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

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2
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1answer
63 views

Torque on a right angle triangle [closed]

I am attempting a question regarding the torque on a right angle triangle. The triangle is pivoted along the adjacent axis, there is no force acting on the opposite side, however there is a 12N force ...
1
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0answers
16 views

How to determine the right motor to rotate things? [closed]

Me and my teammates are trying to produce a motorized rotating bench. we want to rotate the bench to the other side if one of them get wet by the rain. we are currently doing the proposal for our ...
0
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1answer
55 views

Rotational motion: A cylinder, sphere and hoop rolling down a ramp [closed]

I have a question about comparing different objects in rotational motion. In this scenario: A cylinder (with moment of inertia = $\frac{1}{2}MR^2$), a sphere ($\frac{2}{5} MR^2$) and a hoop ($MR^2$) ...
0
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0answers
18 views

Relevant Archemidan Spiral Theorems: An Enquiry

Basically what I'm doing is investigating the solar wind's outflow. As part of this investigation is included a fairly crude application of a more complex outflow solution to that of basic archemidian ...
0
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0answers
49 views

Converting torque to angular velocity

Given the torque of a system, is it possible to convert this torque to the angular velocity of the object? I calculated the torque exerted by wind on a blade, however, now I need the RPM. To get the ...
0
votes
1answer
38 views

Clarification on what inertia and area moments?

This is something I have never understood despite applying the formulas in many classes. What I'm hoping to find here is some clarification. My understanding is that the first moment of inertia is ...
0
votes
1answer
37 views

Rolling cylinder on frictionless inclined plane

A cylinder is kept on frictionless inclined plane. Why it does not roll (it slides only), although torque with respect to contact point is working on it (due to component of weight parallel to incline)...
0
votes
1answer
49 views

Where does the formula for the moment of inertia come from?

I think I 'understand' the concept of moment of inertia, but I don't see why it is proportional to r^2 (for a given point). Is the equation just empirical?
1
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0answers
126 views

Why do trees sway?

Resonance can also occur in three dimensions (such as wind induced swaying) I tried to make a free body diagram (I know it is terribly wrong) to find the forces that causes the tree to undergo ...
1
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0answers
26 views

Angular velocity in body frame to displacement in lab frame?

For the case of a freely spinning symmetric top (no gravity), I derived the following equations, where $\omega_i$ is the angular velocity about a body-fixed axis: $$ \omega_1 = w_1 \cos (w_3 t) $$ $$ ...
3
votes
2answers
101 views

Why do tires with low air pressure experience more friction?

How does tyre pressure affect the frictional force on a tyre even though friction is independent of area of contact? And how does one analyze or calculate this friction?
1
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2answers
55 views

Does orbital motion cause rotation?

Assume the moon was flying freely in space, and not rotating at all. If if then happened to pass earth at just the right distance and velocity to fall into orbit, would its absolute rotation be ...
0
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0answers
79 views

Why did Einstein allow unphysical objects in his 1906 paper on $E=mc^2$?

In the first part of this paper, Einstein considers a "rigid cylinder", "massless cavity", as well as a "massless carrier mechanism" that is used to transport the massless cavity. These hypothetical ...
0
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1answer
35 views

Which force acts as centripetal force on gyroscope?

I think I have understood gyroscope in terms of angular momentum and how the torque of gravitational force moves it the way it does. Also I understand the direction in which it would move: What ...
0
votes
1answer
35 views

Is there no rotational mechanics for non rigid body? How do we deal with such situations in real life?

I am in 12th grade right now. We have a chapter on Rotational dynamics in which it is clearly stated that it is for rigid bodies. I understand that, Moment of Inertia will remain constant only for ...
0
votes
2answers
130 views

Normal Force in Circular Motion

In the above diagram, sec1(on the left side), an object of mass $m$, after releasing from rest from a slant track, continues into a vertical circular track. At a random position on the circular track, ...
0
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5answers
134 views

If I push or hit an object in space will it rotate or move along a straight line?

If I push or hit an object in space (vacuum and no gravitation) in direction what is not going trough its centroid, will it rotate or move along in straight line? I expect that on earth it will ...
0
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1answer
41 views

Please help me with this doubt from rotational dynamics

Torque to a magnetic field on a current carrying loop is same with respect to any point in space,is the same true for all force couples acting on any body?
0
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1answer
45 views

How to apply torque impulse

In the below question, can we apply conservation of Angular Momentum? If not, why? Moreover how do we apply Torque impulse to the system ? The contact force between the cylinders will be normal to ...
1
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0answers
34 views

Does a potential of interaction produce also torque?

I have a system of particles (spheres with masses and radii), with $6$ degree of freedom (they are free to move and rotate as they wish). Between each couple there is an interaction potential $V(d)$, ...
0
votes
1answer
45 views

Energy method to solving equations of motion? Why does this method work and what is it called?

Given the stated system in the photo we are suppose to prove simple harmonic motion when given an initial displacement $x$ I first considered the total energy of the system which we will call $H$ $$...
1
vote
2answers
66 views

Work done by a friction in rolling

When force is applied on extended objects at some point, the work done by this force on this object $\vec{F} \cdot \vec{dr_{P}}$ where $P$ is the point of application of force. When the object is ...
0
votes
1answer
96 views

Euler's laws - derivation

It looks simple and maybe is easy, but I don't get it. How to obtain the second equality from the first one below? Source: http://emweb.unl.edu/NEGAHBAN/EM373/note19/note19.htm They took ...
2
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1answer
35 views

What is the momentum change in a Foucault pendulum?

From the wiki page: If the plane of swing was north-south at the outset, it is east-west one sidereal day later. This implies that there has been exchange of momentum; the Earth and the pendulum ...
4
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2answers
2k views

How do I experience Earth's movement?

We are told that Earth is spinning on its axis at 1037 mph— something that we don't usually feel because of the environment that moves with us as well. Is there any experiment with which we can know ...
2
votes
1answer
207 views

To prove uniqueness of the rotation tensor associated with rotation of a rigid body

Suppose there are $N$ particles embedded in a rigid body which undergoes some random rotation such that: $$ \overline{\overline {R}}_{ij} \otimes \vec{a}_{ij} = \vec{b}_{ij}$$ where, $i$ and $j$...
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0answers
89 views

Simple powertrain dynamics

I'm trying to simulate vehicle powertrain and having problems at calculating correct impulse at the wheel. Here's what I have. Gear Ratio There are two gear ratio in the system $N_g$: ...
1
vote
1answer
75 views

What happens when one uses a blender in zero gravity?

I was recently told by a friend that using a blender type apparatus in a zero gravity environment will act like a centrifuge instead mixing properly. Is this the case? Furthermore, can anyone provide ...
1
vote
1answer
38 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 ...
1
vote
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 ...
3
votes
2answers
76 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 ...
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4answers
143 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 ...
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0answers
64 views

Trying to understand the physical intuition on finding/deriving effective rotation radii of a rigid body

This question is inspired from the answer of this If the rolling is assumed to be without slipping, we can solve the problem by conservation of energy: $$ mg \Delta h = \frac{1}{2}mv^2 + \frac{1}...
0
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1answer
72 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
57 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 ...
1
vote
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
vote
1answer
38 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 $...
1
vote
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
vote
2answers
58 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
votes
2answers
56 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, ...
0
votes
2answers
49 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 ...
1
vote
1answer
58 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 ...
4
votes
1answer
390 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 tyre(...
0
votes
1answer
46 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
59 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
65 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 ...
4
votes
1answer
37 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 ...
2
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0answers
105 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
221 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 ...
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 ...