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

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0answers
21 views

Torque due to non-uniform force [on hold]

Suppose a non-uniform force, varying along with the distance, is acting normally on the surface of a rod hinged at the mid point. The force varies along the length of the rod, i.e as we go down along ...
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0answers
27 views

How to calculate angular momentum in this scenario?

The answer to part a) is 1080. However, for part b) I don't understand why the equation wouldn't simply be $I_i\omega_i = I_f\omega_f$. Why do we have to subtract $m_bv cos \phi$ from ...
2
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1answer
50 views

To which side will it move? [on hold]

Children pull the carousel with diverse forces (as in the picture below). In which direction will the carousel move? Calculate the torque. I have done the following: The torque of the force that ...
4
votes
1answer
40 views

Optimal size for a bike tire

While I was riding my bike funnily enough I wondered if there was an optimal size for a bike wheel. So I suppose that is my question, What is the optimal size for a bike wheel? If the bike accelarates ...
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1answer
22 views

Period of oscillations of a pendulum made of two disks (K&K 6.15) [Solved] [on hold]

This is my first question on Physics Stackexchange, so, please suggest any edits I should do to my post. The question is: A pendulum is made of two disks each of mass M and radius R separated by ...
0
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1answer
45 views

Are there any exceptions for law of conservation of angular momentum?

I just wrote a medical entrance test, in which this question appeared a person sitting firmly over a rotating stool has his arms stretched, if he folds his arms, angular momentum about the axis of ...
0
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0answers
25 views

Mechanics - Rotational Inertia [migrated]

I am facing a problem solving a mechanical system which is shown in the scheme below. We assume that coupling of the two shafts is done with a clutch Equations: ...
0
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0answers
22 views

Acceleration of an oscillating object in a frame of reference that is itself rotating!

I have been reading a paper and due to my limited knowledge of Physics, I can't move ahead. Sorry I do not know latex so, I will snip the paper and paste it here. So here goes it..... I think ...
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1answer
27 views

Moment of Inertia Calculation [closed]

A uniform disc has centre O, radius a and mass 2m. It is free to rotate in a vertical plane about a horizontal axis through O. A particle P of mass m is placed on the highest point of the rough edge ...
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0answers
13 views

How do you calculate the angular momentum of a dumbbell after a collision? [closed]

In outer space, far from other objects, a small block of mass $m$ traveling at speed $v_1$ approaches an object initially at rest that consists of two small spheres each of mass $M$ connected by a ...
0
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0answers
32 views

Calculating the 3-dimensional torque on a non-uniform rigidbody given the angular acceleration about its center of mass

Say I have a rigidbody, made up of several point particles with known masses and positions relative to the center of mass. How would I find the torque on this rigidbody given its angular acceleration ...
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1answer
78 views

When will the pringles can fall?

When I'm pushing a tall, cylindrical object stood on its end (like a Pringles can) I can push it near its bottom, and it will slide forwards, or push it near the top, and it will topple over. So, ...
0
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1answer
28 views

Does mass distribution/center of mass affect free fall?

An everyday is example would be cars. If you were to drop a car, not taking air resistance into account, would a front-heavy car tumble forward as it fell? And a car with a perfect 50/50 front/rear ...
8
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4answers
849 views

Paradox in applying Newton's second law [duplicate]

Suppose I apply two vertical but opposite forces with the same magnitude in a body like is shown in the picture: According to newton's second law, the center of mass shouldn't accelerate, since the ...
1
vote
1answer
34 views

How do you define the total rotational energy of an object?

This problem arose when I was applying a conservation of energy argument to a mechanics problem, (a spinning coin on a table) and wasn't sure how to define the total rotational energy of the coin. At ...
0
votes
1answer
10 views

what is intertia tensor for tapered cylinder (solid and with separate inside and outside radii)

I need the inertia tensor for tapered cylinders, both solid and hollow, and if possible with independent inner and outer radii on the x and y axes (so the cross-sections of the cylinders can be an ...
0
votes
1answer
24 views

What is the long-term effect of a continuous off-set force, acting in a frictionless environment?

