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Questions tagged [rotational-dynamics]

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

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Centripetal Force Formula Confusion

After I finished studying and trying to test my knowledge to see what I have learned, I realized I am confused about the centripetal force formula: $$F_c= \frac{mv²}{R}$$ which I know is also equal to ...
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28 views

Angular velocity of rigidly rotating orbit in 3D

Consider a circle in 3-dimensional space. On this circular orbit, a rigid bead moves, thus changing its angle $\phi$ with a reference radius on the circle. The intrinsic angular velocity is given by ...
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0answers
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Difference between torque, moment and couple

I know the basics of them like Torque is force multiplied by the distance (from the point where there is no rotation like centre of gravity). Couple acts because of two equal and opposite forces ...
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1answer
67 views

How To Determine The Position Vector [on hold]

The question I have been set is as follows. A car of mass $m$ is driven at constant speed $v$ around a circular test track of radius $a$, which is banked at an angle $α$ to the horizontal. With ...
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1answer
40 views

Centripetal force related problem [on hold]

If a bike rider constantly keeps rotating on a vertical circular path, what is the required minimum velocity on the highest point of the circle to keep him on the circular path without falling?
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32 views

Rotating disk with a chain [on hold]

I need help with this problem, dont know where to start. A chain with mass $m$ stretched around a disk of radius $r$. Tension in chain is $T$. Find coefficient of friction $\mu$ if when disk is ...
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1answer
33 views

Euler's equation of the rigid body's dynamics - Vector form with rigid body's angular acceleration

I have the following Euler's equations (9.23) ($\omega $ is the rigid body's angular velocity, $\Omega$ is the angular velocity of the reference frame whose origin is fixed on the rigid body and whose ...
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0answers
47 views

Torque From Spinning Cylinder [on hold]

I was asked the following question The way I tried to solve it is I Tried to figure out the change in momentum (per second) when the liquid goes around the bend and equate it to the impulse to find ...
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40 views

The moment of inertia of a hollow sphere, except that there is a hole [on hold]

The moment of inertia of a hollow sphere is $\frac{2}{3}mr^2$, where $m$ is the mass and $r$ is the radius. If a hollow sphere is rotating anticlockwise with reference to the axis of rotation at its ...
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1answer
25 views

Angular acceleration of a double compound pendulum [on hold]

How can I calculate the angular acceleration of a double compound pendulum? I'd like to know what the angular acceleration of each of the pendulum's center of mass will face at any point in time. PS -...
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1answer
30 views

Force around corner [on hold]

I am having big trouble with this exercise: Exercise 6: A weight with mass 6 kg slides without friction along a circle-shaped pipe. In the end is a spring with constant k=60kN/m. The weight is ...
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1answer
39 views

Can an elliptical planet be stable?

Subsequent to This question about the Earth's actual cross-sectional shape at the equator, I'm wondering about the stability of non-spherical planet-sized masses. Suppose there is a planet of uniform ...
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Angular Velocity About Instantaneous Axis of Rotation [duplicate]

If you consider a cone of half angle φ rolling without slipping on a plane with angular velocity Ω as shown in the figure. What would be the angular velocity about the Instantaneous Axis of rotation? ...
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1answer
35 views

How do you sum up torques for a macroscopic object

Torque is measured about a point. But angular momentum for some object is measured around an axis. This doesn't make sense to me as in for example, a cylinder. If there are multiple tangent forces on ...
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1answer
36 views

Angular acceleration about 2 different axis

is angular accelaration or angular velocity about an axis passing through COM same as that of angular acceleration about any other axis passing through the same body?
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1answer
22 views

Moment of inertia of solid sphere [closed]

Why isn't the moment of inertia of a solid sphere (9/64)piMR², but (2/5)MR²?
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4answers
126 views

Rotational analogue of Newton's 2nd law

If we are writing torque equation about general point what points must be taken into account for getting the correct result. Also If that general point is accelerated then how do we deal with this. ...
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0answers
12 views

