Questions tagged [rotational-dynamics]
A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.
4,487 questions
1 vote
0 answers
36 views
Rotating-wave approximation (RWA) for two-tone spectroscopy
I am having a hard time figuring out what the correct rotating-wave approximation (RWA) should be in a two-tone spectroscopy simulation. Apologies in advance for this being an easy question, I work ...
- 11
4 votes
1 answer
162 views
Two spools linked via a pulley: only one rotates. How to conserve energy?
I know how to get the correct answer for the following problem using dynamics, but when I approach it using the energy formulation I get the wrong answer. Two massive, identical spools are attached to ...
- 43
-1 votes
3 answers
148 views
What force(s) is rotation made of? [duplicate]
Can the rotation of an object be viewed as the result of two perpendicular forces ('push' and 'pull') that have combined? When I spin a wheel there is a 'push force' at a right angle to the wheel's ...
- 121
4 votes
2 answers
280 views
Angular momentum conservation for a rolling ball after an initial impulse
First a ball gets an impulse $J$. Why can we say that $$Jh = I_cm w,$$ when it is clear that the friction force is also acting around the CM of the ball. When balacing forces around the CM we see that ...
- 41
2 votes
0 answers
69 views
How to obtain the third gravitational potential term from this series?
In this paper the gravitational potential between a point mass and an extended rigid body is $$ U = -\mathbb{G}m_1\int_B \frac{\mathrm{d}^3 \mathbf{Q}'\rho(\mathbf{Q}')}{|\mathbf{r} + \mathrm{C}\...
- 187
2 votes
1 answer
111 views
What are the Euler-Lagrange equations of an approximated rigid body and a point planet interacting via gravity?
The potential due to a rigid body will be approximated using a Lagrange polynomial expansion as $$ U(x,y,z)=-\frac{\mathbb{G}Mm_p}{r} - \frac{\mathbb{G}m_p(I_1 + I_2 + I_3)}{2r^3} + \frac{3\mathbb{G}...
- 187
1 vote
2 answers
45 views
Can a Massless Pulley with no friction be treated as a massless circular object with no friction?
A pulley usually involves a rotating axle to change the direction of tension. However I read in my Textbook that for an ideal pulley, this need not be the case, and you do not need to consider any ...
- 15
0 votes
0 answers
35 views
Could cometary non-gravitational acceleration be linked to surface cohesion transitions?
In several comets, including the interstellar comet 3I/ATLAS, a non-gravitational acceleration is observed, i.e., a net thrust not fully accounted for by gravity. While outgassing is known to produce ...
- 101
2 votes
2 answers
83 views
How is using the principal axis frame in the Lagrangian allowed?
The kinetic energy of a fixed, rotating rigid body is $$ T =\frac{1}{2}\mathbf{\omega}\mathbf{I}\mathbf{\omega}=\frac{1}{2}I_{xx}\omega_x^2 +\frac{1}{2}I_{yy}\omega_y^2 + \frac{1}{2}I_{zz}\omega_z^2 + ...
- 187
7 votes
5 answers
2k views
Will a Coin rotate always about its diameter/com when Tossed?
When a coin is tossed in the air by applying an impulse at some distance from the Centre of Mass (centre of ring), it will start rotating and move up vertically as well. Can we say that the coin will ...
- 73
-1 votes
1 answer
72 views
Rotational motion Problem [closed]
Problem statement: A block of mass m and a cylinder of mass $2m$ are released on a rough inclined plane. The plane is inclined at an angle $θ=45$ degrees with the horizontal. The coefficient of ...
13 votes
5 answers
500 views
Football rolling down a hill
I rolled an American football down a gentle slope of about 10°. Regardless of how I started it, after some distance, it tended to roll around the short axis ($y$-axis). I expected it to roll around ...
- 507
0 votes
1 answer
52 views
Rotation of wind in low and high pressure zones
Why do winds rotate counterclockwise around low-pressure systems and clockwise around high-pressure systems in the Northern Hemisphere? If this rotation of wind is because of the Coriolis effect ...
- 507
0 votes
1 answer
56 views
Principal axis of circular disc with removed circular portion [closed]
From a circular disc, a circular portion of radius R/2 has been removed....it is asked if the axis YY' is principal axis or not...so my first intuition was since the axis is not symmetric this should ...
- 1
-1 votes
1 answer
109 views
Bucket rotated in a vertical plane [duplicate]
This was a "give the reason" question in my textbook. If a bucket containing water is revolved fast in a vertical plane, the water does not fall even when the bucket is completely inverted. ...
