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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-2 votes
1 answer
116 views

Exceeding speed of light in simple mechanical setup

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 ...
-1 votes
1 answer
100 views

A paradox to law of conservation of angular momentum

I came across the following problem: A small body of mass $M$ tied to a non stretchable string moves over a smooth horizontal plane. The other end is being drawn into a hole with constant speed. Find ...
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0 votes
1 answer
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How does the net vertical force equation for a non-relativistic string derived?

In the following image from "A first course in string theory", we get the net vertical force of a string, dFv. While I understand the first equation, I don't understand how the second ...
1 vote
1 answer
115 views

How does the work done by a cord-over-a-pulley work? [closed]

I can use the integral of power with respect to time to solve problem. In this situation, what is the work done on the cart by the tension? Please do not use calculus.
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1 vote
1 answer
68 views

What is the constraint acceleration equation of the system? [closed]

In the question there is a hint given, $y_A$ is not constant. From this hint I began to look at the pulley that holds $m_1$ and $m_2$, and can see that it has the same tension as $m_3$. From this ...
2 votes
6 answers
422 views

What is the centripetal force when a bar rotates about its center of mass?

Scenario 1: The centripetal force acting on the ball towards the center of rotation is $\frac{mv^2}{r}$, where $m =$ mass of the ball, $v =$ magnitude of the instantaneous linear velocity of the ball,...
1 vote
1 answer
78 views

Sound of string in a guitar

I study about waves and I learn that the velocity of a transverse wave in a string depends only on the tension and the density of the string. The frequency depends only on the source (whatever ...
-2 votes
1 answer
80 views

Why is the acceleration of $m_2$ downward?

The magnitude of the acceleration of $m_2$ is $a$. It does not say in the question whether it is downward or upward. But the answer assumes it is downward. So I think either it is badly framed, or it ...
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7 votes
3 answers
749 views

What physical state of a wound string corresponds to a 'tuned' string?

Many instruments can be strung with strings comprised of a solid core and wound with another metal wire, e.g. the viola. I was wondering about the physical state of wound strings when they are 'in ...
0 votes
4 answers
175 views

What is Tension in a string? How is it produced at a molecular level?

I can't understand the direction of tension. Why is the direction of tension at the ends of a string away from the object or block of mass? Can someone tell me what happens internally in a string? ps: ...
1 vote
1 answer
31 views

What is the difference between these two falling rope motion?

Here are two falling rope problems in Marion's Classical Dynamics Textbook and both equations of motion given by manual solution. (There is a typo in the third line of solution 9.15, one of the terms ...
0 votes
1 answer
49 views

Work of the tension acting as the centripetal force in a circular motion of varying radius

Consider this arrangement: A point mass (its mass being $m$) is executing uniform circular motion on a frictionless horizontal plane. A string passing through the center of the circle and attached to ...
-1 votes
3 answers
95 views

When to use positive and negative $\rm g$ when calculating force?

My teacher gave us a question the other day: A $20\ \rm kg$ sign is supposed to hang from a pair of wires attached to the wall and support beam as shown in the diagram. The worded that will be used ...
0 votes
1 answer
32 views

Motion of non-homogeneous string fixed at both ends when pulled at a point

How to solve displacement and velocity profile of string which has density $d_{1}$ till distance $x$ and density $d_{2}$ from $l - x$ to $x$ fixed at both ends and when given initial displacement and ...
2 votes
1 answer
84 views

Determining the equations of motion for a 2 DOF in 2 directions

I'm having trouble understanding a 2DOF system that moves in 2 directions. The problem asks me to determine the EOM for a system shown in the attached image: My first idea is to transform this system ...
1 vote
1 answer
31 views

Constraint rate change problem [closed]

Two small rings O and O' are put on two vertical stationary rods AB and A'B' , respectively. One end of the inextensible threads tied at point A'. The thread passes through ring O' and it's other end ...
2 votes
2 answers
58 views

What happens when I grab a rope after jumping down?

If a body has a mass of 54 kg and falls straight down for 11.33m before grabbing a rope, what are the forces acting here? What part does the coefficient of friction between the rope and hand play?
0 votes
2 answers
40 views

When the tensile force is equal to the weight of the body

I have met a lot of problems where the tensile force is different from $mg$, while in this one problem in the solutions it is written only that the tensile force is equal to mg. So if someone has time ...
0 votes
0 answers
41 views

Why while solving some specific problems like this we need the second-order variation like this one?

