A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.
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1answer
323 views
Calculation for force generated by a rotating rectangular blade
When trying to calculate the lift force generated by a simple rectangular blade, I've found the following equation: $$F = \omega^2 L^2 l\rho\sin^2\phi$$ in which $\omega$ is the angular velocity, $L$ ...
1
vote
2answers
408 views
Moment of inertia of a coin
I have a a coin infinitely thin, rotating along the diameter.
How to derive the formula for it's moment of inertia passing through the diameter.
I was suggested to use the surface density and ...
1
vote
3answers
2k views
Factors affecting torque and RPM of a motor
I'm not a physics guy, not even basic concept of a DC motor is easy for me. My question is, how these parts of a motor affects it's RPM and Torque? I had my research a while ago so I filled out some, ...
2
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0answers
539 views
Forces and torques about the CENTER OF MASS of a physical pendulum
I'm currently stumped by the following situation. Say we've got a rectangular physical pendulum (think ruler with a hole-punch at one end).
It's trivial to analyze the motion of the pendulum with the ...
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1answer
95 views
How to find replacement function of a mass?
I wonder how I can find the replacement function of the center of the blue mass? The center of mass of the blue mass is $(0,0)$ and the blue mass is homogeneous. The masses do not move at t=0 in the ...
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1answer
519 views
Moment of inertia of a sector about its center point?
What is the moment of inertia of a pizza slice that has a radius r, an angle (radians) of theta, and a height of h about the center point perpendicular to the cheese plane?
4
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1answer
187 views
Does the Moon's orbital inclination follow the wobble in the Earth's rotation?
As the Earth wobbles during rotation, does the higher gravity at the equator tend to pull the moon toward an equatorial orbit even as the earth does that thousands of years wobble cycle? It would ...
2
votes
3answers
138 views
Effect of surface treatment on fair dice
If I have a perfectly balanced and thus fair cubic die, then polish 3 adjacent faces (so that their coefficient of friction is effectively zero) and roughen the remaining faces (so that their ...
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4answers
615 views
17 Joules of Energy From a Mouse Trap
Do you think it would be possible to get 17 joules out of a standard size mouse trap. By my math, it is a torsion coefficient of 3.45 or so out of the spring.
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2answers
437 views
Altering Venus rotational speed to match Earth's via weather manipulation
Venus rotates approximately 6.5 km an hour Earth rotates approximately 1650 km/h how fast could we speed up Venus's rotation via only weather manipulation ( maybe a giant fractal lens between Venus ...
1
vote
0answers
238 views
How equivalent are heat energy and work energy in connection with a spinning flywheel?
Let's say we have two identical spinning flywheels, that have arbitrary geometry, and are made of copper.
Now we apply some heat energy at the center point of flywheel A, causing it to slow down a ...
4
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5answers
452 views
What happens to angular momentum when matter is converted to energy?
Let's say a spinning star radiates mass-energy only from it's pole regions. How does the loss of mass-energy effect the angular momentum of the star?
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1answer
178 views
Angular velocity $\omega$ by $v$
We have two girls, with mass (M). They become close to each other in speed of V. The distance between them is 3L.
I was asked to calclute the Angular velocity (w) of the two girls. So I set the ...
2
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1answer
85 views
Synchronising the Earth's rotation via mass redistribution
How much material would have to be moved per year from mountain-tops to valleys in order to keep the Earth's rotation synchronised with UTC, thus removing the need for leap seconds to be periodically ...
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2answers
179 views
Problem based on Rotational Motion #2
One fourth length of a Uniform Rod of mass $m$ and length $x$ is placed on rough horizontal surface and it is held stationary by means of a light thread as shown in the figure. The thread is brunt ...
2
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0answers
147 views
Why do control moment gyroscopes exhibit “torque amplification”?
There are a number of articles that describe the benefits of using control moment gyroscopes (CMGs) over reaction wheels in inertial navigation applications. One of the primary benefits of using a CMG ...
2
votes
3answers
223 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 ...
