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

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3
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1answer
102 views

Understanding gyroscopes

Considering the typical situation of a rotating bicycle wheel held by one end of its axle by a rope tied to the ceiling: gravity torque is the time derivative of the angular momentum, and in this case ...
2
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1answer
131 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 ...
1
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1answer
42 views

Attaching a long rope to the Moon to travel around the Earth

Suppose we were to attach one end of a very long and strong rope to the Moon. Provided that I were to have a device that would allow me to shorten/lengthen the rope to accommodate for differences in ...
1
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1answer
79 views

Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
1
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1answer
117 views

Molecular rotation - Energy levels for an asymmetric molecule

For a molecule with spherical symmetry, the energy level of rotation for quantum number $J$ is: $$E(J)=\frac{J(J+1)\hbar^2}{8\pi^{2}I}$$ "$I$" is the Moment of inertia for the molecule ...
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1answer
456 views

Back motor effect of loaded generators?

The back motor effect (see Counter-electromotive force) is the counter torque which opposes the rotational motion of the coils in a generator when the generator is under load. The back motor effect ...
1
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1answer
836 views

Equivalence between a charged rotating cylinder and a solenoid

Suppose we have a cylindrical shell of radius $r$ with surface charge density $\sigma$. Then we start rotating the cylinder at an angular speed $\Omega$. You can show that in this case the surface ...
0
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1answer
24 views

Calculating the components of angular momentum of a rigid body

You have a rigid body with 1 fixed point in space (the origin). It's self-explanatory how to get the following equation for the angular momentum: $\vec L = \sum_n m_n\vec r_n\times\vec v_n$ ...
3
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0answers
59 views

Why does the video recorded by a falling, rotating camera seem to stabilize?

Here is a video of a GoPro falling from a plane: http://www.youtube.com/watch?v=QrxPuk0JefA Any idea what is happening when the image "stabilizes" around 0:35? I think it is because the camera's ...
3
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0answers
113 views

3 Axis Gryroscope with forced Precession and Limits of Motion

I am working a problem concerning a 3 axis gryoscope, the spinning mass is a magnet (dipole). This is part of a optical sensing device. The inner gimbal is for pitch rotation, and the outer gimbal is ...
3
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0answers
105 views

Videos of changing the orientation of an astronaut in space

Kane, Headrick and Yatteau describe in their paper "Experimental investigation of an astronaut maneuvering scheme" possible maneuvers to change the orientation in space without external torque. Is ...
2
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0answers
59 views

Difference of the O(N) Non-linear Sigma model and SO(N) Non-linearSigma model

The Hamiltonian \begin{equation} H=J\sum_{i,j}\vec{n}_i\cdot\vec{n}_j \end{equation} is invariant under a global rotation $\vec{n}_i\rightarrow R\vec{n}_i$, where $\vec{n}$ is a $N$ component rotor ...
2
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0answers
157 views

Push a box in a plane with friction. How to deal with the rotation?

Suppose I have a box (say, length-1m, width-1m, height-0.5m) on the plane with friction. I can apply a horizontal force in on the surface of the box. If the force doesn't pass through the center of ...
2
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0answers
39 views

Computing Latitude Given Quiescent Gyroscope Data

Suppose I place a gyroscope in a theoretically perfectly quiescent, closed room. Let its output be given as a vector ${\bf v} = (v_x, v_y, v_z)$ indicating rate of rotation around three orthogonal ...
2
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0answers
484 views

Why does a coin falls faster when it's flipping as well?

From my experiments with measuring how fast a coin falls, I have consistently measured a faster falling rate for a coin that flips as it falls. As an example, a coin dropping on its edge from height ...
2
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0answers
1k views

Forces and torques about the CENTER OF MASS of a physical pendulum

I'm currently stumped by the following situation. Say we've got a rectangular physical pendulum (think ruler with a hole-punch at one end). It's trivial to analyze the motion of the pendulum with the ...
2
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0answers
228 views

Why do control moment gyroscopes exhibit “torque amplification”?

There are a number of articles that describe the benefits of using control moment gyroscopes (CMGs) over reaction wheels in inertial navigation applications. One of the primary benefits of using a CMG ...
2
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0answers
256 views

Levitation rotation speed involving laser acceleration, pyrolytic graphite and a vacuum

The experment would involve a small NIB magnet levitating between or on the diamagnetic material pyrolytic graphite, unlike other forms of levitation this doesn't require power to run such as ...
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0answers
32 views

Deriving tensor in Euler's equations for rigid body rotation

The answer to physics.stackexchange.com/questions/104513 gives the following derivation of tensor $I$: $\begin{align} \frac{\text{d}}{\text{d}t} I &= \frac{\text{d}}{\text{d}t} ...
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0answers
45 views

A rigid rotating rod that breaks in two pieces

Suppose we have a rigid rod of lenght $L$ and homegenous mass density. One of its extreme points, say $P$, is fixed so that the rod can rotate around the axis passing in it. Initially the rod is held ...
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0answers
55 views

Why does pitch in a helicopter take effect 90 degrees later?

In a helicopter if you want to give it a forward pitch, you change the angle of the blades when it is in this position ---- So the two blades experience unequal lift and because o gyroscopic ...
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0answers
67 views

Restrained double pendulum

The equations of motion of a double pendulum are well-known. Usually you'd have the them expressed in the rotations $\theta_1(t)$ and $\theta_2(t)$. There are two degrees of freedom. Now consider the ...
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0answers
60 views

Rotation motion like the number 8

I'm a college student majoring in culinology and I'm trying to find out the reason or method of the number 8 motion. Responses doesn't have to be in culinology examples, but that would be a great help ...
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0answers
51 views

Is there any role of steering in turning?

