A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.
Questions tagged [rotational-dynamics]
4158 questions
39
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4 answers
Could pressing the brakes on a car in mid-air affect its pitch rotation?
In a racing video game series named Trackmania, there is a game mechanic where when you hit a jump and the car is in mid-air, you can stop the car from pitching downward by tapping on the brakes.
I am curious if this mechanic has some basis in real…
13
votes
1 answer
Unfurling a toilet paper roll in the ISS
Consider a toilet paper roll floating ISS. Can an astronaut unfurl the roll only by pulling the loose end of paper (and not holding the rest of the roll in place, for example by using his finger as an axle)? I believe the answer is no, since we…
math_lover
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7
votes
3 answers
Do the rings in Mass Effect's mass relays (2-axis gimbal) describe a stable rotation?
Just out of curiosity. In the game Mass Effect, devices called mass relays contain two rotating rings, one inside of the other. See http://www.youtube.com/watch?v=qPxw5QjxhIs for an example, best seen around 00:10.
I was wondering: is this a stable…
JorenB
- 123
5
votes
2 answers
Toppling of a Rigid body
Consider a square block kept on a rough horizontal surface (friction is sufficient enough to prevent slipping/sliding). You apply a horizontal force F on the topmost point ,constant in magnitude and direction. The magnitude is adjusted so that the…
user150098
5
votes
3 answers
Why does the water bottle not rotate when it is half full?
Consider this water bottle:
When it is full and thrown up in the air, it rotates at a constant velocity.
When it is less than 1/8th full, the water bottle rotates even faster than when it was full.
When it is half full, however, the water bottle…
Jossie
- 557
4
votes
1 answer
Pure Rolling Motion
A small doubt in rolling motion. As we know, for pure rolling, the velocity of the lowermost point has to be zero wrt the ground or whatever platform it may be on.
Suppose, we have a body (let's say a ring) and it has velocity $v_0$. Assuming the…
Varun Sudhir
- 41
4
votes
3 answers
If an rod is hit at its edge with an impulse I, why would it move with the same velocity as if it were hit at its center?
In one of his lectures, Walter Lewin gives the example of a rod which is hit with an impulse on its edge. It starts rotating with angular velocity w, and its center of mass moves with velocity v. Assuming ideal conditions, he then continues to…
4
votes
3 answers
Are angular acceleration and velocity frame dependent?
Basically what I am trying to ask is if a body has an angular velocity $\omega$ or angular acceleration $\alpha$ about an axis then will it have the same angular velocity and acceleration along any other axis?
I am really confused .
As we know…
Tripti Khulbe
- 313
3
votes
2 answers
Perpetual Rotation of Rigid Body
Assuming no external torque or forces acting can a rigid body be set in perpetual rotation motion about an axis which is not its principal axis?
If no then does the earth continuously change its axis of rotation? as the principal axes of the earth…
programmer
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3
votes
3 answers
How to prove geometrically bottommost point of rolling wheel is in fact its instantaneous centre of rotation?
How can we prove geometrically that net resultant velocity of any point is perpendicular to line joining bottom of wheel to the point (and wheel is Rolling without slipping on a level surface)? Hence proving velocity vectors of all the points on…
Matt
- 644
3
votes
2 answers
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 what he means by a rigid change... is he saying…
Bozostein
- 253
3
votes
1 answer
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. I only know the radians per second (velocity) of…
Jose Garcia
- 31
3
votes
2 answers
can we calculate velocity of a spinning apparatus by just analysing the frequency of sound emitted by it
I have used a new term spinning apparatus as I was unable to name it.
I have tied a thread to a stone and was spinning it and I heard a sound something like that of a rotating propellor of a helicopter and then this idea stuck my mind
can i…
agha rehan abbas
- 750
2
votes
2 answers
The principal axis of a flat object
Let's assume that we have a flat object which has a random shape and does not have a symmetry axis. Let's assume the flat object lays in the xy-plane.
Any rigid body in principle has a set of three principal axes, which can be found generally by…
Stallmp
- 633
2
votes
1 answer
Where should I place a doorstop so it gets hit by the door with the least amount of force?
I was wondering if placing a doorstop the furthest away from the hinge means it will get hit with the most amount of force (position 3) when I swing the door open.
If that's true (and I want to prevent the doorstop from getting unglued from the…
nachocab
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