An example would be if a satellite had a rocket on one edge, which were to fire continuously. I can see that there will be both lateral and rotational acceleration, but what I am less clear on is ...
2
votes
2answers
91 views

How many hours will be in a day if the radius of Earth increases by 70 m?

I am little confused about the linear momentum and angular momentum, will the linear momentum of earth change due to changing of its radius or it will stay as it was and i know that the moment of ...
2
votes
2answers
50 views

Why does the period/frequency of a fan slow down significantly when I taped a piece of rubber band to it?

All of this was done with a standing fan set horizontally on a table. During an experiment, I had to tape a piece of rubber band to one of the standing fan's blade and measured the period of the fan. ...
0
votes
3answers
57 views

why does a ball roll

I searched for my question and I found many results but all of them eventually try to solve something specific (like solving for the kinetic energy or finding when does the ball stop). what I want ...
1
vote
1answer
44 views

One force applied to one point of a rigid body: centre of mass and torque [duplicate]

Let us suppose that one force is applied to a point of a rigid body that is not acted upon by any other force. I think an example can approximatively be a rock in deep space, far from any relevant ...
2
votes
2answers
76 views

Will the day/night cycle change when the poles melt?

I want to know what will happen to day and night if poles melt i think it will change but I don't know why? ^_^
27
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9answers
3k views

Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...
0
votes
1answer
46 views

Why doesn't the string slack in the motion in a vertical circle even if tension is zero?

Suppose a particle of mass $m$ is attached to an inextensible string of length $R$ and is undergoing vertical - circular motion. The centripetal force is given by the tension & its weight: $$T ...
3
votes
1answer
41 views

Angular momentum-torque relationship in a rotating frame?

I have read that $$\vec\tau=\frac{\mathrm{d}\vec L}{\mathrm{d}t}$$ holds true whenever the origin is not accelerating. But I cannot see why this holds true for a rotating frame of reference (such as ...
0
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1answer
41 views

Can an object experience torque when the only applied external force is at its axis of rotation (IOW, where $F \times r = 0$)?

This question came up because of this diagram that I saw in my textbook of an angular simple harmonic oscillator. I've always struggled a bit with torque and rotational dynamics in general, and I ...
2
votes
2answers
84 views

Clarify excerpt from Feynman Lectures on rotations in three dimensions

In The Feynman Lectures, vol. I, chapter 20 Feynman discusses rotations in three dimensions and explains angular velocities may be added as vectors; in particular he says: What about angular ...
3
votes
1answer
265 views

Why are three parameters required to express rotation in 3 dimension?

We know that in spherical coordinates angle $\theta$ and $\phi$ (two angles)are enough to express three dimensional rotation of matrix. But to express rotation mathematically as a transformation ...
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0answers
41 views

Degeneracy of Rotational Energy Levels of a Diatomic Molecule

To derive the energy levels of a diatomic molecule (with the z axis the axis of symmetry of the molecule), we write the Hamiltonian as ...
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0answers
37 views

Rotational Spectrum of a Diatomic Molecule

The rotational energy levels of a diatomic molecule are given by $$E_l=\frac{\hbar^2}{2I}l(l+1)$$ where $l$ is an integer. If the molecule is a dipole it can emit or absorb electromagnetic radiation ...
1
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1answer
36 views

Rolling in V shaped groove [closed]

In this set up I've been asked to work out the linear acceleration down the slope. It's said to be instantaneously rolling around the axis AB $Ma=Mg\sin(\theta)-2F$ where $F$ is the frictional ...
1
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1answer
23 views

Consideration of centrifugal force during descent

If we imagine an object falling from a height h above the surface of the earth. We can go into a rotating frame and therefore introduce Coriolis and centrifugal forces. Using the Coriolis force the ...
13
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4answers
477 views

How can I relate linear and angular motion using a single formula?

I want to relate linear and angular motion using a single formula. Assume I have a 10m rod, and I apply a force of 5N on it, 2.5m away from the axis of rotation for 1s. How can I determine the ...
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0answers
32 views

Name for the transformation into an accelerated frame?

A transformation into a frame that looks at an experiment from a rotated perspective is called a rotation. A transformation into a frame that moves with a different constant velocity is called a ...
2
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0answers
54 views

What is the physics in a balero toy?