Consider a string which is fixed at both ends and we are giving it a small amplitude by tauting it and moving to and from. If someone wants to derive the wave equation of the string, they would first ...
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1 vote
4 answers
174 views

What is positive rotation direction of a pulley in the Atwood machine?

In the Atwood machine the mass $m_1$ hangs on the left and $m_2$ hangs on the right, with $m_2 > m_1$. When released from rest the system accelerates clockwise which we define to be the positive ...
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2 votes
2 answers
113 views

What exactly happens, step by step, in string harmonics?

I know that a string when plucked shows harmonics but I do not really understand how. Like, I understand resonating air column and how standing waves are formed there, but I can't seem to get the step ...
6 votes
2 answers
412 views

Why does plucking a string produce harmonics instead of a pulse?

If I jerk a wire from the free end fixed at an end and then fix the free end, it will produce a pulse travelling back and forth between the two ends. So in a string fixed at both ends, if we pluck it ...
0 votes
1 answer
41 views

Why do we feel weightless while free fall but not while hanging with a string?

So why do we feel weighted by hanging on a string as their is no normal force acting on the object only tension force on the string not on object
0 votes
2 answers
53 views

Angular Momentum Conservation..04

A stone is attached to a string and is revolved in a circular path with constant angular velocity $\Omega$. In this state its angular momentum is $L$. If the length of the string is reduced to half ...
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0 votes
1 answer
42 views

What the reason for not taking contribution of gravity when a wave is propagating?

Suppose a wave is being transmitted from one end of rope to other , for small amplitudes the wave speed is √T/u , suppose now that amplitudes of wave are not small and that gravity is also need to be ...
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0 votes
1 answer
30 views

Question about the modulus of elasticity of a half-string

Question The ends of a light elastic string of natural length 0.8m and modulus of elasticity $\lambda$ N are attached to fixed points A and B which are 1.2m apart at the same horizontal level. A ...
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2 votes
0 answers
86 views

Taut strings in curved spacetime

In general relativity, a straight line is defined (or, in a sense, replaced?) by the path a light beam takes. In Newtonian physics, another way to approximate a straight line between two points is to ...
0 votes
2 answers
42 views

Determining moment and accelerations of blocks connected through rope and pulley [closed]

A pulley, of radius $r$, mass $m$ and moment of inertia $I$ with respect to the axis orthogonal to the vertical plane where the pulley is positioned and going through its center, two masses are ...
1 vote
1 answer
75 views

Standing wave in a string clamped at one end

*In the case of a standing wave formed with one end clamped (fixed), there is an anti-node at the free end irrespective of the overtone. My question is why is there has to be an antinode. Is there any ...
0 votes
0 answers
32 views

How do (if) the relative paces of time differ in these circular motions?

I) Imagine two equal masses tied tethered together by a rope in empty space. The rotate around their COM in the middle of the rope. The masses don't cause gravity. The masses don't move wrt one ...
0 votes
0 answers
33 views

Why $T$-transformation is a symmetry in $d=4$ pure Maxwell theory?

The Maxwell $\theta$-term $\mathcal{S}_{\theta}=\int d^4x\frac{i\theta}{32\pi^2}\epsilon_{\mu\nu\rho\lambda}F^{\mu\nu}F^{\rho\lambda}$ has the identification for theories have $\theta$ and $\theta + 2\...
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1 vote
1 answer
52 views

Analysing a system of pulleys? [closed]

I'm quite unsure on how to solve these questions. For part (b), my approach was that the tension in the lower cable would have to be greater than or equal to $2m$ for both the masses to be lifted. ...
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0 votes
1 answer
63 views

2D statics problem with 5 unknowns? [closed]

In this problem there are 2 hinges (each one with 2 reaction) one at point C [$C_x$,$C_y$] and the other at point G [$G_x$,$G_y$] , Also there is a cable that Dc that has tension $T_{DC}$. Then how ...
1 vote
0 answers
63 views

Tension in a stretched string

I am working my way through Alistair Rae and Jim Napolitano's Quantum Mechanics textbook (sixth edition). In the introductory section, the example of a stretched string is used to derive the wave ...
-1 votes
1 answer
106 views

If you hang a mass with a rope on a wheel, how do you calculate the resulting moment of inertia?

