This tag is for non-relativistic material strings, such as, e.g., a guitar string. PLEASE DO NOT USE THIS TAG for relativistic strings and string theory.

learn more… | top users | synonyms

21
votes
7answers
6k views

Why Won't a Tight Cable Ever Be Fully Straight?

I posted this picture of someone on a zipline on Facebook. One of my friends saw it and asked this question, so he could try to calculate the speed at which someone on the zipline would be going ...
6
votes
4answers
10k views

Rope tension question

If two ends of a rope are pulled with forces of equal magnitude and opposite direction, the tension at the center of the rope must be zero. True or false? The answer is false. I chose true though and ...
6
votes
5answers
619 views

Why do harmonics occur when you pluck a string?

When you energise a taut string, the following resonant modes of vibration occur: Plotting on the frequency domain, you can see their corresponding frequencies: But what is the underlying ...
5
votes
1answer
512 views

Lagrangian density for a Piano String

So I'm trying to do this problem where I'm given the Lagrangian density for a piano string which can vibrate both transversely and longitudinally. $\eta(x,t)$ is the transverse displacement and ...
4
votes
2answers
353 views

What happens when two strings collide?

I have a question, that perhaps someone with a much better understanding of physics can help me answer. Please correct me if I'm wrong. From what I understand, a string in string theory is basically ...
4
votes
2answers
271 views

Can the study of the quantum information structure in QFT with holographic duals be relevant to string theory?

I'm interested in characterizing the behaviour of measures of quantum information in strongly correlated quantum field theories which admit a gravity dual description, e.g through AdS/CFT duality. In ...
4
votes
1answer
227 views

About Holographic Model of Magnetism and Superconductor

I have a question about this paper http://arxiv.org/abs/1003.0010 In their model, when consider holographic paramagnetic-ferromagnetic phase transition, they need Yang-Mills field itself to ...
4
votes
3answers
969 views

Tension of rope. Different Answers?

The tension of a rope in a tug of war with unequal forces is equal to the least force on the rope. Am I right? (If group A pulls the wire with 20 newton leftwards and the group B pulls with 30 newton. ...
3
votes
1answer
5k views

Understanding tension

I'm trying to understand tension. So here it goes: I'll start from the beginning. Let's assume I'm in space and can move around and apply forces. Let's say a rope is attached to a body(which is in ...
3
votes
1answer
142 views

Boundary conditions on wave equation

I am having trouble understanding the boundary conditions. From the solutions, the first is that $D_1(0, t) = D_2(0, t)$ because the rope can't break at the junction. The second is that ...
3
votes
3answers
301 views

Why must the excitation of closed strings in String Theory be spin-2?

In String Theory it is predicted that as a result of the closed strings we have spin-2 gravitons. 1) How do we know there must be an excitation of spin-2 particles? 2) Why does a spin-2 particle ...
3
votes
1answer
259 views

Flux compactification

How flux compactification solves the moduli space problem in string theory? Please provide some details and, if posible, an example. Thanks in advance.
3
votes
1answer
108 views

Work done by vibrating string

figure from http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf The string has fixed ends, a mass per unit length of $\rho$, and is under tension $T$. This source claims that "the ...
3
votes
1answer
402 views

Why are there Gravitons among the modes of oscillation in String Theory?

Why are gravitons present among the modes of oscillation of the 'strings' in String Theory?
3
votes
1answer
78 views

Moments of vibrating string

I have to calculate first 10 moments for vibrating string with damping, but I don't know how to do it. I read about moments and in definition they mention linear system $$x'=Ax+Bu, \qquad y=Cx$$ with ...
3
votes
0answers
637 views

Shape of a string/chain/cable/rope/wire?

The height of a string in a gravitational field in 2-dimensions is bounded by $h(x_0)=h(x_l)=0$ (nails in the wall) and also $\int_0^l ds= l$. ($h(0)=h(l)=0$, if you take $h$ as a function of arc ...
3
votes
0answers
122 views

Polyakov action as broken symmetry effective action

I would like to ask if it is possible to regard the Polyakov action as an effective action that describes the broken symmetric phase of a more general model. Could someone draw an analogy with O(N) ...
2
votes
2answers
71 views

Pressure in waves on a string

We know that when we speak sound waves are created. The air particles compress and rarefy and pressure is more at the nodes and less at anti-nodes. But can we say the same thing about waves on a ...
2
votes
3answers
78 views

Why do these standing waves appear to be traveling?