1
vote
1answer
225 views
Problem based on Rotational Motion [closed]
A spool of mass $\mathsf m$ and inner radius $\mathsf r$ and outer radius $\mathsf{2r}$, having moment of inertia $\Large\mathsf{\frac{mr^2}{2}}$ is made to roll without sliding on a rough ...
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vote
1answer
1k views
Would a light or a heavy ball roll fastest down a slope?
A small, light ball and a larger, heavier ball are released from the top of a slope.
Which will move further? which will come down faster?
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vote
2answers
687 views
Will a boiled egg or a raw egg stop rolling first?
If we roll a normal egg and a boiled egg at the same time on a floor
1) with friction
2) without friction
which one will come to stop first (if they will stop at all) and why?
Can anyone tell ...
0
votes
0answers
327 views
How to design a hand rotate dynamo [closed]
I want to make a dynamo which can produce electricity. My requirements for the dynamo are as follows.
I need to charge my laptop through this.
I want my laptop to run for 1hour with this energy ...
2
votes
1answer
106 views
Is it humanly possible to change Earth's axis?
Just what the title states with the qualification that the change must be affected without using other celestial bodies as mentioned in the Clarke/Baxter SF 'Sunstorm'.
Obviously given the momentum ...
1
vote
2answers
214 views
Why do balls in a spinning ellipsoid move to the minor axis plane?
There is a question concerning the Physics of a small child's tall that has been bothering me for some time now. I have investigated this to a small degree, but I have not been able to find a ...
2
votes
1answer
186 views
What happens to a rotating rod that breaks in two?
I know that the approximation for the moment of inertia of an infinitely thin rod of mass $m$ and length $L$ spinning around an axis perpendicular to its own axis at its center is $\frac{mL^2}{3}$:
...
2
votes
0answers
193 views
Levitation rotation speed involving laser acceleration, pyrolytic graphite and a vacuum
The experment would involve a small NIB magnet levitating between or on the diamagnetic material pyrolytic graphite, unlike other forms of levitation this doesn't require power to run such as ...
2
votes
1answer
180 views
What “I” should use in Rotational Energy formula $(I \omega^2)/2$
$\text{Rotational Energy} = \frac{1}{2} I \omega^2$. What $I$ should be used?
$I$ as a inertia tensor matrix = stepRotation * inverse moment of inertia * inverse stepRotation;
Or I as moment of ...
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0answers
184 views
How to model an accelerometer measurements on a car wheel?
I am working on kinematically modelling an accelerometer on a car wheel.
When working on the initial conditions, I am confused whether or not I should use the gravitational acceleration since there ...
19
votes
1answer
987 views
Why does this object periodically turn itself?
See this video about 30 sec in. http://www.youtube.com/watch?v=dL6Pt1O_gSE
Is this a real effect? Why does it seem to turn periodically?
Can it be explained by classical mechanics alone?
Is there a ...
2
votes
3answers
492 views
Why do some satellites fall to Earth?
In another question How does Newtonian mechanics explain why orbiting objects do not fall to the object they are orbiting?, one can read an affirmative answer. They how do you explain satellites ...
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0answers
79 views
How long will the bar to travel 1.50 cm threaded rod? [closed]
A threaded rod with 12.0 turns / cm and 1.18 cm in diameter is mounted horizontally. I screwed a threaded rod with a hole to attach to the bar. The bar rotates at 237 revolutions / min. How long will ...
5
votes
1answer
855 views
Why are infinitesimal rotations commutative, whereas finite rotations are not?
Infinitesimal rotations commute and every finite rotation is the composition of infinitesimal rotations which should logically mean they also commute; but they don't. Why?
3
votes
2answers
139 views
understanding why inversion cannot be accomplished by a rigid change
Goldstein pg 151 says "it is clear that an inversion of a right-handed system into a left-handed one cannot be accomplished by any rigid change in the coordinate axis..." I am trying to understand ...
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0answers
299 views
Should angular momentum change or it should not.?
Let us consider a body with an arbitrary shape. Let its center of mass be assigned coordinates (o,o,z) with respect to an origin.Now let us consider two equal and opposite forces acting on the body ...
