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

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1
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1answer
39 views

An impulse is given to a sphere out of the center?

I'm wondering what will happen if there is an impulse $J$ given to a sphere mass $M$ out of its center? I'm sure that it will rotate about the center, but what is its translational motion? It will ...
1
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1answer
34 views

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 ...
3
votes
2answers
70 views

Intuitive explanation of rotational inertia with respect to angular momentum

I understand that there are proofs (e.g. proof, another proof) of why the angular momentum about two points for an object is the same. However, could someone give an intuitive explanation of why this ...
1
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4answers
136 views

Spinning disk touches stationary disk [closed]

Suppose we have a solid disk of mass $M$ and radius $R$ that is spinning at an angular velocity of $\omega_0$ about an axis going out its cm. It is brought to touch a stationary disk of mass $m$ and ...
3
votes
1answer
514 views

Find angular momentum about any point

How do I find the angular momentum of a body about any point? We know that $L=I\omega$ for a body rotating in space, where $L$ denotes the angular momentum, $I$ denotes the moment of inertia and ...
1
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1answer
471 views

Independence of angular momentum with respect to origin for rotation about center of mass

Why is angular momentum for rotation about the center of mass independent of origin of the coordinate system?
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2answers
148 views

Angular momentum in rotational motion

Ok so there are two things that have completely confused me- things related to angular momentum. 1.)First of all, how can a body possess angular momentum even though it is not rotating? According to ...
0
votes
1answer
66 views

A mass in a rotating tube

A mass rotates on a horizontal surface inside a frictionless hollow tube with a angular velocity omega. The only force acting on it is a force N with which the tube pushes the mass. It is expected ...
2
votes
1answer
51 views

Toppling Of an Object [closed]

I did not understand the following steps regarding calculation of minimum force F required to topple object about point A. Total Torque = Fb - mga/2 If torque>0 then body topples. What i did not ...
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2answers
58 views

Time dependent ODE involving cross product

Let $\vec{A}$ be any time dependent vector quantity, and $\vec{\alpha}$ any constant vector. I was told that a solution to the differential equation $$ \dot{\vec{A}} = \vec{\alpha}\times\vec{A} $$ is ...
1
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1answer
64 views

To prove uniqueness of Rotation Tensor [closed]

How can you prove that a rotation tensor which rotates some given vector is a unique tensor? Let's say we have a vector 'a' and we take a tensor product of that vector with some tensor 'Z' such that: ...
1
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1answer
37 views

Is this equation for the rotational weight of a half disk correct? [closed]

I need to know what rotational force the weight of this disk applies to the axle. I'm not sure what the units are, whether it's torque or something else I'm looking for. The weight of the disk is ...
0
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2answers
55 views

Why does an ice hockey stick, when thrown on ice always rotate and translate together before coming to rest? Why not only rotate or only translate?

When a hockey stick is thrown on ice it simultaneously rotates and translates before stopping. Friction probably plays the main role here, along with the shape of the stick. I think maybe it is due to ...
0
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2answers
54 views

Moment of inertia of a body

I found the relation,$I=2\cdot T_\text{rot}$, where $I$ is the moment of inertia and $T_\text{rot}$ is the kinetic energy of rotation. Does moment of inertia depend on angular velocity? If it depends, ...
1
vote
1answer
57 views

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

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 ...
0
votes
2answers
48 views

Cause of centripetal acceleration in a ring

Suppose a ring is rotating in space with an angular velocity $\omega .$ Then each element of the ring is having an acceleration of $m\omega^2 r$ ($r$ is the radius of the ring) but what force is ...
4
votes
1answer
379 views

Why is it difficult to ride a bicycle with a partially inflated or deflated tyre?

It is a common observation that riding a bicycle with an inflated tyre is easier than riding one with a deflated tyre but why is it so? As per my knowledge in an ideal case of no deformation in ...
1
vote
2answers
723 views

How easily can the Earth flip?