Why does the ball on a string produce results consistent with angular energy conservation? [closed]

This third party experiment confirms exactly that angular energy (rotational kinetic energy) is conserved and not angular momentum. The gentleman announces his only genuine result at 5:40. Thereafter ...
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0answers
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Have I solved the question correctly?if not, please help [closed]

Is everything correctly done? kindly help me if it isnt
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0answers
37 views

IE Irodov (question 1.138) [closed]

A horizontal plane supports a stationary vertical cylinder of radius $R$ and a disc is attached to the cylinder by a horizontal thread of length $l$. An initial velocity $v$ is imparted to the disc. ...
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1answer
28 views

Rotating sphere and the velocity of particle at the surface

If a sphere is rotating with speed $\omega$ and has a radius $r$, then after one complete revolution what would be the velocity of a particle at the surface (neither at topmost or point of contact of ...
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1answer
80 views

Three Dimensional Torque on a Sphere

Assume that we have a sphere in 3D space. Let point $A$ rest on the surface of the sphere. I can apply a force $F$ of any magnitude and any direction, so long as it points tangential to the surface ...
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4answers
59 views

How does a tangential force cause a linear acceleration?

Consider a rigid sphere in empty space of mass m and radius r. If a tangential force(torque) F (or any force not along the line of the centre of mass) is applied, it is my knowledge the sphere will ...
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2answers
44 views

Horizontal component of Coriolis force in an aircraft: compensating force with its wings angle

I have the following problem: "An aircraft is flying at 800 km/h in latitude 55◦ N. Find the angle through which it must tilt its wings to compensate for the horizontal component of the Coriolis ...
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0answers
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Work done by friction on a oscillating disc without slipping in a circular path

Say a disc is oscillating without slipping in a circle about its stable equilibrium. I've thought of it this way: I assumed a disc is placed at, say, 3 degrees from the equilibrium. The rotation ...
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2answers
77 views

Angular Momentum in a Straight Line

Edit: This is not a duplicate question. The other question asked how angular momentum remained constant if the distance varied. This question asks why you can select any point and calculate angular ...
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1answer
32 views

Angular Dispacement, velocity, acceleration [closed]

What is the effect of angular velocity and acceleration on circular motion as they both have direction so what is its effect?
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1answer
62 views

Weight Distribution of a Heap of Logs

Suppose that you have a heap of logs. Each log is the same length $l$, the same mass $r$ , and the same radius $r$. For simplification, their rotational inertia is $I=\frac{1}{2}mr^2$, their ...
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1answer
57 views

Collision of rotating sticks

Q: Two identical uniform sticks are rotating about their stationary centers with equal angular speeds. The vertical stick is slowly raised until its top end collides with the center of the horizontal ...
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4answers
62 views

Kinetic energy, angular momentum of a rotating body

We have a disk rotating about an arbitrary axis, and we can supposedly quantify the kinetic energy of such a disk by $K = \frac 12Iw^2$. Now, it is also true that, as the disk is rotating, each ...
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3answers
61 views

Torque due to friction on a series of disks

Recently I was looking at two situations involving friction and torque. The first situation seemed pretty straightforward at first. A disk of mass $m$ and radius $r$, with a coefficient of static ...
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0answers
38 views

Why rotation creates bulges? [duplicate]

I remember when in class i saw a video where a rotating ring was bulged at the equator. What is the reason of this phenomenon? Is the same reason that earth is not a perfect sphere?
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3answers
81 views

Requirement for being in rotational equilibrium

An object in rotational equilibrium has no net external torque: sum of all external torques = 0 Does it mean "rotational equilibrium" may mean that the object is not rotating ... or it may mean ...
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1answer
53 views

Rotational work done

So the formula for rotation work is $$\mathrm dW=T\cdot\mathrm d\theta$$ where T is torque. While solving a question like in case of a body rolling down an incline (pure rolling), we usully equate ...
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0answers
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What is the Time Period of Rotational Spring Mass Harmonic Motion [duplicate]

If I want to know the time period of a rotational spring mass in harmonic motion, how to figure it out? for example, a spring with a mass inside a tube(no friction in tube for example) , and the tube ...
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1answer
48 views

Why does an increase in height decrease the spin time of a spinning top?

