# Questions tagged [rigid-body-dynamics]

The study of the movements of a collection of connected bodies subject to external forces in the absence of deformation. This tag should be used for questions on the analysis of 2D/3D dynamics of rigid bodies, do NOT use this tag because your question contains a rigid structure.

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### Would a homogeneous rod on a fulcrum oscillate or remain at rest after displacement?

If I take a homogeneous rod, put it on a fulcrum, push one side down in a controlled way and release very carefully won't the rod just stay at rest in that new position? ChatGPT says that it would ...
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### Modeling centrifugal distortion with an effective charge distribution

The hamiltonian of a rigid object with a totally symmetric moment of inertia (i.e. a "spherical top") will depend only on the magnitude of its angular momentum. If we allow the object to ...
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### Do off-centre forces create additional energy?

When a force is applied to a rigid body at its centre of mass, it accelerates. Over time, that acceleration becomes velocity, which gives the body a certain amount of kinetic energy. However, if that ...
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### Angular Velocity of 3D object rotating in space

For a sphere rotating about z axis, its angular velocity is rate of change of angle of a radius vector in xy plane with x axis or y axis. I understand this clearly. But consider a 3d body which is not ...
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### What is the physical significance of Moment of Ineria about a point vs Moment of Inertia about an axis. In which types of problems we use the former?

I know the mathematical formula of both about an axis and a point. But where exactly we use moment of Inertia about a point. For 2d objects like discs rotating in its own plane, the moment of Inertia ...
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### Motion of bowling ball

I'd like to model the motion of an asymmetric bowling ball thrown on a bowling lane. I know there's forward momentum and angular momentum that moment the ball is released, and there's of course ...
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### Why isnt the contact force between the rack and wheel 200N?

I was looking at this YouTube video 'Example 1' (from 4:17 timepoint) and wondering why the contact force F between the rack and wheel isn't also 200N? Isn't this constant force of 200N being ...
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### Question on rotational dynamics

My book states that it's convienient to apply torque equation $\tau=I \alpha$ on instantaneous axis of rotation and centre of mass. My question is: why it is so? And how can we apply torque equation ...
1 vote
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### Is the idea of a rigid body compatible with Newtonian mechanics?

It is known that rigid bodies cannot exist in the framework of special relativity by causality arguments. But recently I saw a video on YouTube that claims rigid bodies are not compatible with ...
1 vote
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### Evolution of rigid body system using Impulse Based integration [closed]

I have been reading about physics engines, I have a reasonably OK understanding force based models and 6 dof integration. I'm still confused on how impulse based models work. What define the equations ...
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### Can torques cause both transitional and rotatory motion?

Imagine a rod (a rigid body) 10 meters long that is freely floating in space without being attached at any point. Its mass is 12 kilograms and according to most sources I found, its moment of inertia ...
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### What happens if we prevent gyroscope to precess?

If we apply some torque to spinning wheel in a vacuumed space in body frame y axis, wheel try to precess due to gyroscopic effect but it will be prevented by obstacles as seen from picture, what will ...
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### How to compute inertia tensor off the center of mass with geometric algebra?

I was reading Doran & Lasenby's Geometric Algebra for Physicists when I stumbled upon this, where $\mathbf{a}$ is a vector taken form the centre of mass. Returning to the definition of equation (...
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### Difference between the case where net force is zero and when no force is acting

I read online that the difference between the two cases is that the body deforms, but what if the body is perfectly rigid would there be another way to diffrentiate between the two cases? if not then ...
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### Does the direction of an angular velocity vector always stays constant with no force involved [duplicate]

Are there cases where there is a rigid body that rotates somehow and the direction of the angular velocity vector changes in the lab system?
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### Is energy conserved on a ball sliding without friction?

If a ball is sliding without friction (down an inclined surface) is energy conserved? I can’t think of why it wouldn’t be, but my intuition on this stuff is really bad.
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### Is this the correct way to integrate orientation given torque and inertia tensor?

