The rigid-body-dynamics tag has no wiki summary.
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Confusion in connected pulleys problem
I'm having some troubles in understanding why my reasoning doesn't work in the following problem:
Problem Two pulleys of mass $m_1$,$m_2$ and radius $r_1,r_2$ are connected by a belt (like chain ...
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1answer
54 views
Can a pushed plank beat light and break the laws of physics? [duplicate]
Imagine you are one lightyear away from a photon sensitive (light sensitive) switch. So it is obvious that light would take one year to reach to the switch. Now I have a one lightyear long plank. I ...
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2answers
70 views
Extension to continuous in proofs of rigid body mechanics
I'm studying rigid body mechanics and I've seen several proofs of properties related to total angular momentum, kinetic energy, etc. that all regard discrete set of points. For example, to show that ...
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1answer
40 views
A different proof for 6 degrees of freedom
I want a different proof of 6 degrees of freedom of a solid object made of $\ N$ particles. I am thinking along these lines:
Definition of rigid body is
$\ modulus[\vec{r_i}-\vec{r_j}]=constant \ ...
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2answers
61 views
Deriving $T = F\ r = I\alpha$ for a rigid body
For a single point mass :
$\tau=F_{t}r=ma_tr=(m r^2)\alpha = I\alpha$
For multiple point masses bound together : $\sum \tau_i = (m_ir_i^2)\alpha = I\alpha$
But how do we go from that to $I\alpha = ...
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1answer
50 views
Intuitive explanation for why same force applied farther from a hinge causes larger angular acceleration than if applied closer?
A standard example of a problem involving torque is opening a door - the same force F applied far from the hinge causes a larger angular acceleration than if applied close to the hinge.
I always had ...
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5answers
205 views
What do people actually mean by “rolling without slipping”?
I have never understood what's the meaning of the sentence "rolling without slipping". Let me explain.
I'll give an example. Yesterday my mechanics professor introduced some concepts of rotational ...
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0answers
120 views
Elastic collision of rotating bodies
How would you explain in detail elastic collision of two rotating bodies to someone with basic understanding of classical mechanics?
I'm writing simple physics engine, but now only simulating ...
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0answers
115 views
Deriving torque from Euler-Lagrange equation
How could you derive an equation for the torque on a rotating (but not translating) rigid body from the Euler-Lagrange equation? As far as I know from my first class in Classical Mechanics, there is ...
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2answers
258 views
What is the proof that a force applied on a rigid body will cause it to rotate around its center of mass?
Say I have a rigid body in space. I've read that if I during some short time interval apply a force on the body at some point which is not in line with the center of mass, it would start rotating ...
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2answers
283 views
Which is the axis of rotation?
This should be simple, but it keeps bothering me. If a rigid body has no fixed axis, and a torque (defined relative to a point $A$) is applied, it will rotate around $A$. But often I can also ...
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2answers
144 views
Kinetic energy of a cylinder
It is a long cylinder (you can approx $R=0$), and it has a fixed point in one os its ending points, it's rotating on a plane and I have to calculate the kinetic energy from reference systems situated ...
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1answer
132 views
Force and Torque Question on an isolated system
If there's a rigid rod in space, and you give some external force perpendicular to the rod at one of the ends for a short time, what happens?
Specifically:
What dependence does the moment of inertia ...
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1answer
183 views
Can any physical rigid body be represented by an ellipsoid with the same angular dynamics?
According to wikipedia, the inertia tensor of an ellipsoid with semi-axes $a,b,c$ and mass $m$ is
$\left[\begin{array}{ccc}
\frac{m}{5}(b^2+c^2)&0&0\\
0&\frac{m}{5}(a^2+c^2)&0\\
...
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2answers
140 views
Rigid body dynamics of tossing of a coin
While tossing a coin, it is commonly experienced that you get a head, if you toss it up with the head side up, and a tails if you toss with the tails side up. Is there a mathematical proof of this ...
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3answers
90 views
Reference for the predictability of rigid body dynamics
I'm looking for a reference, journal article, paper, etc. that supports the idea that classical mechanics, in particular rigid body dynamics, is largely predictable.
A view coming from the background ...
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1answer
184 views
How to determine the probabilities for a cuboid die?
Imagine we take a cuboid with sides $a, b$ and $c$ and throw it like a usual die. Is there a way to determine the probabilities of the different outcomes $P_{ab}, P_{bc}$ and $P_{ac}$? With $ab$, ...
