# Tagged Questions

A tag for questions about rotational motion, including angular velocity and angular acceleration.

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### Rotation, translation or both. [closed]

the square is the same material throughout, equal mass distribution. In this case, will the object rotate, translate or both and why ? Thank you.
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### Calculating moment of inertia for a cylinder?

I'm trying to calculate the moment of inertia for a cylinder about a longitudinal axis, but I don't know where I went wrong with my approach. $$I=\int r^2 dm$$ Assuming constant density: \frac{M}...
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### Correct formulas for two wheeled robot motion

I'm trying to write a simulation of a two wheeled robot, which can be controlled by varying the speeds of his wheels, independently. However, the physics engine that I'm using can only rotate a body ...
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### If the earth is spinning and we are spinning with the earth, why doesn't it take longer to go opposite the rotation?

Imagine you are on a walking type platform at an airport where you are walking with the platform where it moves you faster walking with......than against. This would be the same concept as if we were ...
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### Getting an object to travel at or near light speed by adding velocities [duplicate]

Firstly I'll just give a brief example of where my query came from. I was watching the episode of Futurama where Bender meets God after being fired from the planet express ships torpedo tube. The crew ...
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### Why direction of angular velocity is taken along the rotational axis?

I read that it is a convention. But what does that mean in physics? If it would have been a sign assigning matter, I could confess but what convention means here? When we decide the direction of ...
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### Is angular velocity parallel to axis of rotation?

I'm reading the Wikipedia page on angular velocity. It says here of the angular velocity vector in three dimensions that “[t]he magnitude is the angular speed, and the direction describes the axis of ...
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### How far does the ball travel before pure rolling motion occurs? [closed]

A bowling ball is given an initial speed $V_o = 10 \text{m/s}$ on an alley such that it initially slides without rolling. The coefficient of friction between the ball and the alley is $\mu = 0.06$. ...
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### Expressing 3D orientation in alternative to Euler angles for 3D rigid body dynamics

I was unsure whether it would be best to post this in Physics, Maths, or other forums, so please say if this question is suited better elsewhere. I am trying trying to create a physics engine for a ...
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### How are these marbles being accelerated?

This question refers to an effect visible starting at around 5m45s in this video1. (The question will make little sense if one has not first watched the clip.) The observation At around 5m45s we ...
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### In golf, is there a rotational mechanical advantage of using a thicker grip?

I was asked to migrate this question to the physics exchange. Ok, so many professionals are now using the new SuperStroke golf grips. I am basically thinking about the concept of a bigger grip, but ...
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### Force required to rotate a rod around an axis [closed]

The problem I'm trying to solve is: How much force, momentarily applied to the rod, is required to rotate it around an axis by a given degree? Assuming there is friction applied at the axis (...
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### What is the effect of torque transmitted through a gear system to the angular acceleration of a flywheel?

For a school project, I am trying to design a system that will spin a flywheel at a high rpm to store energy. My initial idea was to accelerate the flywheel via a compound gear train with an ...
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### Alternate Formulation of Kinetic Energy for Lagrangian

So I have a question regarding this system: It is supposed to be a simple model of an aircraft with the fuselage idealized as a concentrated mass $M_0$ and the wings modeled as rigid bars carrying ...
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### Find the Kinematic degrees of freedom of the following contraption

In the above mechanism it is required to find the generalized coordinates to write equation of motion of the MDOF system. I just want to ask how do we actually approach such a problem? How to identify ...
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### motion in the body-fixed frame?

This is really basic, I'm sure: For rigid body motion, Euler's equations refer to $L_i$ and $\omega_i$ as measured in the fixed-body frame. But that frame is just that: fixed in the body. So how ...
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### Rotation with axle with unequally sized wheels

https://youtu.be/hwgjMPaKMiA In the above video, I have an assembly of two wheels of unequal radii connected via an axle. Now when we apply an external force anywhere on the axle, we see something ...
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### Comet's distance with and without gravity [closed]

I've got this question that I just can't seem to answer. The question is as follows: A comet approaches the solar system with velocity v and would, if the sun would not attract the comet, pass the ...
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### How does a cyclist moves the center of mass of the cycle-cyclist system?

