A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.

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1answer
22 views

Accelerations of Cylinders

I got a box hanging from a rope that passes through an ideal pulley that attaches to the superior part of a Cilynder and makes it rotate. An exercise asks me two things: a) determine the magnitude of ...
3
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1answer
38 views

Differential equation of motion of combined rigid body

I am reading the following paper: http://tinyurl.com/jv2pu2m I have a question about (1) and (2): To (1), I think the following link provides good explanation. Equation of Motion for Rigid ...
3
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1answer
40 views

Force and Torque

Think of a uniform sphere. Sometimes if a force is applied to the sphere it does not only move but also spins. So there is a torque. But is it possible to calculate which part of the applied force is ...
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0answers
19 views

Moment Of Inertia, Angular Acceleration [on hold]

Consider a pulley and and a string is attached to the pulley with a mass hanging and then dropped. Explain why the acceleration is greater when you attach a string to a larger radius of a cylinder. ...
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1answer
194 views

How can angular velocity be constant even when there is a torque by friction?

A cylinder at rest lying on a rough ground is given an impulse which imparts a translational velocity (no angular velocity) to it. The question goes ahead with finding time after which rolling starts ...
3
votes
3answers
136 views

How to find the center of rotation? (2D)

First off, I'm assuming that a free floating polygon doesn't always rotate around its center of mass unless the net force is zero (based on the points below). If this isn't correct please tell me. ...
2
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1answer
56 views

Problem on rotation

So this is the problem:A wheel of radius of gyration k is placed on a belt moving with a speed v, which is maintained constant by means of an external agency. Assume that the axis of the wheel is ...
2
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0answers
53 views

What is the variation of pressure in rotating fluids(in accordance to the question in the image)? [on hold]

This is an interesting question that I came across. Please see attachment. It is a multiple answer type question. My answer was B and D. I have attached my derivation for this problem. I want to know ...
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0answers
50 views

Problem of pure rolling motion

A suspension, shown schematically as a spring of spring constant k, is connected to a sleeve able to slide without friction along a horizontal guide, and to a wheel (that is, a cylinder of radius R ...
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3answers
1k views

Has a body angular momentum and torque only in a circular path?

In different contexts, my book(Principles of Physics by Resnick, Halliday ,Walker) , they wrote For torque, the path need no longer be a circle and we must write the torque as a vector ...
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2answers
52 views

Lamina Pendulum Experiment help

I've been tasked with researching ways to find the gravitational acceleration g and its uncertainty together with the moment of inertia and and the moment of inertia's uncertainty. I have figured out ...
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3answers
38 views

How is rotational torque calculated when a force is applied uniformly over a surface?

Currently, the formula I am using to calculate the rotational torque applied onto an axis is $T = Fr\sin \theta$, where $T$ is the torque (in $\mathrm{N\ m}$), $F$ is the force acting, $r$ is the ...
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0answers
25 views

Verlet integration with translation and rotation in 2D

I'm facing with some equations of motion (translation and rotation) in 2D, and I need to integrate them using Verlet approach. Anyway, I'm stuck with the rotational part. In my framework, bodies lie ...
0
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1answer
30 views

Rotation and Momentum

I understand that according to one of Euler's theorems, any solid object's 3D rotational orientation can be represented by a single 3D vector and an amount, i.e. a 4D vector. However, is it correct ...
0
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2answers
319 views

A lever arm-definition question

My question is regarding Torque, and specifically the definition of the lever arm. As far as I've understood, the lever arm is the line perpendicular to the line of action to your reference point. ...
1
vote
2answers
122 views

Area moment motivation

I have some intuition about the (second) moment of inertia, and there is some motivation to define this concept if we think about the $KE$ of a rotating body or the torque $\tau$ applied, for example, ...
0
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1answer
39 views

Expressing angular velocity of solid body [closed]

The problem: We have a circular disk of radius $R$ and mass $M$ that is mounted on a rotation axis that is not the axis of symmetry of the disk. The moment of inertia with respect to the axis of ...
2
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0answers
130 views