We know that an increase in height of a spinning top decreases the time it spins for without toppling. Why does this happen? I suspect that this is connected to the fact that an increase in height of ...
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0answers
11 views

Why spinning creates bulges? [duplicate]

Earth isnt a perfect but has bulges because of its spinning. What actually creates the bulges? Is the same reason that makes a liquid have v shape in a rotational tube?
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3answers
37 views

When does a wheel stop slipping?

I am learning about friction in rolling motion in my high school physics classes and I don't have much intuition about this. If a wheel is rolling and slipping there is a dynamic friction involved, so ...
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1answer
36 views

How do I calculate the tensor of inertia of a non-rigid body?

How do I calculate the tensor of inertia of a rotating non-rigid body? Is the usual formula: $$T_{ij} = \int{\rho( x_ix_j - \delta_{ij} x^kx_k)d^3x}$$ still correct?
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2answers
35 views

Calculating torque about a point [duplicate]

While calculating angular acceleration in a problem, about which point should we calculate the torque and why?
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1answer
56 views

A question on rotation [closed]

Question: A spool of mass $M$ and radius $2r$ lies on an inclined plane. a light thread is wound around the connecting tube of the spool (radius of connecting tube is $r$) and its free end carries ...
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0answers
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Why is it that a stationary bike will fall but a moving one won't? [duplicate]

No matter how much I think about this I can't come up with a reason to me there is no difference In the forces acting against the tilting of the bike in both the cases as mothion is in the ...
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2answers
110 views

Rotating Rod in Special Relativity

Statement of the Problem In frame $F'$ with co-ordinates $(t',x',y',z')$, a straight rod rotates in the $x',y'$ plane with angular velocity $\omega ′$ about one of its ends. The fixed end is located ...
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2answers
74 views

Does the friction between the tires of a bicycle and the ground increase as speed increases?

My question is quite simple "Does the friction between the tires of a bicycle and the ground increase as speed increases?" I know that drag does increase as velocity increases, but what happens to the ...
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1answer
121 views

The physics of a cornering wheel and its centripetal force

Can a rolling wheel create a side force without first rotating on a vertical axis? There is something wrong with the way we describe how a cornering vehicle wheel creates a cornering force. I think ...
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0answers
15 views

Torque, Rotational motion [duplicate]

Slow precession can be used to determine a much more rapid rotational frequency. Consider a top made by inserting a small pin radially into a ball (a uniform sphere) of radius R = 6.0 cm. The pin ...
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1answer
24 views

Rotational kinetic energy of a body [duplicate]

How to find total kinetic energy of a body which is rotating about multiple axes at the same time? For example consider a wheel with a shaft, and that the shaft is hinged. So the wheel is rotating ...
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1answer
35 views

Kinetic energy of disk rotating around axis parallel to the one through its center [duplicate]

Given the situation shown in the figure below. A thin disk with mass m and radius r is rigidly connected to one end of a massless rod with length l at its centre, with the other end of the rod ...
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2answers
42 views

I am confused about which point we should take moment of inertia (moi) in diff situations

A uniform rod of mass m and length l is kept vertical with lower end clamped. It is slightly pushed to fall down under gravity. Find angular speed of rod when passing through its lowest position. I ...
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3answers
76 views

Difference between center of mass and center of gravity

Let's consider a very tall building (g would be variable) which is rotating with the earth naturally. Now do the centrifugal force and the gravitational force act on the same spot? If not why does the ...