# Questions tagged [string]

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.

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### Does rope in a standing wave expand and contract as it moves between being straight vs sine?

Images of standing waves often show two people using a jump rope. The shape of the rope goes from straight to waves to straight, then a sine wave the other way and then straight again as it repeats. ...
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### Forces Problem from Halliday, Resnick and Krane [closed]

To my knowledge, the net force on $m_1$ is $T - m_1 \cdot g \cdot \sin(\theta_1) = m_1 \cdot a$ assuming that the block accelerates up the incline. However, the solutions manual states that the ...
29 views

### Forces in a rope (tension) [duplicate]

I am confused with the concept of tension in a rope. Look a the diagram. Two forces are acting in a body, in this case the body is a rope, hence the total force in the rope should be zero, right? So, ...
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1 vote
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### Circular motion after tension gets zero

If we have an object rotating in a vertical plane, with a cord which cannot extend (has fixed length), what happens after the tension goes to zero? How do I prove mathematically that the trajectory ...
79 views

### Would the string break? [closed]

Thinking about the Bell's string paradox, I came to this thought: Would the string break - I mean a real string with some resistance -, if in the Bell's paradox we change the "constant proper ...
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### Why does particle leave circular motion after string slacks?

If a particle is attached to a string and made to move in a vertical circle with initial velocity of $\sqrt{4gl}$ $m/s$ where l is the length of string, at some angle (approx $131°$ with the initial ...
60 views

### Can someone provide the solutions to these questions asked in my exam in my high school [closed]

In the arrangement shown in the figure, initially the block of mass 'm1' is in limiting equilibrium. The coefficient of friction between the block of mass m1, and floor is 'u' Now the particle of mass ...
27 views

### Problem related to adiabatic invariants [closed]

A simple pendulum is oscillating in the gravity field, while its length slowly decreases with time. Determine amplitude of the small oscillations $A$ of the bob, when length of the oscillating part of ...
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### Tension in Atwood machines [closed]

Assume massless pulleys and strings. Going from up to down, pulleys are labelled 1,2,3,4. I am trying to grasp how tension is passed from string to string. My intuition tells me that starting ...
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1 vote
44 views

### Why is the self-weight of a cable not uniformly distributed?

I have learned that a free cable that is hanging with only its self-weight to consider will form a caternary while a cable with a uniformly distributed load forms a parabola. Why is the self-weight of ...
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### Tension Problem (Classical Mechanics) [closed]

An exercise from my textbook revealed to me that I have some misconceptions about Newtonian mechanics. The textbook gives the answers to the questions, but I'm hoping someone can explain how it works ...
130 views

### Finding force in a constraint motion problem [closed]

I have a doubt regarding the correct method to solve this question. A bead of mass $m = 0.5kg$ which can slide along a smooth horizontal rod is attached to one end of a light inextensible string of ...
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1 vote
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### Virtual work method in pulley [closed]

The problem illustrates two pulleys whose two ends are going downward with velocity $v$. The problem was about finding the velocity of the point $X$ i.e the point where the strings of the two pulleys ...
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### Deriving wave equation of string without approximation

When deriving the equation for a standing wave of a string, we often approximate that the tension at all points in the wave is constant. but I want to derive the equation without the approximation. I ...
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### For two strings tied together: Why does a sinusoidal incident wave give rise to sinusoidal reflected and transmitted waves? [duplicate]

I am reading Griffiths' Intro to Electrodynamics (Section 9.1.3 Boundary Conditions: Reflection and Transmission) where he analyzes the case of an incident wave sent down a string that is tied to ...
1 vote
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### Catenary curved string with differing linear densities - Linear density distribution

Do you guys know if there's some kind of weight distribution that fits a problem like this one? Let there be a string with two different sections with different linear densities, like the following ...
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### Details on the string theory being a quantum gravity theory [duplicate]

So since string theory is a quantum gravity theory, how can we derive from string theory to Einstein gravity equation when $\hbar \rightarrow 0$, as what we did from quantum theory to classical theory?...
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### Can the wavelength of the standing wave be different from the wavelength of the sound it emits?

I have a question about standing waves on strings. I'll try to explain the best I can, I searched and researched the whole day yesterday but I am confused still: Every frequency has a single, and ...
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### How does a string "distribute" tension?

This question deals with a massless, inextensible string. The problem arises with the question below. We know by Newton's third law that the force a body will apply on the string will be equal to the ...
1 vote
75 views

### Why is the potential energy of a suspended rope proportional to the stretch?

In A. Zee Einstein Gravity in a Nutshell, when he is talking about variational calculus on page 113, he gives an example of a suspended rope. To calculate the total potential energy due to tension, it'...
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### Some confusing points about Bell's spaceship paradox from a video

I was looking this video about Bell's Spaceship Paradox on Youtube titled This Paradox Took 17 Years To Solve. It's Still Debated. Please note that the video starts at the segment I have a question ...
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1 vote
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### Energy conservation in a system of two bodies

I have no idea why my previous post was marked as a homework question where the solution was clearly visible. I was asking to clear a concept of mine regarding system of bodies. However,i will keep ...
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### What is not inverted when a string wave reflects with phase reversal?

When a wave reaches a boundary and it is reflected, it may happen that, if certain conditions are fulfilled, there is a phase reversal (180$^\circ$), so that what came as a crest becomes a trough and ...
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### How can I calculate the number of nodes on a plucked string?