A balero is a wooden ball tied with a string to a rod. The string ties to the ball at one end (say North pole), and there is a hole drilled in the ball at the other end (South pole). The hole is the ...
0
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1answer
35 views

Angular velocity formula for a particle?

I know that when the motion of a particle is circular about the origin then: $$\vec v=\vec \omega \times \vec r$$ But that this does not hold for any motion with a radial as well as tangential ...
0
votes
3answers
98 views

Torque on a disc?

In the following diagram: Point(c) is a going into the page and attached to the disc, Point(c) applies a torque($\tau$) to the disc, and it starts to rotate due to that torque. And if point(c) was ...
0
votes
1answer
31 views

Cancelling internal forces/moments term when deriving inertial matrix

I am attempting to derive the inertial matrix for a general rigid body of mass $m$ as shown in the following diagram: The green vectors indicate the key position vectors: Position of centroid ...
0
votes
1answer
48 views

Since Earth spins, would an aircraft travelling opposite to direction of Earth spin take less time? [duplicate]

Suppose we want to reach the point on earth which in relative terms is exactly on the opposite end of the sphere we call earth (I know it is not an exact sphere). We either dig vertically downwards, ...
1
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0answers
23 views

Gears in contact?

I was doing a practice exam paper question that was along the following lines: A gear, $A$,and moment of inertia $I_A$ is spinning about its axis at angular velocity $\omega$. Another gear $B$ ...
1
vote
2answers
69 views

What should we do If we wanted to increase the angular velocity of a planet? [duplicate]

We could hit it with really fast objects, but could we manipulate the orbit of a large satellite to speed up its rotation? What would be the easiest way?
2
votes
1answer
51 views

Ball rolling on half-pipe

It is well-known that a ball rolling down a half-pipe where the side it starts on has enough friction for the ball to roll without slipping and on the side other to be frictionless, that the ball will ...
0
votes
1answer
81 views

Finding time period of oscillations in a multiple spring system attached to a solid cylinder [closed]

A solid cylinder of mass $m$ and radius $R$ is kept in equilibrium on horizontal rough surface. Three unstretched springs of spring constant $k$, $2k$, $3k$ are attached to cylinder as shown in the ...
0
votes
2answers
31 views

When I change the rpm of a turntable, how long does the turntable to get to the new rpm?

If the turntable was rotating at 16 rpm and I switched it to 30 rpm, is the change in speed pretty much instantaneous, or is their a period of acceleration? When I did it, the change appeared to be ...
1
vote
1answer
45 views

Angular velocity and instantaneous rotation axis

Let's suppose that we have a cylinder of moment of inertia $I$ rolling on the floor without sliding, moving with linear velocity $v$ and rotating around an axis passing through the center of mass with ...
-1
votes
1answer
55 views

A Textbook Problem From Rigid Body Dynamics(Cengage Bm Sharma) [closed]

I was going through my textbook examples on rigid body motion. In this problem i can understand the derivation of equations 1,2 and 3,but can someone explain me the 4th equation?Please!!1
0
votes
1answer
40 views

Rotational Equilibrium Problem [closed]

The question is as follows: One end of a uniform 4.0-m rod, whose weight is w, is supported by a cable that makes an angle of 37° with the horizontal. The other end of the bar rests against a wall ...
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0answers
22 views

Calculate angular velocities and alpha values?

A lightweight bar, stiff stick of length L, at either end are two small spheres of mass $m_{1} = m_{2} = m$. Bar may turn in vertical horizontal axis passing through point O on the way its a bar ...
0
votes
3answers
70 views

Maximum acceleration for a vehicle [closed]

I'm in engineering school and we have a project: we have to build a amphibioues vehicle; I'm looking for a formula. Our vehicle has to go as far as possible with its unique source of energy, a ...
-1
votes
3answers
101 views

Finding the angular velocity of a rod hit at a distance from its pivot [closed]

A 1m long, 2kg stick is nailed to the wall with a single nail, allowing it to pivot and freely rotate at the end. A 1kg ball, with speed 3m/s makes contact with the stick at some distance x (unknown) ...