Skip to main content

Questions tagged [rotational-kinematics]

A tag for questions about rotational motion, including angular velocity and angular acceleration.

Filter by
Sorted by
Tagged with
0 votes
3 answers
47 views

If we take a sufficiently large axle for a wheel then is it possible that the top of the wheel would have thrice the velocity of its axle?

I recently learnt that the top of a wheel has velocity twice that of its axle. In all such cases of why this is so the axle is always considered to be very small in comparison to the wheel. Thus, I ...
Madly_Maths's user avatar
1 vote
0 answers
33 views

Rotating Tank of Charged Liquid

Consider a long rectangular tank of dimensions a×b, where a≫b, that is rotating at a constant angular velocity and filled with an incompressible charged fluid. How would one find an equation ...
moe gus's user avatar
  • 11
0 votes
0 answers
36 views

Linear approximation of the magnetic dipole field

Summary: using 3 angles to represent a magnetic dipole's orientation is redundant because the rotation around the $z$-axis of the dipole does not change the magnetic field, there are only 2 DOFs for ...
William Lin's user avatar
0 votes
1 answer
62 views

Does spinning the umbrella slow down the fall more?

Ignoring its structural weakness, if you jump from some height and use an umbrella to slow down the fall, would making it spin while you're falling affect the speed in any way?
Flamethrower's user avatar
0 votes
1 answer
43 views

Relative motion between two points on a rotating disc

Consider two children A and B sitting on diametrically opposite points of a merry go round rotating about its centre. Suppose A and B are facing each other. As seen from A, B never seems to move and ...
Johnsmith's user avatar
  • 133
0 votes
0 answers
56 views

How can we show that $((\vec v · \vec r) \vec r )'$ corresponds to Coriolis force?

We have: Position as $\vec r$ Velocity as $\vec v=(\vec r)'$ Acceleration as $\vec a=(\vec v)'$ Angular velocity as $\vec \omega = \frac{\vec r × \vec v}{r^2}$ Angular acceleration as $\vec \alpha = ...
Navneet's user avatar
  • 261
1 vote
0 answers
72 views

Angular velocity versor

I am going back through the definitions of good old Euclidean vectors and trajectories to see whether when i was younger i missed important concepts. In my notes, and reference book, i found that for ...
LolloBoldo's user avatar
  • 1,611
4 votes
2 answers
115 views

Kinetic energy of an ellipsoid

I am trying to solve the following exercise, taken from Landau's Mechanics: Find the kinetic energy of a homogeneous triaxial ellipsoid, rotating around one of its axes (AB, fig. 44), while the ...
user1255055's user avatar
0 votes
1 answer
42 views

Index notation for the generalized form of the velocity gradient with shear and rotation

Good day guys, I was studying fluid dynamics and came across the following equations (shown in the image): When we have both shear and and rotation, they each contribute to the change in velocity ...
STOI's user avatar
  • 286
1 vote
0 answers
43 views

The stupidest question ever on relative kinematics and angular velocity [duplicate]

I am scratching my head on a very basic formula whose meaning escapes my intuition. On basically all texts of mechanics the following result is derived: Suppose that a rigid body is moving with ...
ebenezer's user avatar
  • 130
1 vote
3 answers
49 views

How is momentum conserved in this collision with loosely-connected spheres?

There are three identical spheres. B and C are loosely connected with a light inextensible string, and A approaches B directly at some initial velocity $v$. There is no angular momentum. A and B have ...
spraff's user avatar
  • 5,148
0 votes
4 answers
85 views

What is the moment of inertia $I$ when angular velocity $ω$ is zero?

$$I = \dfrac{L}{\omega}$$ What is the moment of inertia when $\omega = 0$? Is it just not defined or is the formula not valid when $\omega = 0$?
Krishn Sharma's user avatar
0 votes
1 answer
191 views

Circular motion at relativistic speed

I am working on a personal hard science-fiction project but when I analysed the following situation, in the context of special relativity my conclusion seems counter intuitive and perhaps I am ...
hello world's user avatar
0 votes
0 answers
47 views

When a wheel begins to roll on a flat surface, is it due to fulcrum generated at the contact point by friction?

[Edit: What I'm trying to understand is how any wheel rolls on a surface, instead of just spinning in place. I know that friction provides the force to make the wheel roll, but I'm unsure about the ...
cosmos's user avatar
  • 1
19 votes
3 answers
5k views

Does the top of a wheel really move at twice the velocity of the center?

According to the physics of a wheel rolling without slipping, the topmost point moves twice as fast as the wheel. But I tried an experiment: Take a wheel on a table and hold a ruler horizontally in ...
Manukrishnan P's user avatar
2 votes
2 answers
75 views

If a weak light source is attached to a string, and someone swing this light source in circle. It seems that this light source is brighter. Yes or no

It may be truly a question of life and death. You know those glow sticks. As a sailor it is a good idea to carry one on our lifevest. Falling into the sea, those glow stick make a light source that ...
Pierre magnard's user avatar
1 vote
2 answers
59 views

Euler Rotation Equations and invariance of vectors in different reference frames

Consider two frames, one which is inertial and the other one rotating w.r.t. to the inertial frame. Say there is a rigid body having angular momentum which is same/invariant in both frames. How is it ...
JAY YADAV's user avatar
1 vote
1 answer
75 views

How does relative motion work for an extended object?