I am aware of the practical requirement of turning the steering wheel to turn a car while going on a straight and even curved road. But in the proofs of turning of car on leveled or banked curves, ...
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0answers
228 views

Degeneracy in molecular rotation energy levels for asymmetric molecules

I was recently reading Atkins' Physical Chemistry, the topic of rotational energies of molecules. It states the degeneracies of spherical top, symmetric and linear molecules as being $(2J+1)^2$, ...
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0answers
87 views

Seeking help simplifying this EOM equation

I am working on solving the equation of motion for a particular system. It has been a long time since I've worked with matrix equations and need help in simplifying the following: ...
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0answers
315 views

Moment of inertia about a tilted axis

I apologize if it seems foolish, I am a beginner. Suppose I am given an object, whose moment of inertia along the x,z axes are known. Suppose it rotates around a tilted axis, ...
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0answers
574 views

Magnetic field of solenoid in cone shape

I have done some drawings of the magnetic fields of cone shaped solenoid electromagnets. I based this on the work of Tesla and some explanations of Bashar, known as the Bashar Cones. I found very ...
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0answers
90 views

Why does angular velocity lies in the axis passing through the center of the circumference?

I understand that it can't be placed anywhere on the radius because it doesn't vary with it ( and so of course it doens't make sense to place it anywhere else on the plane), but why do we place it ...
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0answers
189 views

Limitations on the choice of axis of rotation regarding rolling wheels

Consider a situation where a wheel is rolling without friction on a level surface. Call the center of the wheel $C$, the point where the wheel contacts the ground $G$, and some arbitrary other point ...
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0answers
638 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. ...
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0answers
54 views

Fading transition and rotation of and object in 2D

I'm looking for sources about I guess dynamics subject. The model I'd like to solve is reduced to a question of: How does a force applied on a certain point of an object results in both fading ...
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0answers
367 views

How equivalent are heat energy and work energy in connection with a spinning flywheel?

Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper. Now we apply some heat energy at the center point of flywheel A, causing it to slow down a ...
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0answers
249 views

How to model an accelerometer measurements on a car wheel?

I am working on kinematically modelling an accelerometer on a car wheel. When working on the initial conditions, I am confused whether or not I should use the gravitational acceleration since there ...
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0answers
384 views

Should angular momentum change or it should not.?

Let us consider a body with an arbitrary shape. Let its center of mass be assigned coordinates (o,o,z) with respect to an origin.Now let us consider two equal and opposite forces acting on the body ...
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0answers
40 views

Does a rotating plank only acquire rotational kinetic energy?

I have another doubt with a Kleppner problem :(. A thin plank of mass M and length l is pivoted at one end. The plank is released at 60$^{\circ}$ from the vertical. What is the magnitude and ...
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0answers
19 views

How do two rigid bodies with different 3rd moment of inertia rotate differently?

If rigid bodies $R_1$ and $R_2$ has exactly same total mass $M$, central of mass, and rotational inertia $I$, but different third moment of inertia $M_3$, how would they move/rotate differently? ...
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0answers
48 views

Illustrate the transition from linear to rotational kinetic energy

I wish to find an everyday situation that illustrates the following: A rod is moving in a direction perpendicular to its axis. One end "gets caught" and the rod starts rotating around this end. THE ...
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0answers
24 views

rotation of earth and changes in its diameter

could calculated the changes of the Earth's diameter cause the rotation?? I have seen 2 other posts about it but I couldn't understand their calculation and they were a little confusing and couldn't ...
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0answers
14 views

Pseudo force in rotational motion?

If a cylinder is in combined rotation and translation on a moving surface(say a plank with some acceleration), while solving for the acceleration of the centre of mass of the cylinder, do we consider ...
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0answers
36 views

Rotating and moving reference frame

I've looked through your forums and can't find exactly what I need. I have a two objects whos dynamics can be described in discrete time as follows: $x_A(k+1) = x_A(k) + ...
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0answers
64 views

Imagine a 50-mile tower spanning from desert floor to the Karman Line

CORRECTION: The structure weighs 1.568E15 kg.s Does the structure effect the equilibrium of earth's rotation? Would momentum from Earth's rotation apply lateral force to the structure? What else do ...
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0answers
22 views

model for flexible stick

I'm trying to model a flexible stick with a partial differential equation. I want one of the ends to be fixed and the other end to swing. Do you guys know of any good models I can use? Any ...
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0answers
317 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 ...
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0answers
60 views

Terminal velocity for rotating system

Suppose we have a small bob/ball attached via rigid rod to a pivot in a viscous medium and then rotated by a constant torque, will the system finally(after considerable time) rotate with constant ...
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0answers
67 views

Total energy of a rotating body?

I've no problems with the first part. However, I'm struggling with the last part of the question. The first thing I did is to find the a new moment of inertia for the whole system including the ...
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0answers
58 views

Two disks on frictionless surface, demonstration

Consider a system composed of two plane disks, which we will designate as $D$ and $d$. Their radii are $R$ and $r$ respectively $(R>r)$. The disk $d$ is fixed over the disk $D$ and a ...
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0answers
65 views

Gravitational Behavior of Rotating Body

Consider a stick with a (ball-shaped) weight at the end of it. Let's say this stick is in a state of rotation (it's floating in vacuum) and is also in a state of translational motion. Consider a ...
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0answers
45 views

what happens to the angular velocity of star in star-black hole system?

What happens to the rotational and revolutionary angular velocities of star in star-black hole system as the star loses mass ?
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0answers
201 views

Dose the gravitational force produces precession in the spinning top?

I'm new at classical mechanics but the text book says there is the torque in the spinning top which generated only by gravitation. It is hard to explain the situation, I've add the link. ...