String Theory in Everyday Life?

Can't tell unless the volume of the bucket is known,

assuming the bucket would weigh more than 5kg when full:

If you fill the bucket slowly the string at the top will break first due to the inertia over coming the 5kg weight.

If you fill it fast it will break between the bucket and the weight.

Just a guess, i think i saw this in Physics 101.

Yep, after I posted i reread it slowly and saw the "slowly" part so yes it would be the top one.

this answer gets my vote. (GA) The top one has the 5kg PLUS the weight of the lower stuff.

To bad it was incorrect :)

Is it an ordinary string or a superstring?

The top string breaks first. Its tension exceeds the tension in the lower string by the weight of a 5 kg mass, or about 49 Newtons.

Assuming the 5kg string break strenght is accurate without a safety factor, you will never get the bucket to the required test 5kg weight. The first string will break immediately.

The top of course. It has the full weight of the 5kg weight and the bucket.

You must explain why, there is a reason as it could break below also.

What kind of knot? The string will likely break at the knot. If two different knots are used this could influence which one breaks first.

You are thinking too much.

In explaining this situation, too much is left to our imagination. The sentencce "and tie a bucket beneath the 5 kg weight" does not make clear where the loads are imposed. Some readers have presumed one way; ambiguity remains, which misled an early responder. If the two strings are in parallel from the hitching post to the weight, then loads are quite different from the situation where the bucket's string is tied to the weight.

You are putting too much thought into it, it is a classic physics 101 question. Make an assumption with a solution.

W R O N G ! ! ! Lots depends on lots of additional factors! Was the string made in China or New Hampshire? What kind of quality assurance is there along each of the 2 lengths used (as well as the knots!)?

Was the 1st length (down to the 5kg weight) only 2 feet, and the 2nd length 20 ft (the OP said "nice and high")...?!?!

No wonder I'm going insane! When I first visited CR4, good solid advice was routinely given... NOW, all the insane 'homework' questions, over-unity claims, "How to turn my washing machine motor into an efficient generator" questions and-the-like seem to be rubbing-off-on ... and dumbing-down everyone!

H.M.L.

[ "PS" ~ any chance that CR4 will EVER allow 'moderators' to perform Grammer-&-Spelling edits to some of the posts...? How irritating, to try and make sense of some of the "late-night-half-drunk" posts...]

Why do i have to keep posting!! it is solved!! (prev as guest)

You dummy, think out side of the box. IT'S A PHYSICS PROBLEM AND IN INVOLVES MAKING ASSUMPTIONS DUE TO LIMITED INFO!

As one before said it is a static system, filling slowly will allow the inertia of the water weight to Overcome the static weight of the 5kg. If it was filled fast it would not have the time and would break below the 5kg.

If the user had given more info such as: the type of string, diameter, lengths, volume of the bucket etc... then you could solve it that way possibly.

The clue to the answer was given "filled slowly"

IT'S ONE OF NEWTONS LAW!

If you fill the bucket slowly, the tension in the bottom string is simply the weight of the bucket + water, while the tension in the top string is bucket + water + 5kg. The top string will break first. When you quickly fill the bucket + water, the tension in the bottom string becomes very large while the tension of the top string remains ~5kg since the mass does not accelerate. The bottom string breaks.

There you have it!

play nice boys... so CR4 remains a fun place for everyone. nobody wants to listen to slander.

Sorry I meant "you dummy" as in Sanford & Son, ya know like "you big dummy! :)

But, given perfect circumstances. i.e. ignoring knots, inconsistencies in the string etc. : is it possible to create a theoretical scenario in which the second (top) string does not break shortly after the first (bottom).

Humm, well.. it would violate Newton's 1st law. We need a physics phd to comment on this one.

I have read about where both strings have broken at the same time but the naked eye cannot see what a properly instrumented experiment could provide.

A little more clarification...

Inertia is the resistance of mass, i.e. any physical object, to a change in its state of motion.

It is Newton's 1st law.

The reason it breaks above the weight:

if filled slowly the weight of the water has time to transfer PAST the 5kg and therefore It will be the weight of water in the bucket + the 5kg.

If filled fast it would be a jerk motion and the weight of the water will not have time to overcome the inertia of the 5kg weight causing it to break below the 5kg.

Re: "it is solved!!"... (excuse me, but... "You Dummy!")

As Post 34 states: "If the bottom string is really, really long, then it more often breaks first. I don't know why that happens."

My dad taught me how I could break a LONG pencil between three fingers VERY easily, but would hurt myself trying to perform the exact same thing on a very SHORT pencil. LIKEWISE, he showed me how it would cut into my skin trying to break a short length of string wrapped-around two fingers of each hand; but, we could tie a 20-ft length to the stair post, and (wrapped around 2 fingers, again), I could then break it with a good tug!

S O M E things are, in fact, pretty simple ... cut-and-dried.

Many other things are a bit more complicated. Difficult-to-swallow, even. Might even require "ditching" a few preconceived ideas or biases in order to fully understand.

Help me Lord, to better understand ALL "the facts", as only You can teach....

After I filtered out the typos, I see that you have correctly analyzed one possible situation.... the most popular one in these postings.

The situation where the second string is attached between the upper hitching post and the bucket, and is longer than the first string, meets all the conditions of the original posting, and has not been recognized or analyzed by most of us. In that case, the effect of the water is minimal on the first string, and the second will assuredly break first.

