# Tagged Questions

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.

24 views

### Principal moment of inertia for a rotating body

My major is not in physics. I am reading the following paper: (my problem is simple and not related with any optimization) http://arxiv.org/abs/1410.2841 (p.5~p.6) Suppose The ...
39 views

### Simple Disk rolling with slipping on a horizontal plane

This is the first time I've encountered this scenario. I want to understand how to handle it. Since the disk is slipping, what would be the work done by the frictional force? What is the ...
46 views

### Work done by internal forces of a rigid body

I am reading Goldstein's Classical Mechanics book, and I came across that: In a rigid body the internal forces do no work Is this statement based on the assumption that the internal forces are ...
24 views

### Stuck with 2D kinetics problem [on hold]

I've been trying to solve this exercise for the last four hours and I'm totally stuck. The problems goes like this: Given the mechanism in the image, located in the vertical plane, the OB cord ...
36 views

### Kinematics of Rigid Body [on hold]

I'm working out in this problem since last week but I'm not able to identify how to calculate the total angular momentum. Can anyone help me? A uniform disk of mass $m$ and radius $r$, mounted on a ...
32 views

### Rolling Coin (Old Physics Quals Exam) derivation help [duplicate]

I am trying to understand the derivation for the angular velocity of a rolling coin in the problem given on this website: http://functionspace.com/question/27/answer/121 How does one find angular ...
75 views

### Is it possible to throw a stick without giving it a rotational motion?

When walking with our dog I always throw wooden sticks for her. Then one time I wondered if I could throw the stick (normaly, so not like a spear) without imparting on it a rotational motion around ...
55 views

### Two Rolling logs

Suppose we have two logs rolling down a hill, one of gold and the other of wood; the acceleration for both will be equal, something which is unclear to me; I get that this may be due to their form, ...
35 views

### Rotation of a rod due to a normal force

Suppose there's a rod suspended in space free from the effect of any force. Let a force F act at a distance x from one end. How can i prove that rotation will take place about an axis passing through ...
89 views

31 views

### Is there a form of rigid body dynamics that uses unit quaternions instead of Euler angles?

I’d like to know specifically about an elegant way of deriving a second derivative of an orientation quaternion from a torque and a moment of inertia matrix, if one is available. The straight forward,...
183 views

### Why does a rigid body rotate and not simply translate when pushed with an instantaneous force?

Let's say we have a metal rod of consistent density sitting flat on a frictionless surface. I intuitively understand that if I push one of its ends away from me, (at a right angle to the length of the ...
37 views

### Conceptual understanding behind moments of force for a rigid body cylinder

I have a question behind the conceptual understanding of the following equation: $$\frac{\text{d}}{\text{d}t}\mathbf{L}_G = \sum_i \ \mathbf{r}_i\times \mathbf{f}_i$$ where $\mathbf{L}_G$ is the total ...
46 views

### What's behind the moment of inertia and other “body-global” properties of bodies?

I'm an electrical engineer currently doing some (computational) mechanics stuff. In introductory literature about mechanics, you can read plenty about the moment of inertia and how you use it in ...
54 views

### Differential equation of motion of combined rigid body

I am reading the following paper: http://tinyurl.com/jv2pu2m I have a question about (1) and (2): To (1), I think the following link provides good explanation. Equation of Motion for Rigid ...
37 views

### instantaneous velocity center

The instant center of rotation, also called the instantaneous velocity center is the point fixed to a body undergoing planar movement that has zero velocity at a particular instant of time. For ...
34 views

### Finding the Mass of a Precessing Top

Consider a symmetric, non-nutating precessing top with one point fixed (the tip if you will). It's symmetry axis is at an angle $\theta$ to the vertical and it steadily precesses at some angular ...
22 views

### rigid body dynamics - equations of motion if CM coordinate system not coincident nor aligned with body axes

My goal is to find inertial expressions for velocity and displacement components for a satellite subjected to an external torque (from a thruster aligned to the body system). I've reviewed some texts ...
44 views

### Spinning top fixed point

I have seen many explanations about the movement of a spinning top. The explanations were in a varied level, from basic newtonian mechanics to Lagrangian formalism. But I do not understand why some ...
76 views

### Where is the mistake in the following rationament [duplicate]

Well... kind of hard to translate in English so bare with me :). Let's consider a wheel that spins in the void. Each point of the wheel has the speed $v = ω r$. That means that for any $ω$, there is ...
54 views

### Finding $\theta$ at any point in time [duplicate]

I am looking to simulate the movement of a steel beam which has a constant mass $m$, and that has a pivot $O$ at one end that is moving with a constant horizontal velocity with magnitude $v$. ...
75 views

89 views

### Rolling without slipping in absence of friction force

I'm confused about a rolling without slipping situation. Suppose to have a disk of radius $R$ on a floor, and exert a horizontal force at a certain distance $r$ from the center of mass. I would like ...
20 views

### Ring Ascending a Step

Consider a thin circular ring of mass $m$, radius $r$ rolling without slipping with velocity $v$ towards a step of height $h$ $(<r)$. Assume no rebound and no slipping at the time of contact. What ...
48 views

### Why is the center of mass frame always used in rigid body dynamics?

In most of the cases the center of mass is chosen for rigid body motion description, but this is not an obliged choice, since the motion of any point $P$ of the rigid body can be seen as the ...
48 views

37 views

### Two bodies connected to each other with with a string of lenth L is a rigid body? [duplicate]

Suppose we have two bodies A and B, they are connected to each other with an ideal string of length $L$. Then is this system a rigid body? This system has 5 degrees of freedom ( 6-1 constraint). But a ...
34 views

For the description of rigid body motion, any point $O$ of the rigid body could be taken as reference, since the velocity of a generic point $P$ can be written in function of the angular velocity $\... 2answers 31 views ### Velocity of the points of a rigid body The most general motion of a rigid body is a roto-traslation. Firstly is it correct that any point (let's call it$O$) of the rigid body can be seen as the point through which passes a istantaneous ... 2answers 70 views ### Meaning of parallel axis theorem: why is the moment of inertia minimum if the axis passes through the CM? From parallel axis theorem follows that, given a rigid body, the moment of inertia is minimum if calculated with respect to an axis passing through the center of mass. What is the physical meaning of ... 1answer 36 views ### Component of angular momentum perpendicular to the rotation axis in rigid body rotation I have difficulties in understanding, in the rotation of a rigid body, the properties of the component of the angular momentum vector$ \vec {L} $which is perpendicular to the fixed axis of rotation$...
I'm studying rigid body motion on Landau but I'm having troubles to understand this proof of the fact that the angular velocity $\vec{\Omega}$ is constant for a rigid body. My doubt is about the ...