Take a look at this video: https://www.youtube.com/watch?v=TKF6nFzpHBU You would expect guitar strings to produce standing waves, and in fact, the upper, thickest string does often produce long, ...
2
votes
1answer
433 views

How much is important the role of Planck length in the strings theory?

this is Planck length: $$\ell_p=\sqrt {\frac {G.\hbar}{c^3}} .$$ How much is important the role of this length in the strings theory? is this planck's length or newton's length! or maybe both of ...
2
votes
1answer
194 views

Wave on a guitar string, differential equation

The mechanical energy of an element of the string is : $$dE(x,t) = \frac{1}{2}\left[T_0\left(\frac{\partial y}{\partial x}\right)^2 + \mu\left(\frac{\partial y}{\partial t}\right)^2\right]dx$$ Where ...
2
votes
1answer
46 views

Beads flying out of flask

There is a popular youtube video of some metal beads being thrown out of a flask, literally hovering out of the container My question is how detailed a physical explanation of this phenomenon we ...
2
votes
1answer
175 views

Other Gross-Neveu like theories?

By "Gross-Neveu like" I mean non-supersymmetric QFTs whose partition function/beta-function (or any n-point function) is somehow exactly solvable in the large $N_c$ or $N_f$ or 't Hooft limit. ...
2
votes
1answer
376 views

Do Neveu-Schwarz conditions make sense?

When putting fermions on the string, we have to choose boundary conditions for our spinor fields - Ramond or Neveu-Schwarz. NS conditions on the closed string have antiperiodic conditions such as ...
2
votes
1answer
127 views

Finding the Shape of a Hanging Massive Wire

This came from a physics wave book. I have a static, massive wire on the x-axis, with a y-displacement due to a force per unit length $F_y$. I start with the equation $F_y = ...
2
votes
2answers
97 views

Where does a string tighten when you pull it?

I have the following setup: The string of negligible mass, causing little friction, is shown in dark blue and is fixed at the red circle. The taut string is shown in light blue (with excess string ...
2
votes
2answers
576 views

Guitar strings and temperature

I am investigating Mersenne's law with a guitar by varying tension (hanging weights) and string length. Will temperature change (room temperature to ~4°C) effect the frequency noticeably? If so, is ...
2
votes
1answer
249 views

How can Hilbert spaces be used to study the harmonics of vibrating strings?

The overtones of a vibrating string. These are eigenfunctions of an associated Sturm–Liouville problem. The eigenvalues 1,1/2,1/3,… form the (musical) harmonic series. How can Hilbert spaces be ...
2
votes
1answer
317 views

Drawbacks of Standard model

I am a graduate level student, interested in String theory. I was reading a paper on "String Theory and Einstein's Dream" published in Current Science, vol. 89, No. 12, p 2045, Dec. 25, 2005. and I ...
2
votes
1answer
25 views

Wave hitting a boundary with a mass on it?

If we have a transverse wave that is infinite in the $-x$ direction and terminate by a mass $m$, that is allowed to move in the $y$ direction at $x=0$ as shown in the diagram below: I think we can ...
2
votes
2answers
170 views

Nature of tension in a massless rope [duplicate]

I'm faced with a conceptual problem, where I am supposed to describe the motions of the following system (two masses on each end of a totally inelastic rope hanged on a pulley): I understand that ...
1
vote
3answers
1k views

Does the Fundamental Frequency in a Vibrating String NOT Necessarily Have the Strongest Amplitude?

I am doing some experiments on musical strings (guitar, piano, etc.). After performing a Fourier Transform on the sound recorded from those string vibrations, I find that the fundamental frequency is ...
1
vote
2answers
29 views

Waves on a guitar string

Can there be traveling waves on a string that is attached at both ends (like a guitar string), or does such a configuration allow only standing waves ?
1
vote
1answer
149 views

Tension in an Atwoods machine conceptual?

