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

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Question in rotational mechanics [on hold]

Question number 14. This question is from coaching material for the chapter rotation. For a cylinder, moment of inertia I=1/2MR^2 How do I apply this data? Is it to do with conservation of ...
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1answer
34 views

How do you define the total rotational energy of an object?

This problem arose when I was applying a conservation of energy argument to a mechanics problem, (a spinning coin on a table) and wasn't sure how to define the total rotational energy of the coin. At ...
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1answer
10 views

what is intertia tensor for tapered cylinder (solid and with separate inside and outside radii)

I need the inertia tensor for tapered cylinders, both solid and hollow, and if possible with independent inner and outer radii on the x and y axes (so the cross-sections of the cylinders can be an ...
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44 views

Total Energy of Inverted Pendulum

I have to find the total energy $V$ of an inverted pendulum (rod). The following parameters and their values are given: Mass $m$ and length $l$ of the pendulum $\theta$ as the angle of the ...
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2answers
43 views

How to treat an exercise about the rotational acceleration during a throw?

Because I am studying on my own, I don't have anyone to talk to about this when I don't understand, and I was wondering if someone could help me with a concept in rotational kinematics: At the ...
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111 views

Am I right in my understanding of angular motion?

Here is what I've understood about angular motion: If a force is applied at the center of mass of a rigid body, it will undergo pure translational motion. If a force is applied away from the center ...
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3answers
182 views

Confusion regarding rotational motion!

Let us assume I have a rod of some mass m, moment of inertia I, length l and center C. If I apply a force F on C for a duration of time t, it will accelerate forward. If I apply it elsewhere, the ...
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2answers
137 views

At what point does force stop translating an object and start purely rotating it? [duplicate]

At what point (or distance) from the axis of rotation, does force applied on a rigid body stop translating and purely rotating the body? Can such a point even exist? Does the body always have to ...
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1answer
43 views

Calculating Angular Acceleration of a Rolling Object

A bowling ball of mass M = 6.50 kg, radius R = 10.0 cm, and moment of inertia I = $(2/5)MR^2$ is given an initial center of mass velocity $v_0 = 3.00 m/s$ that is parallel to a horizontal surface. ...
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1answer
35 views

Angular velocity formula for a particle?

I know that when the motion of a particle is circular about the origin then: $$\vec v=\vec \omega \times \vec r$$ But that this does not hold for any motion with a radial as well as tangential ...
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1answer
44 views

Variable Gear System [closed]

I have a variable speed gear system with 4 primary parts. I need to find the relationship between input rotational speed (wi) to output rotational speed (wo). Fig. 1 shows three of the primary ...
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77 views

Why did Feynman tell “we cannot locate earth's angular position, but we can tell that it is changing”?

I was reading "Symmetry in physics" by Feynman, where he wrote: If we perform sufficiently delicate experiments, we can tell that the earth is rotating, but not that it had rotated. In other ...
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34 views

Kinematics of a differential drive robot

(I am reposting here a question I asked on stack overflow, since it actually sits right in between programming (modeling of 2D physics) and physics proper (kinematics). I think I have the physics part ...
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1answer
33 views

Starting point for a derivation of fictitious forces

I came across this expression at the start of a derivation of fictitious forces: $$(dA/dt)_L = (dA/dt)_R + \omega \times A$$ Where the $L$ subscript refers to the laboratory (inertial) reference ...
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1answer
55 views

Is this movement possible?

My friend and I were arguing over some random facebook shared video. On this video, one guy throws up a rotating stick then, while it rotates on air, he kicks through it. Is it even possible? Or is it ...
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1answer
57 views

Representation Of Linear Velocity as Cross Product

Why is linear velocity represented as cross product of angular velocity of the particle and its position vector? Why not vice versa? (Consider rigid body rotation)
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imbalance calculation something with f m r in calculation [closed]

A road wheel has a mass of 10kg. It is found that its centre of mass (or gravity) is offset from its centre of rotation by 2mm. Calculate the out-of-balance force acting on the wheel when the vehicle ...
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3answers
105 views

Does circular motion cause centripetal force OR does centripetal force cause circular motion?

Does circular motion cause centripetal force, or does centripetal force cause circular motion, or are they both occurring hand in hand together instantaneously? One more question: If I project a body ...
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1answer
38 views

How much energy would it take to stop Earth's rotation on its axis?

I see a lot of questions regarding situations what would happen if the world would stop spinning. This got me to wondering how much energy it would actually take to stop the world from spinning.
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2answers
31 views

Conceptual Understanding of Reference Frames correct?