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3answers
21k views
Linear acceleration vs angular acceleration equation
I'm learning about angular velocity, momentum, etc. and how all the equations are parallel to linear equations such as velocity or momentum. However, I'm having trouble comparing angular acceleration ...
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1answer
159 views
What causes a gyroscope to eventually rotate/fall over?
Hey so I've just learned about angular velocity and momentum and how torque changes it.
Looking at a wheel spinning around an axis, with one end being held up by a rope, what causes the wheel to ...
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0answers
527 views
Rolling on an inclined plane [closed]
Let us consider a sphere. let it be released from rest from the topmost point of an inclined plane. Now let it come to a rolling motion, after a time x seconds. We can say that at time t= x seconds ...
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votes
2answers
189 views
Which Axis of rotation?
Let us consider a body , A, of arbitrary geometrical shape of mass m1. Now let it be translating with a speed v. Let us consider a small point particle ,P, of mass m2. Suppose it strikes A with a ...
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votes
1answer
391 views
Lean angle of a turning bicycle
I'm asked to derive a relationship for the leaning angle of a bicycle with the following specs:
Center of gravity for bike and rider is a distance $L$ above the ground when vertical, and the total ...
6
votes
1answer
305 views
Spin-up time for fluid in an open cylinder with no endwalls?
I'm interested in how quickly (if at all) the fluid in an open cylinder would reach solid-body rotation if the cylinder is suspended vertically in an unbounded fluid.
I've found plenty of work that ...
5
votes
2answers
290 views
Does rotational energy have effect on gravity/metric?
Intuitively, if energy can be stored in rotational motion, it has to obey $E=mc^2$.
Does rotation of typical stellar-sized objects - BHs, pulsars, binaries - have measurable effect on their overall ...
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5answers
589 views
Why does the weighing balance restore when tilted and released
I'm talking about a Weighing Balance shown in the figure:
Press & Hold on onside of the horizontal beam and then release it. It makes some oscillations and comes back to equilibrium like shown ...
5
votes
3answers
399 views
confused about ball rolling and rotational energy
I was solving a practice test problem and it was just a conservation of energy problem
where a spherical ball is falls from a height h to the ground such that
$$mgh = \frac{1}{2}mv^2 + ...
2
votes
1answer
222 views
How to know the time a disc takes to stop from rotating and the numbers of revolutions
Assuming I rotate a disk, I want to know how long it takes to completely stop, and the number of revolutions it made since I removed my fingers off the disk.
Lets say a DVD I rotate with my fingers. ...
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vote
0answers
160 views
Any interesting physics theroies/equations to be used in a video game? [closed]
I am designing a little game based on Newtons Graviational Law.
Are there any theories that I can use to create games?
thanks
3
votes
4answers
300 views
N particles, will there be any rotation after a period of time or everything will collapse
This is in context of classical Newtonian physics.
Consider a system of n different point mass particles. Initially all are spread around on one plane. No particle possess any velocity to begin with. ...
1
vote
1answer
133 views
Is it theoretically possible for the orientation angle of a projectile to remain exactly equal to the orientation of velocity?
This question is sparked by my answer to this question: Is this simulation following real physics?
After examining the math, I don't see how it is theoretically possible for the situation simulated ...
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vote
1answer
217 views
Is this simulation following real physics?
I am trying to simulate a game in Box2D(Physics engine). The game that I am trying to simulate is very simple and can be found here: http://www.makaimedia.com/#/speartoss
What I want to know is that, ...
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1answer
209 views
Artificial Gravity - Spinning Station Questions II
In an answer to Artificial Gravity - Spinning Station Questions Vintage wrote:
A theoretical space station of radius 900 meters, doing a complete rotation every 60 seconds (in order to generate ...
3
votes
4answers
790 views
Outcomes of earth slowing down spinning on its own axis
What are the possible outcomes if earth slows down spinning on its own
axis?
To be specific:
Can the decrease in the internal centrifugal (or centripetal) force due to slowing down earth's spin:
...
2
votes
3answers
412 views
The rotating movement of an asteroid
I almost all movies where you could see an animation about an asteroid, they move in a very distinct way.
I don't know how to explain better, but I think what we can see in the movies is that the ...
