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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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How does beam pinned at one end resist moment?

This beam is constrained by a pin at one end, so it is free to rotate around that point. If a moment M is applied, the beam cannot move since any rotation would involve motion of the COM, which is not ...
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4answers
120 views

Why do doors turn?

I really think that I might be overthinking it but I was thinking about a door. When you try and open it with a force, it will produce a translational AND a rotational effect on the door. Any good ...
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1answer
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Does LIGO accounts for Sagnac effect?

After reading Sagnac effect one thing immediately come to my mind is LIGO, I only read that the team building LIGO have already considered the curvation of Earth surface but what about Earth's ...
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0answers
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Find the possible values of friction coefficient [on hold]

Rod of mass M and length L is in rotational equilibrium and at rest. Thread connecting it to rough wall is incline at $\theta_1$ and $\theta_2$. Find all possible values of friction coefficient Say ...
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dynamics of a rigid body in a system of two linear drive [on hold]

I've been trying to solve the dynamics of this system for quite a while, but cannot seem to get the right answer. I've tried solving it with Lagrangian method but I am not so confident with the ...
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1answer
42 views
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45 views

Doubt regarding expression of angular momentum [on hold]

Two thin circular disc of mass $m$ and $4m$, having radii of $a$ and $2a$, respectively are rigidly fixed by a massless, rigid rod of length $l = \sqrt {24}$ a through their centers. This assembly is ...
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0answers
24 views

Gyroscopic Precession [on hold]

Two gyroscopes are made exactly alike except that the spinning disk in one is made of low-density barium, whereas the disk in the other is made of high-density gold. If they have the same spin angular ...
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1answer
37 views

How exactly does does friction rotate a wheel?

All I know is that the wheel pushes the ground and the ground pushes back (friction). Pls can anyone elaborate on this process?
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1answer
94 views

Physics mystery : why does it rotate?

In the beginning this thing was floating still and the candle was out. Then someone lit the candle and the flame somehow Made the object spin on the water. See the picture. I know a little bit about ...
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0answers
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Solve this question from rotational mechanics [on hold]

I would like to have a detailed solution.Please help.
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1answer
38 views

How can a body be rotating when it's translating?

How does a translating object (with constant velocity) seems to have a rotatory effect when viewed from a point not in its line of motion?
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2answers
38 views

Reason for neglecting frictional force in a particular type of Motion

A thin inelastic string is tightly wound on a cylinder. One of the ends of the string is attached to the above surface. Initially the whole system (string +cylinder) is held near the surface. When it ...
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2answers
56 views

Does torque provide rotation?

If a sphere is given a constant force along centre of mass, placed on a frictionless floor it does not undergo rotational motion as net torque about centre is zero. But why did we notice net torque ...
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1answer
39 views

Sliding to Rolling

In a problem where a sphere is initially sliding and then begins to roll after having travelled some distance. The thing that confused me is that the work done by friction on the sphere is not simply ...
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1answer
43 views

Steady solution for flow in Boussineq approximation in star [on hold]

I am trying desperately to find the solution indicated in this question : If I compute the equations on the 3 axis, I can't get the flow to be directed along $\vec{e_y}$ I have only : $$\dfrac{\...
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0answers
21 views

Lack of Gravity of an object suspended in mid-air [duplicate]

I Would like to know what would happen to an object suspended in mid air overtime as the earth rotates. with gravity not having effect on it as the earth rotate will it also move or will it stay in ...
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0answers
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Moment of inertia and rotational velocity? [closed]

The base of a record player is a disk that has a mass of 2 kg and a diameter of 34 cm. A child spins it so it rotates at a constant rate of 50 times a minute. Then, the child drops on a record (also ...
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4answers
70 views

Can you derive the acceleration of a cylinder rolling down an inclined plane by ONLY using conservation laws?

I want to solve the standard problem of a cylinder rolling down an inclined plane by only using conservation laws. In particular I want to use the equation: $$E_{pot}=\frac{1}{2}mv^2+\frac{1}{2}I\...
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0answers
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What are the fundamentals of motion in a non-inertial reference frame?

First of all, note that I understand what is considered off and on topic here. I'm posting this because I likely lack some sort of conceptual understanding of motion in non-inertial reference frames, ...
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0answers
36 views

Calculating the orbit's radius [closed]

The problem says: The angular velocity which describes a satellite in a circular orbit around the planet Venus is $\omega= 1.45 \times 10^{-4}$ rad/s and its angular momentum regarding the center ...
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0answers
25 views

Slipping of a rod -dynamics

A uniform rod of mass m is placed at right angles to a smooth plane of inclination $\alpha$ with one end in contact with it. The rod is then released. Find reaction of the plane when the ...
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0answers
31 views

Basic doubts about dynamics of a rod [closed]

I have few doubts in the given solution. It says there is no force along the plane but $mgcos\alpha$ is acting along the plane ? As given, $A$ is used as orgin. Then how come x-co-ordinate of $G$ is ...
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3answers
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Rotational movement of satellite in orbit

I would like to know how a satellite rotates around the Earth in terms of rotational movement. If it matters I'm interested in the helio-synchronous case -where the satellite is always visible from ...
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2answers
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Torque equation about center of mass frame

Let say a uniform cylinder is rolling down an incline. Since the center of mass of the cylinder has non-zero acceleration, should it be considered as a non-inertial reference frame? I know that when ...
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2answers
55 views

The acceleration of the point of contact, when a solid disc is rolling on a plank [closed]

A solid disc, initially at rest has a constant force applied on it, and it moves by rolling (pure roll) on a plank of the same mass (this plank can move as well - its on a frictionless surface). My ...
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5answers
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Why is torque defined as $r × F$ and not $F × r$?