I have this conceptual doubt which might be flawed very badly but I don't understand this particular thing. For example, if one end of a stick is moving with velocity $v_1$ and the other with $v_2$, ...
Krave37's user avatar
  • 123
0 votes
1 answer
38 views

Position vector in the formula relating the velocity in rotating frame to inertial frame [duplicate]

When learning the position vector $\:\mathbf r$, I was told it was not a real vector because it is tied to a particular coordinate system. Now I have learned that the derivative of any vector $\:\...
Chuan Huang's user avatar
0 votes
2 answers
85 views

Linear velocity on a circle

Consider a ball rotating around the z-axis with constant angular velocity $\vec{\omega}$, then the linear velocity $\vec{v}$ is given by $\vec{v} = \vec{\omega} \times \vec{r}$. It is easy to ...
Chuan Huang's user avatar
0 votes
0 answers
21 views

Closed form solution for the linear acceleration of a particle on 3D rotating object given momentum and MoI?

Is there a closed-form solution for the linear acceleration of a particle on a rigid body undergoing some arbitrary rotation in 3D with no external forces, given its angular momentum vector and its ...
Gabi's user avatar
  • 357
3 votes
2 answers
74 views

Vector Associated with Rotation Matrix

I am reading the $3^{\mathrm{rd}}$ edition of Goldstein's Classical Mechanics, and on p. 165 in Chapter 4 around eqs. (4.67)-(4.68), the authors derive the transformation matrix corresponding to a ...
Georgy Zhukov's user avatar
0 votes
2 answers
90 views

Does relative motion allow for speeds $>c$?

If motion is relative, (so if X was stationary and Y was moving at v m/s, we could think of this as Y being stationary and X moving at -v m/s), could we not create a scenario in which a stationary ...
bbqribs2000's user avatar
0 votes
1 answer
36 views

Wrong concept in rolling question

A solid sphere of radius R is placed on smooth horizontal surface. A horizontal force F is applied at height h from the lowest point. For the maximum acceleration of centre of mass, which is correct? ...
Starlight's user avatar
  • 347
0 votes
1 answer
81 views

Why need the extra definitions for rotational motion?

Why do we need to define things like angular momentum, torque, etc.? I want to do everything with fundamental quantities. The conservation of angular momentum relies on the conservation of linear ...
Bilal's user avatar
  • 3
3 votes
2 answers
539 views

Energy loss due to friction in Rolling Motion

I understand why rolling motion does no work. My (possibly imprecise) summary of the answer is that net work done is zero. And the role of friction is to convert translational kinetic energy into ...
Starlight's user avatar
  • 347
0 votes
0 answers
50 views

Created a resource to help solve a problem I was having in a lab. Can I publish it?

I had to complete a lab for school assessing the accuracy and precision of calculating a triangular prism’s moment of inertia using a trifilar pendulum. When I wanted to compare my lab results to ...
3 votes
1 answer
187 views

Speed at which the Moon moves past a point on Earth's surface?

I'm trying to calculate how fast a point on the surface of the Moon is moving past a point on the surface of the Earth (I assume a point on the equator of each for simplicity). I know the Earth is ...
tansvaal's user avatar
0 votes
2 answers
53 views

Angular velocity relative to some frame

In "Introduction to Robotics" by John Craig, we have the following statement: The vector ${}^A \Omega_B$ describes the angular velocity of $B$ with respect to $A$, and ${}^C({}^A \Omega_B)$ ...
user3180's user avatar
  • 202
1 vote
0 answers
6 views

Should the rotary vane damper torque be less than the load torque?

The rated torque of a rotary vane damper should be less than or more than the load torque? In my opinion, if the rated torque is greater than the load torque of the damper, then I believe my ...
BigBrain69's user avatar
0 votes
3 answers
119 views

Understanding the meaning of the directions of $\vec\omega$ and $\vec{L}$

I'm struggling with some basic intuition regarding the angular velocity $\vec\omega$ and angular momentum $\vec{L}$ vectors, for any arbitrary motion. Specifically, I'm trying to figure out what the ...
Aviv Cohn's user avatar
  • 605
0 votes
1 answer
45 views

Combined KE for an object rotating about a point other than COM

I know the KE equation for combined translational and rotational motion, which is $K=Mv^2/2+I\omega^2/2$, and here $v$ is the velocity of COM and $I$ is the moment of inertia about the COM. But what ...
yyzr's user avatar
  • 97
2 votes
1 answer
79 views

Understanding angular velocity $\omega$ as a vector

I would like to validate my understanding of angular velocity as a vector. Suppose we have a particle $P$ moving around in $3D$ space in some arbitrary way. At any given point in time, we would like ...
Aviv Cohn's user avatar
  • 605
3 votes
1 answer
107 views

Rotation of a sphere on two different axes

You have a small globe, which is mounted so that it can spin on the polar axis and can be spun about a horizontal axis (so that the south pole can be on top). Give the globe a quick spin about the ...
Kanav Choudhary's user avatar
3 votes
2 answers
181 views

Can the same rough surface provide frictional force on opposite directions for translation and rotation of a sphere under a tangential external force?