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1answer
67 views
Rigid body/moment of inertia problem
I have a homework assignment about rigid body dynamics. Take a disc of radius $r=2m$ with uniform mass density $\rho=1$ $kg/m^2$ in the x-y plane, resting in an inertial frame. At some instant, a ...
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2answers
253 views
Precession of angular velocity about the body-fixed axis
My textbook mentions that under force-free motion of a symmetric top, its angular velocity vector $\overrightarrow \omega$ precesses about the $z$-axis of the body-fixed coordinate system. This seems ...
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2answers
466 views
degree of freedom of a rigid body 5 or 6?
I'm confused here. I have a three particle (rigid) system. What would be the degree of freedom? I found out five. 3 coordinates for center of mass and 2 for describing orientation.
But we have only ...
3
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1answer
491 views
Conservation of linear and angular momentum
Suppose I have two rigid bodies A and B and they are connected by a spring which is attached off-center (thus possibly causing torques). Due to the spring a force $f$ acts on A and a force $-f$ acts ...
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3answers
317 views
Understanding Tensors
I don't seem to be able to visualize tensors. I am reading The Morgan Kauffman Game Physics Engine Development and he uses tensors to represent aerodynamics but he doesn't explain them so I am not ...
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2answers
128 views
Unexpected potential energy increase during Tic-Tac drop
I dropped a Tic-Tac:
(no worries, it happened before), and I noticed as it bounced on the floor that it would first jump 20 cm high, and at the next bounce for instance 50 cm high. Shouldn't it ...
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3answers
90 views
Rotationally invariant body and principal axis
Suppose a rigid body is invariant under a rotation around an axis $\mathsf{A}$ by a given angle $0 \leq \alpha_0 < 2\pi$ (and also every multiple of $\alpha_0$).
Is it true that in this case the ...
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1answer
142 views
Will a precessing spinning whell fall down if there is no friction at all?
If there where no friction at all, would a spinning wheel held up by one end of the axis spin precess forever without falling down?
I just asked another question about the same problem:
Direction ...
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3answers
856 views
Direction of torque precession of a spinning wheel
Consider a spinning wheel, which is held up by one end of it's axis like this:
To explain why the change of angular momentum is directed as shown in the figure above, one usually says that there is ...
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6answers
612 views
Degree of freedom paradox for a rigid body
Suppose we consider a rigid body, which has $N$ particles. Then the number of degrees of freedom is $3N - (\mbox{# of constraints})$.
As the distance between any two points in a rigid body is fixed, ...
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1answer
416 views
How to calculate the coefficient of restitution for 2 bodies?
I have 2 rigid bodies (from different materials) in a collision.
As you know I should have the coefficient of restitution value to get the velocities after collision.
What is the information/values ...
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3answers
229 views
how to represent the effect of linking rigid-bodies together?
I have 2 rigid-bodies (b1,b2) if i linked one to the other (as if they are conjoined together) , how to represent b1 effect on b2 and b2 effect on b1
Is there any LAW that affect the ...
4
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1answer
357 views
How do you combine two rigid bodies into one?
With respect to some fixed frame of reference, given the inertial tensors, positions, orientations, and angular and linear velocities of two rigid bodies, how do you combine them to make a single ...
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2answers
518 views
How fast does force propagate through matter? [duplicate]
Possible Duplicate:
Is it possible for information to be transmitted faster than light?
Consider the following thought experiment. You have a long perfectly rigid beam (for the sake of ...
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1answer
302 views
Applying a force on a rigid body on a certain point
I have a rigid body with an origin point (at the center of mass).
I want to apply a force on a certain point.
So what is the force applied to the origin of this rigid body?
Description image:
...
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What kind of shape has the lowest flutter wind speed?
What kind of shape has the lowest flutter wind speed and is the most unstable?
I mean for rigid body.
Thanks
Yes, I know many factors affect the flutter in a MSD system (for rigid body), however ...
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1answer
1k views
Tennis serving machine— How does a spinning ball bounce?
I have an idea of making a tennis serving machine. I will briefly describe what it is:
The machine is configured to serve the ball at a fixed speed to the center of the left (or right) service court
...
2
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1answer
454 views
Physics needed to build a top down billiards game [duplicate]
Possible Duplicate:
How are these balls reflected after they hit each other?
I was wondering what sort of physics equations would I need in order to build a top down billiards game? I tried ...