Movement of a gyroscope with non-fixed axis

Assume one has a gyroscope rotating around an axis with both ends leaning on a dedicated semiplane as shown on the picture below. There is no friction either between the rotor and the axis or between ...
2
votes
2answers
130 views

Regarding (regular) kinetic energy and rotational kinetic energy

In my physics class we saw this problem: A disc of mass $M$ and radius $r$ is standing vertically and can rotate freely through an axis thats goes through its center of mass. A small particle of ...
6
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2answers
121 views

Equations of Motion of a Physical Pendulum [closed]

I would like to formulate the equations of motion of a particular type of physical pendulum, shown in the attached figure. The physical pendulum consists of a wheel rolling on a narrow board. A ...
0
votes
1answer
49 views

Would displacement vs time of circular motion be a sin/cos curve or parabola

If you were to graph the displacement from one specific point in a circle of an object rotating, example the boomerangs displacement from the thrower. Would you use a parabola, since in a cos/sin ...
1
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2answers
49 views

Finding relation between angular acceleration and liner acceleration directed in one direction

In the above given configuration what could be the relation between the angular acceleration of the rod $\alpha$ and the acceleration $a$ of the $2m$ block. My attempt : What I thought is that the ...
0
votes
1answer
25 views

How high does a slide need to be if the person at the bottom grabs a pole and rotates the pole 72 degrees?

My attempt: $mgh = \frac{1}{2}I \omega^2$ $\omega^2 = 2 \alpha\Delta \theta$, so $mgh = \frac{1}{2}I 2 \alpha \Delta \theta$ $mgh = I \alpha \Delta \theta = \tau \Delta\theta$ $\tau = rF\sin ...
0
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1answer
169 views

Why golf balls travel faster if they spin?

From the book I have been given to read I found that balls spin due to the centripetal force but i am confused about how exactly do the resultant force causes it to spin and move forward about the ...
5
votes
1answer
280 views

Sum of forces with liquid in rotation

It's not homework (I'm teacher). I would like to compute sum of forces on this study : The shape is symmetrical like that I'm sure the center of gravity is in the center of the shape. I compute ...
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3answers
214 views

Does center of mass affect how an object falls?

Suppose you drop an object which has two ends, of which one is heavy and the other is pretty light. Will the object fall with its heavier end downward or with the lighter one? Why does it happen?
0
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1answer
114 views

How to calculate torque needed to rotate a ring held captive between two parts with a known compression force?

I'm wondering how to find the torque needed to rotate a ring that is held captive between two plates with a known friction coefficient, radius, and compression force. I'm assuming that the mass of the ...
0
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1answer
30 views

Pure rolling between two moving sufaces

I know about pure rolling on one surface, where the ICR (instantaneous center of rotation) is the point of contact with the ground. But what if the the body is forced to roll between two surfaces ...
0
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2answers
28 views

Velocity of the points of a rigid body

The most general motion of a rigid body is a roto-traslation. Firstly is it correct that any point (let's call it $O$) of the rigid body can be seen as the point through which passes a istantaneous ...
2
votes
2answers
33 views

Torque and a pulley

I'm supposed to find, symbolically, what the moment of inertia of the pulley is using $T_1, T_2, r,$ and $a$. Obviously the base equation would be the sum of the torques equals $Iα$. I have the ...
0
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0answers
90 views

Uniformly/proportionally banking a rolling torus regardless of it's spinning speed [closed]

TL;DR I am working on a video game. Torus rolls down the hill. I want to make it turn. Instead of rotating it towards the expected direction, I am looking to bank it. Superbike idea, with just one ...
0
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0answers
23 views

Rotational energy of a celestial body

Let $M=2.8\cdot 10^{30}$ be the mass of a celestial body. We know that each year (earth year) his period increases by $11\mu s$. The power we receive of the radiational fog is $5\cdot 10^{31}W$. The ...
0
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1answer
39 views

Rotating mass and gravity effect [closed]

I'm a 57 yr old EE, but never had any mechanical physics classes. If we have a vertically oriented disc, affixed to an axle in bearings, 1m in diameter, with two 1kg weights attached at the outermost ...
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3answers
105 views

Does angular momentum of a system whose moment of inertia is changing remains constant?

