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

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Who told us how to measure torque?

We all know that force and torque are physical quantities which we have defined according to our purpose of work. Now we are all aware that Newton's Second Law from his Laws of Motion states how to ...
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1answer
165 views

Moment of inertia of disk with off center hole [closed]

So I am given the figure shown below and told to find the moment of inertia if we have that the mass of the shaded region is $M$. I think I have to find the total mass without the hole and the mass ...
2
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1answer
58 views

Why is friction not dissipative in rolling motion? [duplicate]

We know that non-conservative forces like friction is a dissipative force. But according to my book when a solid cylinder is rolling down a rough inclined plane of inclination angle $\theta$ the ...
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0answers
53 views

What does hinge reaction mean ? How do i calculate it? [closed]

I recently came across a lot of problems where components of Hinge Reaction were asked along different axis . My questions are : A) What does hinge reaction mean ? B) Does it change ...
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0answers
51 views

Stabilizing a rotating wheel with a changing center of mass

Imagine a rotating wheel. For simplicity's sake let's assume it's not under the influence of any significant external forces (including gravity). This wheel is hollow, and objects inside are ...
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2answers
65 views

How is direction of static friction not opposite in direction but perpendicular when dealing with centripetal forces?

I was trying to wrap my head around this solution, and the whole idea of a car moving around a level curve, how the friction supplies the centripetal force. But I still can't wrap my head around the ...
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1answer
61 views

How do I properly apply the parallel axis theorem to a rod-sphere system rotating about its center of mass?

In the image below you see a rod with a sphere attached to its right side. The rod-sphere system is rotating around the entire system's center of mass. How do I apply parallel axis theorem to find the ...
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1answer
8 views

Calculating the force $F$ for wich $S_2$ will be in uniform motion

The sketch is given: The double pulley groove of radius $r=5\;\mathrm{cm}$ and $R=10\;\mathrm{cm}$ is in rotation Two inextensible wires of negligible masses are wound around ...
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0answers
57 views

Tension in a rod rotating about a fixed point

A rod of mass $m$ and length $l$ is rising about a fixed point in the ceiling with an angular velocity $\omega$ as shown in the figure. Now, on taking a small element on the rod, the net tension ...
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2answers
76 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. ...
0
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1answer
82 views

Is angular acceleration same about all points of a rotating ball?

Suppose a ball is rotating due to force $F$ applied at its top (on a rough ground).There is pure rolling. In one case we write the equation w.r.t COM i.e $F.R=I(\alpha_1)$ and $F-f=ma$ and ...
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0answers
71 views

Spinning a rope when hanging, what is the curve? [duplicate]

Holding a rope from one end and spinning it. As shown in the picture, what will be the curve of it?
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2answers
70 views

Rotational speed of a planet [closed]

Is there a way to calculate the rotational speed (or day length) of a planet? If not then what are the factors? I mean what affects the speed? Is it just the distance from Sun (like period of a ...
1
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1answer
72 views

Mercury's rotation, Disturbation's caused by thermodynamics

Mercury rotates sychronized like two-stroke machine. As it's solar day is 2 mercurian years.(Orbital periods) Or should we say 3:2-stroke machine, as it's Orbital period is 87.969 Earthdays, and it's ...
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0answers
65 views

Precession of angular momentum vector

I'm studying Classical Mechanics on Goldstein's book, so I'm using his terminology and notation. First I'll explain where the question comes from: consider a heavy symmetrical top and consider the ...
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1answer
47 views

3D Dynamics: determining the moments of inertia on a plate with a couple

My Mechanical textbook (Bedford & Fowler 4th Edition) has a worked out example for determining a couple using euler's equations. This is not a homework question (at least I don't think it is?), ...
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3answers
57 views

Is Conservation of Energy maintained when the orbit of a rotating mass increases in diameter?

I read an example where someone was explaining how the law of conservation of energy does not have to be maintained within a rotating mass even though angular momentum is maintained. The given ...
1
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1answer
55 views

When does an object rotates and translate at the same time?