How do you calculate the moment of inertia of the left object with axis of rotation in M. Is it the moment of inertia of the wheel $I$ and the $m *r^2$, where $r$ is the position vector of $m$ w.r.t. ...
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0 votes
2 answers
78 views

Why do these 2 different methods of finding tension in a string give 2 different answers?

A uniform rod BC of length $L$ and weight $W_1$ is hinged to a fixed point at $B$. A particle of weight $W_2$ is attached to the rod at $C$. The system is in equilibrium by a light elastic string in ...
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1 vote
1 answer
75 views

String stretching mathematics in string theory

In, Lecture 1 | String Theory and M-Theory by L. Susskind he says that some strings can be stretched to without the string snapping because they have a constant tension. If im not mistaken he was ...
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0 votes
2 answers
72 views

A complex pulley system with one string [closed]

I was doing some pulley block problems, and one of the concepts used is tension in a massless string is same everywhere. Also the tension on the string with which the pulley is connected is twice the ...
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-1 votes
1 answer
67 views

To prove this equation for pulleys: F = $\frac{NPF}{Total mass}$

Given: inextensible string , massless string. There is a concept to find acceleration in pulley system quickly. It is that: $a=\frac{\text { Net pulling force }}{\text { Total mass to be pulled }}=\...
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0 votes
0 answers
36 views

Slackening of string in vertical circular motion

My physics teacher says that in vertical circular motion of a mass $m$ connected to a string, the tension in the string will become $0$ (i.e. the string slacks) when the radial component of the force ...
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0 votes
1 answer
110 views

How does a rope's tension work?

A problem I encountered is as follows: A pulley consists of a circle of radius $R$ is pivoted about a point a distance $R/2$ from the circle’s center. A string attaches to a block hanging from the ...
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0 votes
2 answers
44 views

Force acting on two wires due to a rod

Here a rod of mass $M$ is hung with the help of two cylindrical wires marked with yellow and red colors. We know the weight of the rod is acting on the center of gravity of the rod(mid point of the ...
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0 votes
2 answers
46 views

Please help with this equation of tension in a transverse string

I always assumed tension is uniform in a wave but i saw a question in which we had to form an equation for tension at different position and time. The answer given was $$ T \sqrt{ 1+\left(\frac{\...
0 votes
1 answer
79 views

How to figure out the free body diagram?

This was the part of the Motivation to the definition of Green's Function. I am referring this problem from the book Ordinary Differential Equations by Tyn Myint-U. I am not able to figure out the ...
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3 votes
1 answer
157 views

What exactly is the natural frequency of an object?

My book defines natural vibrations as: THE PERIODIC VIBRATIONS OF A BODY IN THE ABSENCE OF ANY EXTERNAL FORCE ON IT, ARE CALLED NATURAL VIBRATIONS.THE TIME PERIOD IS CALLED ITS NATURAL PERIOD AND THE ...
3 votes
2 answers
241 views

Justification for constant tension in transverse wave on a string

It is common in the derivation of the transverse wave equation on an ideal string to assume the tension along the rope is uniform in the limit that $$|\partial \psi / \partial x|\ll 1.$$ However, what ...
0 votes
1 answer
75 views

Static equilibrium | A beam is hanging by two ropes with angles and there is a block on it [closed]

I have this problem model and I'm trying to get the solved equations for the distance $d$ and the tension $\vec{T_2}$ with the known values of angles $\alpha$ and $\theta$, $\vec{P_1}$, $\vec{P_2}$ ...
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1 vote
1 answer
46 views

Freely Moving Cloth Clip on a String

A cloth clip is kept on a rope such that it can move freely along the rope. The rope is slack, (but tied at two end such that the clip cannot escape), is rotated at a high speed for a substantial time ...
1 vote
2 answers
90 views

Why do guitar strings behave so nicely?

To explain the harmonics on a guitar string, we use 2D models of the string. For example we assume that the string can only go up and down. But the string is inherently a 3D object and it could ...
0 votes
1 answer
63 views

What kind of motion will a string behave when the condition to form stationary waves is not met?

We know that stationary waves can only form when the wavelength of the wave and the length of the string satisfies certain conditions. My question is, how will the string behave when this condition is ...

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