In the situation where the tensile strength of the string is less than 5 Kgf, the first string will break first. In that case, the second string, attached to the upper hitching post, will break when the weight of the bucket + water exceeds said tensile strength.

If a problem has ambiguity, one must then analyze all the possibilities ... not just the first one upon which your brain focusses.

A well-defined question has one answer. In real life, we are seldom presented with such well-defined questions.

In answer to the "too much thinking" comment above: No. Just the right amount of thinking.

The problem has nothing to do with tensile strength.

There is no mention of the string lengths in the original post.

it is Newtons first law, a high school physics 101 test problem.

It is the only answer for what was given, there would be no reason to look at other options unless a new scenario was presented.

And i don't mind typo's, they keep me humble:)

"The problem has nothing to do with tensile strength."

unless of course it is 60# test, and the strings never break!

I meant to say There is no mention of the string lengths in the "THIS" post.

Does the problem have ambiguity? The OP asks:

Which string breaks first?

• The top one.
• The bottom one.
• Impossible to tell.

If the second string is attached to the upper hitching post, the designation "top one" and "bottom one" has no meaning.

But, from the OP's wording, you could have another scenario where you "tie a bucket beneath the 5 kg weight" (kg is a unit of mass, not weight). You tie one end of the string to the bucket and don't tie the other end to anything. Now you fill the bucket with water until a string breaks. Which string breaks first? The top one, because it is the only string which is loaded.

Maybe it would have been better to state that a bucket is suspended from the 5 kg mass with a length of string from the same spool.

I get your point, but it was a "challenge" question so in my opinion one has to read between the lines to extract the givens and base your result on an assumption that one comes up with.

in this case the first clues that i saw were:

1. slowly

2. 5kg, which is a mass. Whenever i see "mass" I think Newton.

It was clear to me that there were 2 pieces of string, a 5kg weight (mass), a bucket, and at some point water.

it was not so clear that the string was tied to a physical object OR was the 5kg mass tied tightly to the up high physical object NOT dangling. This could have been a bit more clear in the post.

I see it in this order: string tied to a high object, then attach a 5kg mass, then more string, then the bucket.

I saw it that way because I have seen it n high school and college physics, Statics classes in one form or another. It is a classic lab on Newton's first law.

Could it there be a different solution? sure! But you have to list your assumptions and solve for it, Their were more than a few time where i didn't know the answer to a particular problem on a test in physic's so i based my answer on stated assumptions that i pulled out of the air and was given credit and once or twice extra credit for the solution.

mk

Since I've seen any number of good answers, I should perhaps give the "rest of the story" as Paul Harvey used to say. The student who asked has so far refused to actually try this, preferring instead to argue about what should happen. The reason to actually do the experiment is shown by the numerous good answers on here, answers which covered all three possibilities. To wit,

BTW, I really did mean to tie the bucket directly onto the bottom of the 5 kg weight. I know kg is mass, but it's common usage weight in the US (What about in Europe?).

Depending on how I rigged this experiment, I got all three answers.

The use of "crushing" knots almost always made the string break at a knot. The type of knot makes a difference since you can change the amount of crushing.

The top string is clearly in the greatest tension since it stretches more. Failure is usually related to that tension, but cannot always be correctly predicted. I used French made string for most of the experiments and it is terrifically consistent.

Bouncing the bottom bucket usually breaks the top string (if you've taken care of the knots) even though the classic Physics puzzle says otherwise. I don't know why this is so.

If the knots are taken care of, and good string is used, the top string usually breaks first. This is maybe 90% true - I did fewer than twenty trials, so can't say much about percentage.

If the bottom string breaks first, the elastically stretched top string rebounds, picking up the 5 kg weight which then drops and breaks the top string also.

If the bottom string is really, really long, then it more often breaks first. I don't know why that happens.

There are some pretty smart folks on here! I wish I could get the student I mentioned to see that and do some experimentation.

If the bottom string is really, really long, then it more often breaks first. I don't know why that happens.

However good the string is it is not consistent throughout its length: you're more likely to get a weak section in a really long length.

That's a real possibility. I'm not sure yet how to test for that (without investing 12-15 hours). Any ideas?

Any ideas?

No. You'd just have to do a statistical analysis of the breaking point of lots of bits of string.

How long is a piece of string?

After reading some of the responses, it occurs to me that no one questioned using "a string" to hold a 5 Kg weight plus a bucket being filled (with water?). I think a "cord" at minimum or a thin rope would be required. The string used for flying a kite, for example, would likely have a lower breaking strength than supporting a 5 Kg weight + a bucket + weight in the bucket. Semantics?

Semantix. I believe the term "string" includes those cords with 5 to 10 Kg ultimate tensile strengths. As I said above, a big paragraph of definitions would narrow the field of correct answers. It would also have obviated all this fun discussion.

Friday night. 3 ropes are done a hard week's work on the ranch; they head into town for fun. They go into the first tavern, but are thrown out for being ropes. One has a good idea. He twists himself up and gets all fluffy and loose.... goes into the next tavern. He gets seated. The waitress then says: " Are you a rope? We don't serve your kind here!" to which he replies: " Nope. 'fraid not..."

Semantics,it is a physics 101 question, relax your mind, work with what is given, do not dream up other possibilities or "what if's".