I have a ruler on the table. If I push it with my finger on its end, it will rotate. but if I push it hard enough, it will rotate and slide slightly. Which force cause this sliding motion? and how ...
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1answer
71 views

How to conserve angular momentum?

If i want to conserve angular momentum from the point of contact of the solid sphere and the ground how should I do it? I know we can use $mvh = I\omega + MvR$ ,if the collision is elastic. But in ...
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0answers
66 views

Uranus, the Physical model to change it's rotation axle

Uranus rotates pretty wierd, it's 90-degrees tilted; Why is Uranus's axis of rotation tilted? The best answer for this is; that at a distant point in its past, Uranus was struck by a very ...
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1answer
45 views

Rotational Energy homework question

A hollow sphere rolls along floor and goes up 30 degree incline, how far up does it stop? Ok so from what i know you need conservation of energy: $mgh=$rotational energy And $h$ is $d\sin(30)$, ...
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3answers
125 views

How did planets start to spin and do all of them spin in same direction? [duplicate]

How did planets start to spin in the first place? Some say that gases which condense and form planets start spinning and hence planets acquire a spin. And some say that they start to spin to conserve ...
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3answers
205 views

Acceleration of body rolling down inclined plane

Acceleration of a body rolling down an inclined plane is given by: $$\frac{g\sin\theta}{1+\frac{k^2}{r^2}}$$ $g$=acceleration due to gravity $\theta$=angle of inclined plane $k$=radius of gyration ...
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1answer
79 views

A particle of mass m slides down the frictionless surface from height h and collides with the uniform vertical rod of length L and mass M [closed]

A particle of mass m slides down the frictionless surface from height h and collides with the uniform vertical rod of length L and mass M. After the collision, mass m sticks to the rod. The rod is ...
0
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1answer
42 views

Acceleration of two points problem (mathematical explanation)

There is a square board with two nails in corner A and B. We apply a torque $M$ to the square board. Nail A can move freely on a track only in the $x$ direction and B only in the $y$ direction. The ...
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4answers
426 views

Earth's Kinetic energy change

Earth's rotational speed varies. I have checked the data an found following Peaks; Year 1998, 23.May, the Earth rotated in 86400.0023738 seconds. At 9.July the rotation time of the Earth was ...
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0answers
19 views

integrating small angular velocities

I know that for a constant angular velocity the following is true: $R=e^{W t} R_0$ where $W$ is an angular velocity tensor, $t$ is a time, and $R$ is a rotation matrix I believe the following is ...
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0answers
26 views

Determining Attitude from Angular Velocity History

I am doing an analysis concerning the torque-free motion of an axisymmetric body. The angular velocity is given by $\omega(t) = [\omega_t\ sin(\Omega t), \omega_t\ cos(\Omega t), \omega_{z0}]$ From ...
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0answers
21 views

Proof formulas of tangential forces [closed]

Only a tangential force F is applied to a particle. A and B are two constants that are determined by the initial conditions. show:
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1answer
146 views

Intuitive Explanation of Tippe Top Effect?

A friend showed me a tippe top (a special kind of spinning top) lately and asked me about the physics behind it. I thought about it for a while but cannot quite figure it out. So I will throw the ...
2
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1answer
75 views

Why can we model a body to have a center of mass?

I accept that bodies have a center of mass. I also accept that if I were to suspend a body by only supporting it at its center of mass, then the body wouldn't rotate. In the scenario that we suspend a ...
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1answer
38 views

Circular Motion and Simulated Gravity

People have proposed that a spinning cylindrical shape could be used to simulate gravity. Will gravity be simulated if the cylinder is frictionless? My brain can't seem to wrap around the idea that ...
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1answer
156 views

Finding torque due to normal force [closed]

A cubical block of mass $m$ and edge length $a$ slides down a rough inclined plane of inclination $\alpha$ radian with a uniform speed. Find the torque of the normal force acting on the block about ...
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2answers
80 views

How do you choose direction of moment of inertia?