Consider the image shown below, In the left diagram the centre of mass of the system lies upon the perpendicular from the point of contact. But in the right diagram the centre of mass has shifted ...
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### Example where angular momentum and angular velocity are not parallel

I am unable to visualize any case where angular momentum and angular velocity of an object are not parallel.
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### Why do linear momentum and angular momentum have to be conserved in ground frame only?

According the Newton's second law of translational and rotational motion respectively if the net external force /torque acting on a body is zero then the linear/angluar momentum is a constant . So ...
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### Physics related derivation of equation of cycloid

So I was trying to find the path traversed by a point on the rim of a rolling disc. I eventually landed up at an equation but when I went to check it out in the internet, I couldn't find any similar ...
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### Simplified rolling tire problem - hollow shell vs solid?

First off, I don't understand the math formatting thing on here, but none of these formulae are too complicated. Take a tire rolling down a hill with angle t and distance d. Modeling it as a hollow ...
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### Speed of a point on a concentric disk setup

I have been really solving this question that my friend and I had thought of while discussing about speed of light. Imagine there is a set-up where there is a light source that is surrounded by a ...
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### Gear ratio in bicycles using rotational motion

When we change the gears of the bicycle we are riding, we change the the disc we are currently at (which are located at the place where we pedal) to some other disc. This means the radius of the ...
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### 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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### Kinematics of Euler angles relative to a rotating frame

I have a rotating body $B$ and a rotating frame $F$ whose orientations are described by the quaternions $q_B$ and $q_F$ respectively. I also have the angular velocity vectors $\omega_B$ and $\omega_F$....
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### 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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### Deriving some uniform circular motion equations

My question basically boils down to this. How do we derive these relationships. 1.)What is the relationship between radius and centripetal force? (inverse, but why?) 2.)What is the relationship ...
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### 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 86400....
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### Intuition for why friction on rolling objects is in the same direction as motion?

When we usually draw friction, it is opposite the direction of motion. However, in rotational motion problem when a cylinder is rolling on the floor, it is in the same direction as the motion. I did ...
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### How would the angular velocity of the rod change if it slipped on the table?

I wanted to consider a second case of my homework assignment. We were asked to solve the question: A uniform rod of length b stands vertically upright on a horizontal plane in a position of unstable ...
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### 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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### What are the Kinematics of an Irregular Tripod?

It is a common maxim (at least within the Scouting community) that a triangle is the most stable shape. In practice this means structures should have three legs whenever possible, and have cross-bars ...
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### On application of angular momentum conservation laws

Consider a situation like this: a massless ring is kept fixed at rest on a horizontal plane. A massless thin string attached at its one end to a point on the circumference of the ring while its other ...
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### Can a pair of members of a “rotating system” be characterized by one value of displacement magnitude?

There seems to be a claim (cmp. Goldstein, "Classical Mechanics", eq. (4-126); or also perceptable here) that values of "velocity", and of "speed", of some participant, say $P$, can not only be ...
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### Finding Angular Acceleration of rod given radius and angle

A uniform rod is 2.0 m long. The rod is pivoted about a horizontal, frictionless pin through one end. The rod is released from rest at an angle of 30° above the horizontal. What is the angular ...
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### Frames of Reference in a Rotational System

Imagine two concentric rings with different diameters. One is spinning within the other. There is a small gap between the outer diameter of the inner ring and the inner diameter of outer ring. From ...
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### 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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### Unruh radiation in a rotating frame

Unruh radiation normally applies to linearly accelerated frames Is there an equivalent of the Unruh thermal radiation in a frame that is spinning? I am not aware of any horizon being created from a ...
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### Power exerted by the contact force on a wheel slipping without rolling?

I was taking an old (2008) Mechanics of materials examination, and the system is a sphere on a half circular motionless rail. We first study the motion of the sphere in the case of rolling without ...