An equilateral triangle $ABC$ formed from a uniform wire has two small identical beads initially located at $A$. The triangle is set rotating about the vertical axis $AO$. Then the beads are ...
0
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0answers
18 views

Moment of inertia of wheel-and-dart system

The problem I'm currently struggling with is: A wheel of mass M (assumed to be concentrated at its rim) and radius R is mounted horizontally so it may turn without friction on a vertical axle. (i.e. ...
2
votes
1answer
200 views

To prove uniqueness of the rotation tensor associated with rotation of a rigid body

Suppose there are $N$ particles embedded in a rigid body which undergoes some random rotation such that: $$ \overline{\overline {R}}_{ij} \otimes \vec{a}_{ij} = \vec{b}_{ij}$$ where, $i$ and ...
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5answers
367 views

Forces and acceleration on rotating objects?

Suppose you have an object undergoing uniform circular motion, with force vector pointing towards the center and another force vector tangential. Can it be said that the net force pointing in the ...
1
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1answer
45 views

Pendulum motion equation issue

The differential equation that gives the equation of motion of a pendulum where: $m$ is the mass $L$ is the distance between the pivot and the body's centre of mass $g$ is the acceleration due to ...
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0answers
7 views

Pointer to reference for rotational dynamics for large torques?

It's my understanding that when dealing with rotational dynamics (e.g., a gyroscope like at time=2155 seconds of https://youtu.be/N92FYHHT1qM?t=2155) that the equation for relating the speed of ...
0
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3answers
2k views

Different directions of frictional force when objects are rolling

My textbook has two instances of rolling bodies (smooth rolling). In the first, the body is rolling on the horizontal floor with some acceleration of its centre of mass. In this case, the book says ...
1
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1answer
15 views

Power needed to raise a bucket at a constant speed by a pulley

This is the last section of this pulley exercise: The bucket in is filled with water so its total mass is now $45$ kg. The bucket is raised at a constant speed of $2.0$ $ms^{-1}$ using an ...
3
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2answers
65 views

Pulley rotation

In the given arrangement, the friction in between the string and the pulley is enough to avoid slipping and the string is light. On the basis of these assumptions, would the tension in the upper ...
0
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1answer
25 views

How is a rocket mounted w.r.t. gimbal?

Gimbal system is used to balance the rocket from tripping after its launch. But, how is a rocket mounted with respect to the gimbal system?
0
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3answers
49 views

What does the “moment” in the moment of force or the moment of inertia refer to? [duplicate]

According to the Merriam Webster dictionary: Moment - a very short period of time Does the word "moment" in quantities like the moment of force or moment of inertia refer to this colloquial ...
3
votes
1answer
367 views

How do I treat the Lagrangian in the case of a rigid body?

Here's Exercise 1.11 from Goldstein's Classical Mechanics 3rd edition (the first one after having derived the Lagrangian basically): Exercise 1.11: Consider a uniform thin disk that rolls without ...
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0answers
29 views

Inconsistent Mass matrix in Euler Lagrange dynamics

I am trying to derive Euler Lagrange dynamics of a two body system that is translating and rotating in a plain. First body is given by $(x,z,\theta)$ where $(x,z)$ is position of the center of first ...
0
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3answers
938 views

Conservation of Angular Momentum, as related to a flywheel

Trying to work out some pesky flywheel dynamics for a project I'm working on, would love some for your assistance to better understand the underlying concepts. For a given flywheel (thin-walled ...
1
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1answer
34 views

Spinning top fixed point

I have seen many explanations about the movement of a spinning top. The explanations were in a varied level, from basic newtonian mechanics to Lagrangian formalism. But I do not understand why some ...
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3answers
70 views

Moment of inertia of 4 particle system

Four particles are connected by rigid rods of negligible mass. The origin is at the center of the rectangle. The system rotates in the $xy$ plane about the z axis with an angular speed of $6$ rad/s. ...
0
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1answer
210 views

How does ground interact with a box rotating around its corner?

I have some questions about how forces $F$, friction force $F_{friction}$, and normal $N$ interact in order to the box below to turn (clockwise) about the red corner, without sliding. The force $F$ is ...