.
This is analogous to a case where you connect two syringes (instead of ropes) to a sealed box (optionally with something just laying inside it).
answered 17 hours ago
cinicocinico
1665
$endgroup$
This explains it:
The box is sealed from outside and the ropes are not connected to the weight. When you pull the ropes out you are creating a pressure difference caused by the displacement of the volume occupied by the ropes (isochoric process). If the ropes are equal in size, this will mean that you will get the same displacement per rope, i.e. the same pressure difference per rope thus the same force per rope.
This is analogous to a case where you connect two syringes (instead of ropes) to a sealed box (optionally with something just laying inside it).
answered 17 hours ago
cinicocinico
1665
edited 16 hours ago
answered 17 hours ago
cinicocinico
1665
answered 17 hours ago
cinicocinico
1665
answered 17 hours ago
cinicocinico
1665
1665
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
$begingroup$
Ah, this will work if the holes are small enough only for the rope, and no air can come from outside, cmiiw?
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Maybe
There is a pulley hinged at the box ceiling. There is a single rope. The weight has two pulleys attached to it for the rope to pass through. Both ends of the rope are tied to a ceiling outside the box. The rope, from one side, enters the box, passes under the first pulley of the weight, over the hinged pulley, down under the second pulley attached to the weight and then out of the box all the way to the other tied end. When you pull either side of the rope (that appears as a separate rope), the mechanical advantage is 4 (thanks to Hans Janssen for correcting me here), thus reducing the effective weight by 4. When you pull at both sides, the hinged pulley's function is lost and you end up with the mechanical advantage of 2 for each hand. Consequently, the effective weight does not change.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Maybe
There is a pulley hinged at the box ceiling. There is a single rope. The weight has two pulleys attached to it for the rope to pass through. Both ends of the rope are tied to a ceiling outside the box. The rope, from one side, enters the box, passes under the first pulley of the weight, over the hinged pulley, down under the second pulley attached to the weight and then out of the box all the way to the other tied end. When you pull either side of the rope (that appears as a separate rope), the mechanical advantage is 4 (thanks to Hans Janssen for correcting me here), thus reducing the effective weight by 4. When you pull at both sides, the hinged pulley's function is lost and you end up with the mechanical advantage of 2 for each hand. Consequently, the effective weight does not change.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Maybe
There is a pulley hinged at the box ceiling. There is a single rope. The weight has two pulleys attached to it for the rope to pass through. Both ends of the rope are tied to a ceiling outside the box. The rope, from one side, enters the box, passes under the first pulley of the weight, over the hinged pulley, down under the second pulley attached to the weight and then out of the box all the way to the other tied end. When you pull either side of the rope (that appears as a separate rope), the mechanical advantage is 4 (thanks to Hans Janssen for correcting me here), thus reducing the effective weight by 4. When you pull at both sides, the hinged pulley's function is lost and you end up with the mechanical advantage of 2 for each hand. Consequently, the effective weight does not change.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
Maybe
There is a pulley hinged at the box ceiling. There is a single rope. The weight has two pulleys attached to it for the rope to pass through. Both ends of the rope are tied to a ceiling outside the box. The rope, from one side, enters the box, passes under the first pulley of the weight, over the hinged pulley, down under the second pulley attached to the weight and then out of the box all the way to the other tied end. When you pull either side of the rope (that appears as a separate rope), the mechanical advantage is 4 (thanks to Hans Janssen for correcting me here), thus reducing the effective weight by 4. When you pull at both sides, the hinged pulley's function is lost and you end up with the mechanical advantage of 2 for each hand. Consequently, the effective weight does not change.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 14 hours ago
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
answered 15 hours ago
Mazurka FahrMazurka Fahr
514
514
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Mazurka Fahr is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
add a comment |
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
1
1
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
Actually, with that design the mechanical advantage when pulling one rope is 4, and it is 2 when pulling both ropes. Still solves the puzzle tough ;)
$endgroup$
– Hans Janssen
15 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
@Hans Janssen. Corrected it. Thanks!
$endgroup$
– Mazurka Fahr
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
$begingroup$
Yep, this is also how to solve the puzzle with pulley trick. Sadly @noedne is faster here ><
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
As an alternative to my previous answer, this would also work:
The ropes are independent but connected to the weight. But if the ropes are not under tension, and just rolled down on the base of box, when you pull the ropes up you would just feel the weight of the ropes, not the weight. Thus, pulling one, the other, or both, will mean that you will be just lifting independent (but identical) ropes out of the ground.
answered 15 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
As an alternative to my previous answer, this would also work:
The ropes are independent but connected to the weight. But if the ropes are not under tension, and just rolled down on the base of box, when you pull the ropes up you would just feel the weight of the ropes, not the weight. Thus, pulling one, the other, or both, will mean that you will be just lifting independent (but identical) ropes out of the ground.
answered 15 hours ago
cinicocinico
1665
$endgroup$
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
As an alternative to my previous answer, this would also work:
The ropes are independent but connected to the weight. But if the ropes are not under tension, and just rolled down on the base of box, when you pull the ropes up you would just feel the weight of the ropes, not the weight. Thus, pulling one, the other, or both, will mean that you will be just lifting independent (but identical) ropes out of the ground.
answered 15 hours ago
cinicocinico
1665
$endgroup$
As an alternative to my previous answer, this would also work:
The ropes are independent but connected to the weight. But if the ropes are not under tension, and just rolled down on the base of box, when you pull the ropes up you would just feel the weight of the ropes, not the weight. Thus, pulling one, the other, or both, will mean that you will be just lifting independent (but identical) ropes out of the ground.
answered 15 hours ago
cinicocinico
1665
answered 15 hours ago
cinicocinico
1665
answered 15 hours ago
cinicocinico
1665
answered 15 hours ago
cinicocinico
1665
1665
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
add a comment |
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
$begingroup$
Ah, I should mention that the rope can be pulled, means it's not stuck to the base or any kinds of stuff which make it unable to move.
$endgroup$
– athin
14 hours ago
add a comment |
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2
$begingroup$
Is this unexpected?
$endgroup$
– noedne
18 hours ago
$begingroup$
Do you measure how hard it is to lift the weight or to keep it in a high position, or both?
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– Arnaud Mortier
18 hours ago
1
$begingroup$
@noedne Given the final contraption, it's expected to behave as the story.
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– athin
18 hours ago
1
$begingroup$
@ArnaudMortier The measurement can be exact. Say, you need $x$ Newton to perform those $3$ pullings. (Well, for the third one, it should be $2x$ Newton in total as using both of hands $= x + x$.)
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– athin
18 hours ago
2
$begingroup$
@athin OK, so what's actually happening is that the box weighs twice as much (not the same amount) when pulling both ropes compared to when pulling with either rope individually. Because the weight of the box doubles when using both arms, the force exerted by a single arm is identical in all 3 cases (left arm, right arm, both arms).
$endgroup$
– Nuclear Wang
13 hours ago