Given the length of the guitar string, can you predict the number of nodes that would exist on that string? My textbook says that there are an infinite number of harmonics that can be created when a ...
87 views

### Can anything be a system?

I was doing some problems on Newton's Laws of Motion, and I found out that the solution arbitrarily considered anything as a system. For example, in this question on pulleys, the solution simply took ...
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### Why is the tension force in a rope with two different forces acting on it uniform? [duplicate]

Let me explain myself. Imagine a massless rope over a pulley, two weights m1 and m2 attached to the ends of the rope. M1's weightforce (m1xg) exerts a force on the rope, call it T1. On the other end ...
1 vote
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### Is it possible to find Tensional force from Lagrangian?

The Lagrangian principle is easier to solve than any kind of problem. But, we always "forget" (not really, but we don't take it into account directly), of Tension in a system when looking at ...
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### How does the tension exactly act on the pulley?

Everyone says that $T_1$ and $T_2$ will act on the patch of pulley wrapped by the string. So do they act on arcs $AB$ and $CD$ respectively? If not, then how do they act? And if $T_1 = T_2 = T$, they ...
1 vote
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### String vibration under periodic boundry conditions

I wish to known which are the vibration modes (in case that they exist) of an string vibrating under periodical boundary conditions (PBC). The question is related to molecular dynamics simulations of ...
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### Is it really the Tension in the rope that pulls the pulley?

We always solve questions by drawing two tension forces at the diametrically opposite end, to show that tension is pulling the pulley, but from the research I have done, it is clear that it is not ...
52 views

### Falling stones attached by a string

Suppose we have two stones, one "big" (A) and one "small" (B), the smaller one over the big one at the moment of free fall. Suppose also that a string of a certain length is ...
1k views

### Transverse waves in a rope: Why does tension not increase?

So I've gone down the "waves" rabbit hole... I found out that the propagation speed of transverse waves in ropes depends on the tension in the rope. At a first glance, this intuitively ...
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### How does massless particles arise in string theory when it starts with the assumption that all strings are composed of massive little pieces? [duplicate]

I saw in a lecture (see after 00:55:00) by Leonard Susskind, he write Polyakov action, saying that the string is supposed to have divided into several pieces with mass (he says that it is the non-...
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### Hooke's law and modulus of elasticity [closed]

I'm having trouble in understanding the following question which state modulus of elasticity in Newton. Is it possible that we can define modulus of elasticity in Newton somehow?? I am getting a wrong ...
1 vote
63 views

### How do I find the constraint relation in this question?

Let $\alpha_1$ and $\alpha_2$ be the angular acceleration of top pulley and bottom pulley respectively while $a$ is the acceleration of centre of mass of bottom pulley. Then, $$\alpha_2r+a=\alpha_1r$$ ...
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1 vote
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### Cosmological expansion around ropes between galaxies

The FLRW cosmology is a fair approximation of cosmological expansion for space between galaxies and clusters, however within galaxies themselves, is known to not hold, and in fact observational ...
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### Elemental problem of dynamics

Ok, let's go fast. If we have the following system, and we want it to be static (acceleration = 0), we will always and obligatorily need friction, or any other force to oppose those existing in the ...
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### How do i calculate the tension in string here? [closed]

How do I calculate the tension of string? I have already calculated the acceleration of the 2 masses which is 3m/s. But I can't seem to arrive at the answer which is 9.00N. Sorry if this was a ...
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### Determine which ropes are under tension in pulley systems

These questions is gotten from beer and Johnston vector mechanics, the solution manual reveals: i) the two portions ropes are under tension in (a) - this I understand ii) only two out of the three ...
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### Tension in thread

We know a thread or string experiences the same tension force throughout the whole length,but when we tie a knot in the thread,why does the tension force become different in the two sides of the knot? ...
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### Can tension change in a massless string if there are three forces acting on it?

Consider this massless string, which has three forces acting on it, two on the ends and one at the middle: Would the tension change at the midpoint where the $5 \text{N}$ force is applied? I think it ...
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### What does it really mean to have infinite tension?

Let an object of mass $m$ lie on a wire. The wire is much smaller in mass than the object and so its mass can be negligible. As the object lies on the wire, the wire is pulled down to a position where ...
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### Analogies for the Behavior of the Wave Function

In an overview of Quantum Field Theory, I recently heard the behavior of an elementary particle compared to that of a plucked (bowed) string. Although the stable states of excitation of the string are ...
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### What subfields, or specific works/articles, would cover the "the physics of ropes"?

Undergraduate student here. Yes, this is very similar to a post I made a year ago, however, as this topic is now pertinent to the research I plan to undertake, and now that I have distilled the idea a ...
1 vote
75 views

### Why does a pulley rotates?

I have beening dealing with problems involving pulleys. It seems like a pulley is something that changes the direction of a string, and it rotates when the string moves on it. Why do we need something ...
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1 vote
75 views

### Confusion about tension and disk

Why are the two tensions not equal? I thought tensions on two ends of a cord are always equal. And are the motion of the disk caused by friction force due to the motion of the cord and disk surfaces?
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### How to find accelerations/tensions here? [duplicate]

$m_{2} = 6 m$, $m_{1} = m$, $m_{3} = 3 m$ I used conservation of string length and got $a_{3} + a_{pulley} + a_{1} = a_{2}$ and $T_{1} = 2 T_{2}$, but I have a feeling it's wrong because if the pulley ...
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### Need help confirming answers; Laws of Motion Problem

I just recently started reviewing my old textbooks for fun (don't judge), and I'm having trouble wrapping my head around tension forces in this review question for the Laws of Motion chapter. Before ...
1 vote Suppose a system as shown. If i pull block $m1$ and $m2$ (the two side masses) with speed $v$ and theta is the angle mentioned the speed of central block becomes vsectheta in vertical direction. If ...