The recent media attention to sunspot activity (however warranted) reminds me of a question I had long ago. Given the angular momentum and the slight 'wobble' of the earth, and remembering the ...
0
votes
1answer
44 views

Angular Velocity of Semicircle [closed]

In a 2-Dimensional world, a semicircle with center O, mass M and radius r is placed on the ground, with C as the point of contact. A small beetle of mass $m$ is placed at C which starts walking ...
0
votes
1answer
56 views

Is the angular momentum vector parallel to the rotation axis in this system?

I want to clear up an ambiguity that seems to exist in my textbook. I am told that a rotating body will have an angular momentum vector parallel to the rotation axis only if the rotation axis is ...
3
votes
1answer
61 views

Moment of inertia meaning?

Why is the formula for calculating the moment of inertia this integral $$ \int r^2 dm~? $$ I understand the way we derived this formula from looking at the distribution of kinetic energy of a ...
0
votes
1answer
371 views

Area moment of inertia of regular $n$-gons over polygon center $O$

Is it possible to consider the regular polygons ($n$-gons) as deformed circles and use a pseudo-polar coordinate system to calculate their moment of inertia over its center $O$. Inasmuch as I know (I ...
3
votes
1answer
34 views

Mechanics principle

When two forces of equal magnitude, opposite in direction and parallel act on an object, the object will rotate without having translational speed. On the other hand, when three concurrent forces ...
1
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0answers
86 views

Calculating torque required to keep an object rotating

I am hoping someone can help me clear up my understanding on rotational dynamics. In particular, how to determine the torque required to keep an object rotating. My understanding (please tell me if ...
0
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2answers
179 views

Direction of static friction in inclined rolling motion

I can't seem to understand in which direction static friction faces for inclined plane motion with rolling motion. This considers rolling motion without slipping, how do i find the direction of the ...
9
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4answers
4k views

Hamiltonian is conserved, but is not the total mechanical energy

I wondering about the interpretation for the energy difference between the Hamiltonian and the total mechanical energy for systems where the Hamiltonian is conserved, but it is not equal to the total ...
0
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2answers
42 views

What are our limitations on spinning a baseball sized 5 kg sphere to really fast speeds?

I know the limitation of the ball being able to hold itself together, lets assume that would not be an issue. If we were to apply a constant force over long enough time would anything short of the ...
25
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7answers
3k views

If I toss a coin, vertically, on the surface of Mars, will it land back in my hand?

When I toss a coin in Mars, is the planets atmosphere rare enough that I'd rotate with the planet (at its angular velocity), but not the coin?
2
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0answers
62 views

Man walking on the rotating platform [closed]

The problem is: The solid cylindrical platform with mass $M$ and radius $R$ rotates with angular frequency $\omega$. On the edge of the platform there is a standing man with mass $m$. Then man ...
1
vote
1answer
46 views

Four bar linkage moment transmission

The question is. I know the angular velocity of $d$ after applying dynamic mechanics and the constant angular velocity of $b$ of $2\pi\ \text{rad/s}$ and I know the input moment of the power source ...
1
vote
1answer
65 views

How do I handle elastic contacts in a simulation with friction [closed]

I'm trying to simulate a wheel as it hits the ground. Problem 1 Suppose a disc is dropped from a height. It has initial velocity of $-x,-y$ caused by throwing and gravity. It has no initial angular ...
1
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1answer
107 views

Conservation of angular momentum during rolling

A disk having initial angular velocity $\omega$ is gently placed on a rough horizontal surface. What is the angular velocity of rotation when pure rolling starts? I've tried applying conservation ...
0
votes
0answers
74 views

Simple Rotating frame of reference

I have a car moving in straight line with certain time-varying acceleration and there is another car moving in a curvilinear way along some curved path with some time-varying acceleration. The ...
0
votes
1answer
52 views

Is a rotor balanced at constant angular velocity?

