Submitted 1 year ago by Oneeightnine@feddit.uk to nostupidquestions@lemmy.world
Okay.
So we’ve got an entirely flat surface that also happens to be the exact same length as the earth’s surface.
If you had one continuous piece of string that went from one end of that flat surface to the other, and on one end there was attached a bell… would you be able to ring the bell by pulling on the other end of string?
Is the string a massless, frictionless, magic physics string that doesn’t stretch? Yes, you can ring the bell.
Normal real-world string? Probably not.
It depends what the string is made of. When you tug on one end of the string, you create waves that travel the length of the string at the speed of sound. The speed of sound depends on the medium, so if the speed of sound in the material that the string is made of is 50mph for example, then the wave generated by pulling the string will propagate at that speed until it reaches the other end.
The other consideration is the weight of the string. If you go to tug on one end of the string, but the rest of the string weighs thousands of pounds, then you probably won’t be able to tug it.
I couldn’t, no. But I’m very lazy and, as you said, it’s all the way over there
A string that long that doesn’t sag to the ground or break is already physically unlikely, but assuming it exists it would probably stretch enough to compensate for the movement. So I’d say no, unless you had a perfectly rigid string.
Yeah I should have emphasized that the string is perfectly taught, has no slack, isn’t affected by things like the wind and can’t break.
How dense is it? A string that long would have a lot of mass, which you’d have to overcome to ring accelerate the string to a speed that would ring a bell.
What about gravity and friction though? Because as it stands now, if the string was in a frictionless environment and was unaffected by gravity, then yes, you’d be able to ring the bell. However, the friction between the string and the earth over that kind of distance would require more pull strength than the string itself would be able to handle without breaking, unless it was made of some crazy strong material like some kind of nanocarbon alloy or something like that.
This truly is the string theory the people deserve
Sorry that we don’t all have string factories at our beck and call…
No one has really answered you so here you go. Yes you would be able to. It’s not instant though because information and energy cannot break the speed limit of the universe (speed of light). So essentially you’d pull the string and a few seconds later the bell would ring. Extend the string to the sun and it would take 8ish minutes for the bell to ring.
Speed of light is a lower limit but it would actually be the speed of sound in the material of the string that matters, so likely much slower than C
The speed of light is so much faster than the speed of sound, and that’s why sometimes you think someone is bright at first until you hear them talk.
:-)
Since we’re doing strings around the Earth, here’s the simplest, most unintuitive fact in geometry:
Say you have a string wrapped taut around the planet (purely spherical), like a belt. You want to raise that string up so that it’s one meter above ground all the way around the planet. How much more string do you need?
I’ll give you a hint. You don’t need to know the radius of the Earth to know the answer.
c = pi x d
So, to increase d by 2 meters (cause d = 2 x r), that’s 2 X pi, or 6.28 meters for string?
So I’m bad at math. Can you explain why we’ve decided to multiply pi by 2? Is there an articulable reason or is it just a rule?
c+x= pi * (d+2) in this case, right? So where did that multiply pi by 2 come from?
Good question. Many good answers. Put them aside and you still got a string made of multiple fibers that rub against each other. I’d guess that after a few hundred yards (depending on the string), the energy of your pull would be turned into heat by internal friction alone.
BrotherL0v3@lemmy.world 1 year ago
I did some numbers because it sounded fun.
Earth’s diameter is 41.804 million feet. I’m not sure if you meant that or Earth’s circumference when you said “Earth’s surface”, but I figure either one is gonna get us a really big number.
The first result I can find for string comes in a pack that weighs 2.89oz and contains 328 feet of string.
Using that as our standard, you would need 127,452 packs of string (assuming you find a way to perfectly attach them without wasting any length on knots).
127,452 * (2.89 / 16) = 23,021 lbs of string total.
So if we ignore the string stretching, compressing, or breaking, you’d only need to be able to pull 11ish tons of string to ring the bell!
NeoNachtwaechter@lemmy.world 1 year ago
It is true in principle. But the speed of sound is different, depending on the material. For that string we can assume it to be roughly 10 times faster than in the air.
~ 1 hour then.
piecar@lemm.ee 1 year ago
Wouldn’t the motion of the string move at the speed of the pull!? Assuming no compression.
NeoNachtwaechter@lemmy.world 1 year ago
But the weight of the string isn’t the force you need to pull.
sanguinepar@lemmy.world 1 year ago
Why not? If I try to pull a toy car alomg using a big thick rope, the weight of the rope is relevant, not just the weight of the toy car.
Zippy@lemmy.world 1 year ago
It kind of is. That is still 11 tons of mass. To ring a bell, you need to create some velocity on the striker. Pull a 11 ton mass in a frictionless environment will result in an extremely slow rate of acceleration. But in the spirit of the post, I suspect they are not considering how hard they are ringing the bell.
You are technically right though. Even blowing on a string long enough and you could accelerate it up to speeds approaching that of light. Providing there is no friction.
perviouslyiner@lemm.ee 1 year ago
Why would you use packs of string? Just leave the manufacturing machine running and don’t cut it into packs.