Assuming $T_1$ is the force that acts on box $1$ and $T_2$ is the force that acts on box $2$. Exactly what causes the Tension? Why does $T_1 = T_2$? The problem is we are told to memorize that ...
1
vote
3answers
807 views

Is it possible to whirl a point mass (attacted to a string) around in a horizontal circular motion *above* my hand?

I'm studying circular motion and centripetal force in college currently and there is a very simple question but confuses me (our teacher doesn't know how to explain either :/), so I hope we can sort ...
1
vote
2answers
337 views

How can particles being closed strings in String Theory create solidity in objects?

I understand how particles with certain masses can form to make atoms, which create solidity in objects due to Pauli's Exclusion Principle and what have you. These particles actually have mass and to ...
1
vote
1answer
70 views

Ratio of energy of normal modes of string

Suppose there's a wave on a string represented by fourier series: $$y(x,t) = \sum_{n=0}^{\infty} (-1)^n \frac{1}{2n+1} \sin(nx)\cos(nct)$$ I know the energy is $\propto y^2 n^2$, where $y$ is the ...
1
vote
2answers
98 views

Can we define tension in a string as the reactive force produced in a string being pulled at both ends?

In my textbook, the definition of tension was given that Tension is the reactive force which exists when string is being stretched at its both end. After it there was a case given that to calculate ...
1
vote
1answer
50 views

When do we assume that a rope has different tensions in different places?

Working a problem with 2 pulleys and masses in class this week the professor at one point assumed that the tension on the two sides of a pulley would be different. Every other time we've done a ...
1
vote
2answers
110 views

Which Force would help find the mass?

Two masses, A and B, are connected to a rope. A constant upward force 86.0N is applied to box A. Starting from rest, box B descends 12.1m in 4.70s . The tension in the rope connecting the two boxes is ...
1
vote
1answer
445 views

How do I recover the 1D wave equation from the Lagrangian?

Consider small displacements, $y(x,t)$, of an element of a string (circled in red and shown below) from equilibrium. The force balance in the vertical direction yields: $$+\uparrow \Sigma F: ...
1
vote
2answers
57 views

Derive Equation for Position of Antinode

I'm not sure what to do for this. The equation for standing waves on a string is given by: $$ y=2A\sin{(kx)}\cos{(\omega t)} $$ Use this equation to derive an equation for the position of the ...
1
vote
1answer
30 views

Can two bodies of different mass attached at ends of string passed over a frictionless pulley produce equal tension on both sides?

In my textbook there is given a case that to calculate acceleration and tension produced in string when string is attached at it's ends with two bodies of masses such that $m1>m2$ and the tension ...
1
vote
0answers
25 views

Non-linearity of a guitar pickup

I basically understand induction and why a pickup generates a signal. (From: http://www.brighthubengineering.com/consumer-appliances-electronics/64277-the-physics-behind-the-electric-guitar/) What ...
1
vote
0answers
26 views

Unusual waves and one of its parameter

I'm messing up with this java app on the web about waves on a string and i'm really curious about something. The java app is the following : ...
1
vote
0answers
27 views

Energy in a string [closed]

A nylon string of length L = 50 cm and under a tension of T = 70 N is plucked with an amplitude of 5 mm. What is the energy in the string? Please give me the relationship between energy of the ...
1
vote
0answers
1k views

Neglecting friction on a pulley?

So, this is how the problem looks: http://www.aplusphysics.com/courses/honors/dynamics/images/Atwood%20Problem.png Plus, the pulley is suspended on a cord at its center and hanging from the ceiling. ...
1
vote
1answer
253 views

A block, a string and Newton's third law

So this is a general force diagram of the system shown. My question is, according to the third law, if the block is exerting a force of magnitude mg on the thread in the down direction, then the ...
0
votes
4answers
68 views

Does increasing the tension on a string also increase the density?

Consider a string under tension, for example, a string on a guitar. When a guitar string is plucked, it vibrates at a certain frequency. When the tension on the string is increased by twisting the ...
0
votes
1answer
124 views

Solve hanging rope question by using Lagrangian density [closed]

for this one, I can only do the first(a) $$V_{total}=\frac{mg}{l} \int_{x_0}^{d-x_0}{y(x)\sqrt{1+(\frac{dy(x)}{dx})^2}}dx$$ and have no idea about others.