I have an asymmetrical rotating part. It vibrates its housing and emits audible noise. I need to add weights to ensure smooth rotation. However, I am constrained in which regions I can add ...
-1
votes
1answer
31 views

Understanding the constraint of tension with a rigid body

I want to know why doesn't $T_1 = T_2$? I think its probably because of the Pulley but still aren't the Tensions Equal but opposite in direction.
0
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1answer
46 views

A sphere rolling down a plank - an error in calculating its energy

Consider the following situation: A sphere with radius $r$ rolls down a plank which forms an angle $\theta$ with the horizontal axis. The starting hight of the centre of mass is $h$. We assume that ...
1
vote
1answer
94 views

Why does the pen does not move straight?

If i put a pen on a table in its horizontal position and then i try to move it horizontally by giving it a small push, so that it would fall off a table, i expect it to move horizontally but my pen ( ...
7
votes
3answers
791 views

Why don't we talk about angular momentum at all in fluid mechanics?

People usually talk about similar (or maybe not?) things like vorticity or enstrophy in fluid mechanics, but no one talks about angular momentum, why?
0
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2answers
1k views

Tricky conceptual question: ball sliding and rolling down incline [closed]

We all are familiar with the classic ball rolling down the incline exercise in rotational dynamics. Here is quite a tricky conceptual problem: You have an incline of fixed height, but the angle ...
4
votes
1answer
669 views

If a bullet is fired vertically upwards, when it comes back does it fall to the same spot? [duplicate]

What I'm basically asking is that if a body is projected with sufficiently high velocity so that it doesn't escape from the earth's gravitational field but reaches an appreciable height with respect ...
0
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0answers
40 views

A problem regarding translational & rotational motion

Let a force $F$ be applied to a body of mass $m$ for time $dt$ where the line of action passes through the centre of mass. This means that the change in momentum will be $Fdt$, and the change in total ...
2
votes
2answers
2k views

Moment of inertia of a coin [closed]

I have a a coin infinitely thin, rotating along the diameter. How to derive the formula for it's moment of inertia passing through the diameter. I was suggested to use the surface density and ...
0
votes
1answer
122 views

Rotational dynamics

In studying rotational dynamics of a rigid body, I can't seem to understand why you can solve the problem correctly only using certain points in a body and not all? Angular momentum and torque leads ...
0
votes
0answers
46 views

What is the derivation of $r*F=Iα$? [duplicate]

Please give me the derivation of the formula r*F=Iα for extended body. where, F=applied force r=distance between point of rotation & point where force is applied I=moment of inertia of the body ...
0
votes
0answers
33 views

The precession component in the direction of spinning

Is the precession increasing the rotation around the axis of spinning? w = (nutation) i + (precession component) j + (another precession component + spinning) k or to rephrase, is the precession ...
1
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1answer
102 views

Gyroscope precession

I have a system diagrammed and explained in the image below. Experimentally I believe the wheel will rotate around the pivot point where the cable is attached in a counter-clock motion if ...
4
votes
3answers
6k views

Which force makes a wheel roll down the hill? What causes friction?

A wheel rolling down a hill has two axis of rotation. One is where the center or mass is and the other is the point of contact with the surface which acts as a fulcrum. I was trying to understand ...
3
votes
1answer
145 views

Why isn't kinetic energy conserved in this rotational dynamics problem?

Consider a uniform rod which is spinning about an axis that goes through its centre, perpendicular to the rod itself. Two small rings are attached on the rod at equal distances from the centre. As the ...
2
votes
2answers
44 views

The way planets rotate and revolve [duplicate]

Why is that the all planets move in the same plane?(correct me if I'm wrong) Why not some of them in anticlockwise direction and others in clockwise direction?
3
votes
1answer
135 views

Parallel axis theorem: adding mass

I'm going through a worked physics problem and have a question about the parallel axis theorem regarding only adding mass while not changing is axis of rotation. Here is the problem: A physics ...