# rotational-dynamics's questions - English 1answer

1.724 rotational-dynamics questions.

### Torque exercise problem

I am learning physics with help of this site https://www.khanacademy.org/ And I have stumbled upon a task that I can not completely understand The task says: A gasoline engine producing Nm of ...

### 1 Linear momentum conservation for interaction between rigid body and point mass

Let's say I have an interaction potential between a rigid body and a point mass expressed in spherical coordinate : $V=V(r,\theta, \phi)$. The coordinates $r, \theta$ and $\phi$ specify the position ...

### 1 When a force is applied on a body, which point does the body rotate around?

I understand when a force is applied to a body it causes moments on all points not lying on the force's line of action. So which of these points acts as the pivot point around which the body actually ...

### 5 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 ...

### 1 Equivalent inertia at spherical joint in multibody tree

Consider a tree system of rigid bodies and spherical joints. Starting at an outermost body, I'd like to calculate its equivalent mass (which I'm guessing would be an inertial tensor or something) at ...

### 2 Can I avoid spaghettification with a spin?

I am aware of spaghettification effect caused by entering a black hole, as well as fundamental physics of an object in space, so here is my theoretical construct: if I place an object in space where ...

### Angular momentum in Rotating Frame for satellites

I am working on satellite orbit propagator, I am propagating the satellite position and velocity in the inertial and rotating frames. To validate my propagator, I am checking the angular momentum and ...

### 12 Why does a car engine not do work if the wheels don't slip?

I saw this mind boggling result that if the tires don't slip then the work done by an engine to move a car is zero. Why is this true? Moreover, what does this truly mean? Update: Sorry about not ...

### 1 Rotation matrix help [on hold]

1 answers, 104 views rotational-dynamics vectors
So I am doing some exercises in Susan Lea's book Mathematics for Physicists, currently question 7 chapter 1: Find the matrix that represents the transformation obtained by (a) rotating about the x-...

### 2 What is the problem of having an inertia tensor not satisfying the triangle inequality?

It is well known that rigid body inertia tensors are 3 by 3 positive semidefinite matrices, which is the same as saying that their eigenvalues are all non-negative. A little less known is the fact ...

### 1 A hemisphere rotating on a flat surface ends up on the flat side. Why?

0 answers, 33 views rotational-dynamics rotation
So I was playing with my kid and this wooden half Kiwi (radius about 20 to 25 mm) got my attention: What I noticed was, when I give it a spin on its pointy end and if a certain initial speed of ...

### How does Earth's rotation affect long range shooting trajectory? (Coriolis and Eötvös effects)

I know that this has been a well discussed topic on the internet and I read a lot about it, and yet, I still have some doubts. I'm talking about Coriolis and Eötvös effect. Let's start with Coriolis ...

### -2 Gyroscope calculation [on hold]

Is it possible to calculate rpm of a gyroscope based on the mass of a gyroscope and the force that acted on it? Let say the mass of the gyroscope is 1 kg, and the force is 5 torque. Is there any ...

### Can a wall exert a force at an angle? Beam in rotational and static equilibrium problem

The answer is C. I'm thoroughly confused! The question is asking for when the magnitude of the vertical component of the force that the wall exerts on the left end of the beam is the smallest. How ...

### 23 Rotation angle of a giant water lily when a child crawls on its rim

Below is a picture of Giant Water Lily. Scientific Name: Victoria Amazonica. Leaves of some of these could be as big as 3 m diameter and carry a weight of 45kg spread evenly and can support a child. ...

### A lever arm-definition question

2 answers, 903 views rotational-dynamics torque
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. ...

### 3 Why do we have to take torque due to pseudo force for an accelerating axis?

For e.g. Here, A,B are strings. A was cut. The rod is of length l. Acceleration of center of mass = a and angular acceleration of the rod is alpha. Now if I want to find the net torque about the ...

### Rolling without slipping and friction [duplicate]

When a ball rolling without slipping along an inclined plane reaches the bottom, it has a linear velocity $v$ and angular velocity $\omega\ =v/r$ at the bottom. Then it continues its motion on the ...

### -1 Dynamic question [closed]

In a welcome triumph of technology, Canada shoots its three federal party leaders far into space.Scheeridan, TrustDuh, and SingASong have identical masses of 80.0 kg and they are tied together with ...

