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

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6
votes
2answers
136 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
54 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
vote
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
26 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
votes
1answer
34 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
votes
2answers
31 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 ...
0
votes
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
votes
1answer
42 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 ...
2
votes
3answers
117 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 released ...
0
votes
0answers
26 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. ...
1
vote
1answer
47 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 ...
0
votes
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 ...
1
vote
1answer
24 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
votes
2answers
72 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 part ...
0
votes
1answer
32 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
votes
3answers
51 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 ...
0
votes
0answers
37 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 ...
1
vote
1answer
44 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 ...
1
vote
3answers
77 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. ...
4
votes
0answers
64 views

Gimbal Lock: why is it a problem?

I was watching this video http://www.youtube.com/watch?v=rrUCBOlJdt4 about the gimbal lock problem. I understood that during rotations it could happen that one DOF disappear. Looking at the middle ...
2
votes
1answer
111 views
1
vote
2answers
52 views

What is the purpose of the directions for vector quantities such as angular velocity and torque?

Looking at just both angular velocity and torque, many other exhibit this same property. What is the purpose of and usefulness of having a direction that is in the Z-direction? (assuming that, in the ...
0
votes
1answer
66 views

Understanding work with rotational momentum/moment of inertia

Apologies for the basic question but between the vectors and the spinning, I'm getting confused. If I have a wheel with moment of inertia $I$ spinning at some rate $\vec\omega$ around an axis, what ...
1
vote
2answers
339 views

Is this simulation following real physics?

I am trying to simulate a game in Box2D(Physics engine). The game that I am trying to simulate is very simple and can be found here: http://www.makaimedia.com/#/speartoss What I want to know is that, ...
0
votes
1answer
68 views

Find the acceleration of the bead [closed]

Two identical, uniform large rings, each of mass $\text{m}$ are connected through a bead of same mass, which can move freely. When bead is released, it starts sliding down. The large rings roll over a ...
1
vote
1answer
124 views

Disk and Ball on a smooth surface [closed]

A uniform disk of mass $\text{2m}$ and radius $\text{R}$ is placed freely on a smooth surface as shown in the figure. A particle of mass $\text{m}$ is connected to the circumference of the disc with a ...
3
votes
2answers
91 views

Could 1 force cause a pure moment?

A friend of mine told me if there is only one force, it cannot cause only rotation. I wasn't convinced so I proposed a thought experiment, and now we are both confused. Suppose that we put a rod ( ...
-1
votes
1answer
46 views
0
votes
2answers
3k views

The direction of frictional force in smooth rolling motion

I want to ask about the direction of frictional force in smooth rolling motion which means the rolling object doesn't slide on the surface. Here is the first case, the wheel rolls to the right so the ...
0
votes
0answers
54 views

Finding $\theta$ at any point in time [duplicate]

I am looking to simulate the movement of a steel beam which has a constant mass $m$, and that has a pivot $O$ at one end that is moving with a constant horizontal velocity with magnitude $v$. ...
2
votes
4answers
213 views

Why does Torque exist?

Specifically, why does force increase with the moment arm? What about making a perpendicular force farther away from the axis of rotation increases it? How does the moment arm cause that?
1
vote
1answer
51 views

How to explain gyroscopic precession in a more intuitional way?

When Studying the phenomenon of precession a classic example installation is this: a wheel spins around the Y axis, gravity applies and the upper part starts spinning around the Z axis. The textbook ...
1
vote
2answers
83 views

Why does a rolling disc topple less easily than a standing one?

If a force is applied perpendicular to the surface of a disc it topples sideways. Also, a stationary disc topples more easily than a rolling one. The explanations I've seen for this state that since ...
1
vote
2answers
90 views

Why does a ball eventually stop?