I am trying to develop a 3D rigid body simulation in C++ in which I had some conceptual doubts on how to integrate for orientation given the total torque applied to a rigid body, and it's initial ...
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### Torque at only two points of contact between a rope and a disk (rigid body dynamic)

In physics, particularly when dealing with rigid bodies, there's a common practice of calculating torque at only two points of contact between a rope and a rotating disk, typically at the extremes ...
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### Energy conservation for a rolling rigid body

I came across this question where A solid cylindrical body of mass m and radius r rolls without slipping over a smooth inclined plane. Its initial velocity is v. What would be the maximum height ...
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### Centripetal acceleration of centre of mass towards instantaneous axis of rotation (IAOR)

When an object purely rolls on a horizontal surface, the centre-of-mass moves in purely circular motion, with respect to the instantaneous axis of rotation (IAOR). So does the centre of mass have an ...
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### Rigid body motion (RBM) transformation of interface points between a rigid and an elastic bodies

Above are pictures of a problem in mechanics. An elastic body occupying domain $\Omega$ is supported below with a fixed support and from above with a rigid body. The following calculations aim to ...
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### Direction of static friction in wheel [closed]

If a wheel is rolling right, that means the static friction on the stationary point that touch the ground is pointing left. That creates the torque that moves the wheel right. But if that stationary ...
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### How to tell if a force on a rigid body does any work?

In problems in Newtonian mechanics I often need to understand whether there is energy conservation. When only conservative forces (such as gravity) are present, it's obvious. But what about when we ...
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### Why can't rotations in general be associated with vectors?

In my textbook, there's a question: A vector has both magnitude and direction. Does it mean that anything that has magnitude and direction is necessarily a vector? The rotation of a body can be ...
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### Physical pendulum: axis of rotation

Why is the angular momentum always considered to be parallel to the angular velocity in physical pendulum problems, as if the axis of rotation were a principal axis always? I don't see the ...
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### Why when spinning over non-principal axis, it will change the axis of rotation?

Let's look at a disk which is rotating around non-principal axis. I know the explanation when looking in a rotating frame, the centrifugal force on the edges of a the disk create a torque that wants ...
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### How to determine the torque required to decelerate a rotating arm?

I am working in CAD on a robotic arm and wondering what is the appropriate way to determine Torque required from my actuator to decelerate the arm moving at some speed. Below I included a quick sketch ...
1 vote
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### Angular momentum about an axis other than axis of rotation [closed]

I know the formula for angular momentum about the axis of rotation i.e, $L = I\omega$. But what if I need to calculate the angular momentum about some axis other than the axis of rotation. Is it going ...
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### Rotational work by a force

If we have an object which is acted upon by a force which which produces both translational and rotational motion of body then would the total work done by the force be the sum of its translational ...
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### Doubt in rotational work-energy theorem

This is a question on work-energy theorem in rotational motion with its answer for the first part of the question. Here, I have a doubt about why is the book taking the translational work done by the ...
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### Combined KE for an object rotating about a point other than COM

I know the KE equation for combined translational and rotational motion, which is $K=Mv^2/2+I\omega^2/2$, and here $v$ is the velocity of COM and $I$ is the moment of inertia about the COM. But what ...
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### If a 100,000 ton container ship slams into a bridge at 8.6 knots how much energy was moved into the pylon and at what rate of transfer speed? [closed]

Edit: the entire question is in the title, the answer should be an amount of energy and a value of energy transfer in some unit, but not knowing enough about physics I don’t know what the appropriate ...
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### How does rolling without slipping happen physically?

In physics textbooks, problems about rolling usually include the assumption that the rolling is without slipping, meaning that $v=R\omega$ throughout the motion, where $v$ is the translational ...
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### Total kinetic energy confusion

This might be a stupid question or has already been asked before, so please refer me to the answer if it has. Let's say we have a rolling ball, which is purely rolling, and there is no friction. (Is ...
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My question is whether there is any known method, which doesn't use calculus, to find the speed of ball C, given that the speeds of balls A and B are given at a certain moment in time. Suppose that in ...
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### Question regarding dynamic modeling of cable driven robot

I am studying rigid body dynamics and am currently exploring the paper "Analytic determination of wrench closure workspace of spatial cable driven parallel mechanisms". In the paper, the ...
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### Two bodies rotation separation

I am currently working on programing a small simulation involving two bodies, yet I find myself somewhat unconvinced by the results I'm obtaining. Consider this particular test scenario: I have two ...
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