Is it merely due to popular convention or does it supply any special clarification regarding other physical quantities?
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3answers
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For a solid sphere rolling (pure roll) up a slope (with friction) does friction play a role in slowing it down?

A solid sphere rolling up a slope is slowed down - is this only due to gravity, or is it also because of friction? I need to know this, to calculate the final translational and angular velocity of a ...
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2answers
81 views

Tire pressure physics

I understand that with less tire pressure you get more surface area on the pavement and more friction which gives more rolling resistance, but does having less air mean that there’s more weight per ...
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2answers
25 views

Rotational Dynamics equation from non inertial frames

Suppose instead of writing torque = Icalpha from the centre of mass, I want to write it from another non inertial frame. I know L = Lcm + RxPcm from any other frame , so if Idifferentiate it wrt time ...
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1answer
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Velocity And Angular Velocity Of A Sphere Rolling Down A Ramp

I was given a question on a recent test that asked me the following: A sphere is allowed to roll down a smooth inclined plane (No Friction), as it rolls down does its velocity remain constant, and ...
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1answer
41 views

Euler’s Equations of Motion for a Rigid Body and Inertial Forces

Euler’s equations of motion for a rigid body can be interpreted as a rewriting of Newton’s second law for rotations in a rotating frame. They basically tell us the sum of the torques equals the rate ...
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1answer
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What is the EMF in a bar rotating around any point?

The problem of a bar (or rod) of length $l$ rotating around one of its ends in a magnetic field of magnitude $B$ is very well known. The induced emf is $\frac{1}{2}B\omega l^2$, where $\omega$ is the ...
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2answers
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Rotating object on table: from sliding to rolling

A object which is rotating around a horizontal axis is placed on a surface, and starts sliding (with kinetic friction). After some time, it starts rolling without sliding through the table. The goal ...
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1answer
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Motorcycle wheelie: is it harder at higher speeds, and why?

I am trying to numerically prove that a motorcycle can do a wheelie from its engine power. However, when I use different methods, I get different results... please help connect the dots ! I see two ...
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0answers
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How to find centre of axis in spinning device using magnetometer data and accelerometer data

I've been trying to interpret data from a MEMS sensor inside a sphere that is spinning so we can find the axis of spin and rotation direction. As the device is moving and the devices initial ...
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1answer
40 views

Where to kick a ball to achieve rolling during the whole motion?

That's all the information I've got, so I don't really know what to do. But this is my idea: The equations of the motion are $$ma=F_0\delta(t)-F_{friction}$$ and $$\frac{2mR^2}{5} \frac{d \alpha}{d t}=...
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0answers
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Force required to drive an electric vehicle

I am looking for the equation to calculate the energy required to move an electric vehicle of simply design based on rolling resistance, weight, wheel radius and air friction. The idea is to build a ...
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0answers
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How would I find the angular accelertion of a disk rolling up a ramp? [closed]

I need to find the angular acceleration of a hollow ball rolling (without slipping) on a ramp, given the angle of the ramp theta, the mass and radius of the ball, and gravity and other physical ...
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0answers
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Who is credited with the discovery of rolling friction? [closed]

Which physicians discovered and/or contributed at large to what we know of rolling friction today, and what exactly did they contribute?
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1answer
66 views

What is the pressure under the lid of a rotating water bucket with lid?

Consider a water bucket with lid, the water is in contact with the lid and the lid is tight to the bucket The cross section of the bucket is circular, point A is the center of the circular section ...
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3answers
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Work done on Earth by car

Whenever a car accelerates, friction is pushing it forward. However, because the contact point doesn’t move relative to the earth, friction does no work. By conservation of angular momentum, the ...
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0answers
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Work done by static friction by a wheel

As I understand it, when a car is driving, work by friction is zero because if the wheel is not slipping, the point of contact is not displaced so work should be zero. But friction still causes a ...
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0answers
21 views

What analysis should I make when there is toppling question without specified axis? [closed]

For example - What maximum weight can be put on a table of 20 kg and radius 1 m with massless leg which are symmetrically placed on circumference so, it doesn't topple? Here, I don't know how to ...
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0answers
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Conceptual doubt in rotational kinematics

So in case 1, as I've drawn, due to opposing forces of equal magnitude, rod rotates about center of mass..agreed (rod is free here) in case 2 I've assumed that the second force is being provided as ...
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10answers
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How does an isolated body in deep space 'know' it's rotating? [duplicate]

We can imagine an object floating in the known universe, maximally distant from any other large mass. Maybe it has been there since coalescing after the big bang. What physical phenomena tell it ...
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1answer
38 views

Rotational motion

Today I was thinking a bit myself about circular motion and I come up with a doubt. Suppose we tie a string with a bob and then fix other end of the string with a support. Suppose the string is ...
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1answer
30 views

Force required for Angular Accleration

Suppose I have 4' x 4' piece of wood. Its mass is 150kg evenly distributed. I drill a hole right at a corner and place rod through the hole to create a rotational axis. I apply a tangental force at ...
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2answers
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Adhesion vs Static Friction

I feel like this question should have a simple answer, but I haven't been able to find one anywhere. I hope someone can help: In short, my question is why the force of static friction is so much ...
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1answer
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Predicting Rotation vs Sliding Forwards when Pushing an Object

Suppose there is a cuboid object sitting on a table, and a force is then applied to it. This figure shows the top-down view: I am curious to understand how the object will move due to this force, ...