If a car is accelerating forward from rest with no air resistance while weight and normal forces act on the wheels, in which direction is the moment of inertia? Is it positive, clockwise or anti ...
0
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1answer
67 views

Doubt related to rotational motion (rolling down an inclined plane)

I have doubt regarding when an object ( sphere , ring , cylinder etc ) rolls down a FRICTIONLESS inclined plane. Let us suppose the angle of inclination of inclined plane is θ. Now the forces acting ...
0
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1answer
56 views

Relation between accelerations of block and tangential acceleration of the pulley in pulley block system

I was doing some pulley block problems in rotational mechanics and almost everywhere when the pulley is rotating and some masses are connected by a light rope(for example I am taking a two block and 1 ...
0
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1answer
33 views

How do I calculate the speeds in x, y, and theta of a spinning rod?

Suppose the object looks like the diagram below (it is the horizontal rod). On the vertices, are two velocity vectors $v_r$ and $v_l$. The question is: how is the motion of the rod affected by these ...
2
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0answers
106 views

Lagrange: when a potential force, when a generalized force?

Consider the following case of a drum unrolling a mass that is on a massless string wrapped around the drum: According to my professor, here we must consider the mass $m$ being in a gravitational ...
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1answer
85 views

Contradiction in a simple torque/rotation problem - two ways of calculating external force don't agree

Suppose we have a rigid system of two point objects (both of unit mass) connected with a massless rod, with the objects horizontal on the x axis, at a distance $r_1$ and $r_2$ from the origin, ...
2
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1answer
159 views

Lagrangian in rotating reference frame

I have a homework question I am working on, and I'm stuck on the last term in this proof. The problem states: Question: Consider a primed set of axes coincident in origin with an inertial set of axes ...
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1answer
74 views

What is the force that stops a rotating wheel eventually? [duplicate]

Assuming a car is traveling on a road. At some point, the driver stops accelerating the car, so it travels some distance and then stops. Since the car's wheels are round and are rotating without ...
2
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3answers
200 views

Sign of torque when rolling an object down an incline

Suppose you have an object rolling down the incline at 30 degrees. Given the point of contact is instantaneously at rest, I decided to analyse torques at that point. Therefore, the only force ...
0
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2answers
93 views

Apply force to one end of a rod in space: why not purely translational? [duplicate]

Why does applying force to a rod in space (or any other isolated systems) on one end leads to both translational and rotational motion? Here's my logic: suppose there is a rod in space. We ...
3
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1answer
68 views

What would a star look like that was the most oblate possible?

This question about why is the Sun so spherical and it's corresponding answer made me wonder: If some younger stars that are rotating faster than the sun are more oblate, then how oblate are they? ...
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0answers
51 views

Solving for position of a SO(3) rotating object, given the integrable functions for components of angular velocity along the principle axes

Assuming that you have approximated or solved the Euler's Equations for components of angular velocity along its principal axes of inertia $x$, $y$ and $z$ - i.e. in the coordinate system that is ...
0
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1answer
62 views

Determining the instantaneous axis of rotation [closed]

Given the following image The question states ,a heavy disc with radius R is rolling down hanging on two non-stretched strings wound around the disc very tightly.THe free ends of the strings are ...
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1answer
29 views

Can you explain the dynamic of forces working in the video?

Lifting Against Gravity - Breaking Magic - Discovery Channel In this video, a woman uses Physics, so that it is difficult to lift her off the ground. The explanation that the video gives at the end ...
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2answers
90 views

A Confusion in Rotational Dynamics

I am trying to analyse the following situation using classical mechanical concepts. Consider a a straight rod $AB$ of mass $M$ and length $L$ placed on a frictionless horizontal surface. A force $F$ ...
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1answer
126 views

rotation behavior of spinning discs

If two discs of equal mass and volume are parallel to each other but not touching, share an axle but using magnetics do not touch it, are not under gravity, and begin to rotate in opposite directions ...
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0answers
46 views

How can I approximate Jacobian Elliptic Functions in terms of basic integrable functions for the SO(3) rotation of a rigid body?

So, the rotation of a 3d body can be described with Euler's equations of motion giving the rotational velocity in components along the principal axes of inertia. As showed in f.ex. this paper, ...