I was wondering, if the force of friction with the ground does not make any work on the ball and just give it the necessary torque to rotate (hence the consideration of static friction coefficient in ...
5
votes
3answers
635 views

Thrust center in space

I have this dilemma: Suppose you have a space ship somewhere in deep space, where there is no drag force or substantial gravity. If the ship has a single engine situated in such a way that the center ...
0
votes
1answer
42 views

Conservation of Angular Momentum for an Object Not Rotating

I have a point mass connected to a string with negligible mass. The point mass has mass $m$ and is moving at a velocity $V$. The string is of length $r$, and it is keeping the point mass tied to a ...
0
votes
3answers
57 views

Axis of rotation and rotating rigid body [closed]

We know that angular momentum of a solid disk rotating with angular velocity $\omega$ is given by $I\omega$ about its center. Now if I chose any axis (parallel to above), will it have same magnitude ...
4
votes
3answers
79 views

How do I find the relation between the accelerations of the ring and the disc (see image)? [closed]

What is the relation between the accelerations of the ring and the disc (see image)? Both the ring and the disc have mass $M$. The ring has a radius $R$ and disc has radius $2R$. They are connected ...
-2
votes
1answer
32 views

Newton's 2nd law for rotation (accelerated rolling and inertial frame of reference) [duplicate]

I need help in understanding why, in accelerated rolling, the center of mass must be at the origin of an inertial frame of reference in order for the second law to be applicable. Thanks!
1
vote
3answers
460 views

Trajectory of rolling billiard ball after collision with another billiard ball with same mass

So, according to this article http://www.real-world-physics-problems.com/physics-of-billiards.html , the trajectory of white (cue) ball is always perpendicular to the line connecting center of ball A ...
0
votes
0answers
75 views

Euler's equations (rotating frames)

I'm trying to understand the Euler's equations and I'm having problems with rotating frames and on which specific frame is each quantity measured. On the equation $$ \left(\frac{dL}{dt}\right)_{...
1
vote
2answers
103 views

Centripetal force: if radius decreases, does ANGULAR or TANGENTIAL velocity change?

Having conceptual trouble with this aspect of centripetal force. Say we have a puck on a frictionless table attached to a string that I am holding through a small hole, so that the puck moves in a ...
1
vote
1answer
63 views

What is the speed of the skaters in this case? [closed]

You're choreographing your school's annual ice show. You call for eight 60kg skaters to join hands and skate side by side in a line extending 12m. The skater at one end is to stop abruptly, so the ...
0
votes
2answers
32 views

How to calculate the acceleration, if the mass-center is not on the force-vector's line (2D)

In a 2D plane there is an object, whose center of mass is at the $P$ point. The mass of the object is $m$. We apply a force $\vec F$ at the point $A$. If the center of mass is on the line, defined ...
1
vote
2answers
81 views

Angular momentum of rolling sphere [closed]

A sphere of uniform density $\rho$ and radius $r$ is rolling without slipping on a perfectly flat surface. It is moving in a perfectly straight line and its axis of rotation is parallel to the plane ...
1
vote
5answers
118 views

Rolling without slipping taking the contact point as pivot

I'm confused about this "rolling without slipping" kind of situation. Or better in this case the object is rolling and slipping, just use the label "rolling without slipping" to identify the kind of ...
0
votes
1answer
35 views

Freebody diagram for an object rolling up a frictionless incline?

I am confused about the direction of the force that causes the ball to come to rest once it reaches maximum height for a ball rolling up a frictionless incline. I understand that the translational ...
0
votes
1answer
33 views

Pulley inertia momentum of inertia

Considering a pulley with some mass, or some friction, How can its inertia (or momentum of inertia) influence the tension on 1 rope? Which part of the rope is influenced? Before or after the pulley?
1
vote
1answer
33 views

Conservation of momentum (angular and translational) [closed]

A ring of radius $R$ and mass $M$ lies on its side on a frictionless table. A bug of mass $m$ rests on the ring. The bug starts walking on the ring with constant speed $v$ relative to the ring. ...
0
votes
1answer
38 views

Strength of the centrifugal force

Let's say you're on a roundabout. When you're radially further away from the roundabout would you feel more centrifugal force or less? I feel like intuitively you'd feel less, but from the actual ...