### 1 How does a cilinder that rolls without slipping lose energy? [duplicate]

Suppose a cilinder that rolls without slipping on a horizontal rough surface. The slipping is prevented by friction, which therefore slows it down, so it loses kinetic energy. But no dissipative work ...

### -1 Calculating breaking rpm/force of a spinning ring [closed]

Let's suppose I have a ring of mass m, and radii r, thickness t, and width w, as shown: I would like to come up with a way to be able to work out the highest RPM a ring can reach given m, r, t and w, ...

### 4 Sum of energy for 2 solids in rotation

I would like to compute the sum of energy of the following case: Two solids are turning (disks). Yellow solid is turning at $w_1$ radians per second around its center of gravity and blue solid is ...

### -2 Confusions about rotational dynamics and centripetal force

I am a high school student. I am having confusions about the centripetal force and rotational motion. I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...

### 1 How can a particle in circular motion be in translational motion?

2 answers, 353 views rotational-dynamics angular-velocity
I came across this: If a particle is moving in a circle it is in pure rotational motion about the centre of the circle, while for a moment it may be in pure translational motion about some other ...

### 3 Precession on a heavy rod: Angular momentum and torque contradiction

Say I got a so massive rod and a relatively light spinning flywheel. Fixing an end on a pivot, and the disk on the other endpoint, as expected, the rod would undergo precession. If we call the plane ...

### 7 General motion of a cone on an inclined surface

Suppose that a solid cone is placed horizontally on an inclined surface and is initially at rest. How will the cone move when it starts motion due to its weight? I know that its motion depends on the ...

### -2 What is the meaning of angular momentum about a point? [closed]

Angular momentum is always calculated about an axis and not about a point( according to me). I have a scenario on this topic. In the image below it is asked to calculate angular momentum about origin....

### 38 Can a Foucault pendulum really prove Earth is rotating?

According to this article, a Foucault pendulum proved Earth was rotating. I'm not sure it really proved it. If Earth weren't rotating and a Foucault pendulum started in a state with zero velocity, it ...

### 3 Start of gyroscopic precession

Let's consider the classical example, the wheel hung by one side of the axle: ¹ When the wheel is not spinning, it will tilt down the free end of the axle first. When the wheel is spinning, it will ...

### 3 Lagrangian of rotating springs

I'm trying to construct the Lagrangian for the following scenario. A turntable of radius $R$ is rotating at angular velocity $\omega$, maintained by a motor. Two springs with Hooke's constant $k$ are ...

### Moment of inertia of a Rod

Imagine a rod inclined like a ladder, to the left, touching a wall. Say, the wall is the Z axis, and the "ladder" is the rod. I want to know how we can calculate the moment of inertia of the rod ...

### 1 How is it possible to calculate the moment of inertia?

I would like to calculate the angular acceleration of an object on which a force $F$ is applied at point $P$. The scene is 2D, and the complex object consists of many axis-aligned rectangles. I ...

### Tethered ball - Centripetal force

I'm learning physics on Khan academy and i have stumbled upon a task that I cant completely understand and I'm a type of person that cant continue the studying until everything that I have read is ...

### 1 Proof of holonomic constraints for a wheel on a track

I'm faceing a problem of a thin wheel of radius R rolling without slipping on a track (y = f(x); on xy-plan). The wheel plane stays vertical and tangent to the track at the contact point P. $\alpha$ ...

### Gyroscopic precession - Angular momentum in vertical direction

In the classic example of gyroscopic precession, the wheel starts to process, and now acquires a angular moment also in the vertical direction. Initial angular momentum was in a single plane. The one ...

### How does precession affect angular momentum?

I have been studying Irodov's problem book. There are a lot of good problems that challenge conceptual knowledge, and so I have to ask somebody for a qualitative answer. I can best describe my ...

### Matrix Euler’s rigid-body equation

Define the action $$S[g]=\displaystyle\frac{1}{2}\int^1_0 Tr(I(g^{-1}\dot g)~g^{-1}\dot g)~dt.$$ $I:SO(N)\to SO(N)$ denotes the endomorphism $\omega \to I(\omega)$ with \$I(\omega)_{ij}=\omega_{ij}/...

### Comparison between Euler angles and Rodrigues rotation formula under small rotation hypothesis

Sorry for boring you during summer vacation, my friends. I am haunted by the comparison between Euler angles and Rodrigues rotation formula under the small rotation hypothesis. Maybe, they cannot be ...