I came across a question which says: "A force $F$ acts tangentially at the highest point of a sphere of mass m kept on a rough horizontal plane. If the rolls without slipping , find the ...
Synthia's user avatar
  • 57
0 votes
2 answers
88 views

Angular Velocity and Angular acceleration when the position vector is changing

I was watching a lecture about circular motion and how angular velocity and angular acceleration differ if origin changes.The teacher at 9:10 says that we cannot apply the formula $a=rα$ as position ...
PinkAura's user avatar
  • 349
0 votes
1 answer
53 views

Relative angular acceleration

Let us consider a particle which is rotating in a circle of radius $R$ with a uniform angular velocity of $ω$. We are observing this particle from a frame rotating about the same axis with uniform ...
Physics_enthus's user avatar
0 votes
2 answers
58 views

Is the angular acceleration and the resultant acceleration the same thing? [closed]

Is the angular acceleration and the resultant acceleration of tangential and centripetal acceleration the same thing in non-uniform rotational motion? If not, what's the difference?
DrixxXo's user avatar
  • 21
0 votes
0 answers
59 views

What if an object is rotating near light speed? [duplicate]

lets say that we have a cube made of say 1kg, and using some means, managed to impart enough angular momentum to make it rotate at the speed of light or at least 99% of light speed. ignoring the fact ...
Shanmukha Evani's user avatar
0 votes
3 answers
56 views

Is the radius equal to length/radians? [closed]

Is the radius equal to the length/radians. Since the circumference is 2 pi times r and radians of an entire circle is 2 pi r should be equal to lentgh/radians I needed this proof to understand why we ...
Thedambamjam's user avatar
0 votes
1 answer
54 views

Rotating fluid shape with its own gravity

Hi almost every student knows the rotating bucket with a fluid problem as described here: Fluid in a rotating cylinder I wanted to do the same for a rotating fluid in free fall (like in the ISS) to ...
Vincent ISOZ's user avatar
0 votes
1 answer
68 views

Absolute Angular Velocity - How to use?

From my dynamics course, we were introduced to the so-called absolute angular velocity of a rigid body. Below is a short diagram: The following equation for the velocity of point P on a rigid body is ...
user393495's user avatar
0 votes
2 answers
76 views

Confusion about conservation of energy with translational and rotational energy

This simulation has me confused about the conservation of energy. If both blocks have equivalent mass, and the velocity of the COM is equal, then they have translational kinetic energy equal to $K_{...
Luther Grusovin's user avatar
0 votes
4 answers
83 views

Understanding how to measure angular momentum [closed]

In pure rotation, angular momentum is measured about the rotation axis. This angular momentum is measured with respect to that axis. Why do we consider it universal? It should change with respect to ...
Deepam Saxena's user avatar
4 votes
1 answer
99 views

Determining a direction/projection/heading for an object in 3D space after it has been rotated

I hope this is a good place to find an answer. Regardless, Worldbuilding looks like a great forum to follow. I'm not a math wiz and I've tried to tackle this problem many times over the past decade or ...
edasac's user avatar
  • 51
1 vote
1 answer
69 views

Which direction will the gymnastics tilt twist turn me? Figuring out rotation direction in torque-free precession

I'm trying to understand the physics of tilt twisting in gymnastics / trampolining, and I've run into a conundrum where theory doesn't seem to agree with practice, so I'm looking for where my mistake ...
Gabi's user avatar
  • 357
0 votes
1 answer
53 views

Contradicting approaches to deriving power needed for a flywheel [closed]

My problem involves a flywheel of moment of inertia, $I$. I would like the flywheel to start at rest and achieve a rotational velocity of $\omega$, within $t$ time. I see two approaches to the problem,...
Alex Vaughan's user avatar
1 vote
0 answers
26 views

Assistance in writing the rotational constraints of a spool, in rotational dynamics

I came across a very interesting problem involving rotational dynamics, from the series of Cengage Physics books, which was asked in an Indian competitive exam called KVPY. Write the constraint ...
Bongo Man's user avatar
  • 131
0 votes
0 answers
39 views

How to measure Angular Velocity observed from A non-stationary frame?

A stationary observer observes a rotating disc with radius 1 at angular velocy w. Let's say this disc is centered at origin in xy plane (all angular Velocity mentioned in this question is around the ...
infiNity9819's user avatar
0 votes
0 answers
45 views

Is angular velocity and angular acceleration independent of translating frame

[CONSIDERING ALL BODY RIGID] So think of a body which is rotating if I see it from a rotating frame,let's say with same angular velocity then the body will appear rest to the frame , so will have zero ...
Guess's user avatar
  • 91

1
2 3 4 5
27