The problem is as follows: A cart has a velocity to the right. There is a wheel on the cart (fastened to it). Determine the angular speed of the wheel so that the velocity at a point on the top of ...
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4answers
842 views

Puzzling : Relative motion of two points on a rotating disc

Consider two points on a radial line for a rotating disc. One point, $A$, is at the circumference and the other, $B$, is at distance $R/2$ from disc's centre. Relative velocity of $B$ w.r.t. $A$ ...
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1answer
96 views

Basic question about angular momentum

I've learned that the angular momentum of an object rotating about a fixed axis is $I \omega $. Also, in absence of external torques, $I_1 \omega_1 = I_2 \omega_2 $ (meaning, two different events). I ...
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Trajectory of a boat given by $$r=\frac{d sec(\alpha)}{(sec\alpha + tan\alpha)^{V/V_{R}}}$$ [closed]

I need some help with this problem, I've tried using polar and cartesian coordinates but I dont know how to get the trajectory (I've already obtained the position, velocity and acceleration vectors as ...
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0answers
40 views

Rotational energy with moment of inertia tensor

Some objects have a single moment of inertia value while others like ellipsoids have a tensor, if I wanted to work out the rotational energy of an oblate spheroid rotating around its z axis could I ...
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2answers
97 views

Instant centre of rotation for two connected gears

The two gears are have the angular velocities $\omega_1$ and $\omega_2$ respectively with respect to $Oxyz$. The task is to determine the angular velocity $\boldsymbol{\omega}$ of the arm ...
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1answer
92 views

If a car moves at a certain speed, how fast is its wheel going?

Say in a given instance a car moves with speed $v$ and consider any wheel of the car. How fast is it going? Is it the case that the center of the wheel moves at the same speed as the car i.e. $v$? Why ...
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1answer
41 views

Kinetic energy for rotating round body having its COM not at the centre

Say I have a round object, whose center of mass is NOT in its center. This can be caused due to a hole or non uniform distribution of density. The object rolls on the ground with velocity of ...
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1answer
58 views

Computing the angular momentum in spherical coordinates [closed]

How to compute the angular momentum of a particle in spherical coordinates? It's given by: $$x_1=r\cdot\cos(\phi)\cdot\sin(\theta)$$ $$x_2=r\cdot\sin(\phi)\cdot\sin(\theta)$$ ...
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2answers
162 views

Rolling as pure rotation

In my book the following statement was written and I didn't understand it well. Can anyone explain it in a more simple way? Figure 11-6 suggests another way to look at the rolling motion of a ...
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3answers
103 views

Uniqueness of the angular velocity

Let us consider the most general motion of a rigid body. Two arbitrary points of the body, $i$ and $j$ must not change their distance $d_{ij}$ during motion. Therefore,$$(\vec{r}_j - \vec{r}_i)^2 = ...
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1answer
73 views

How to calculate a rotating (and constantly decelerating) wheel's angle and speed at a given time in the future? [closed]

So imagine a wheel (a bicycle's wheel) that's spinning slower and slower (because the bike brakes). The time it takes for the wheel to complete one revolution increases in a linear way. Say it starts ...
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3answers
2k views

Centripetal acceleration units

I perform some basic calculation for circular motion. Formulas we get from school are: $v$ - Linear speed with the units m/s $r$ - Radius of curve in meters $\omega$ - Angular speed with the units ...
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1answer
60 views

Why is the Earth self-rotating? [duplicate]

What drives this happen? Would it be the internal energy or by an external force? I did try to Google the answer, but could not find a good one.
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1answer
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How do I transform onto a relativistic rotating frame of reference?

In classical mechanics, the usual formula to translate the evolution of a quantity as seen from an inertial frame of reference to a rotational frame is: $$\frac{d \textbf{A} }{dt} \vert_{Inertial} = ...
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1answer
28 views

Making water spin a wheel [closed]

Let's say that I have a wheel with 8 symmetric arranged rectangular plates of area $A$ and the water, with density $\rho$, in the river it moves with $v\: \mathrm{m/s}$. How do I calculate the ...
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2answers
452 views

Torque and Pulleys [closed]

I have the solution to the problem below, however I approached the question differently than my professor and I do not understand why my answer is different. Can someone help explain where I'm ...
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1answer
42 views

Determine coordinate system for rotating wheel

I am having trouble writing down the coordinate systems for a problem. In particular, I'm not sure how to figure out the translational acceleration of the moving coordinate system relative to the ...
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1answer
55 views

Why falling camera/objects rotate and then stabilize?

I was going to ask something very similar to this question (which hasn't been answered). Basically a camera fell from an airplane and it began to rotate (maybe because initially it was put in rotation ...
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1answer
64 views

What role does inertia play in determining how long an egg rotates?

There are two identical eggs boiled egg and raw egg, both are rotated with same angular speed. Which one will come to rest earlier? I have read this question, but it discuss more about friction and ...
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34 views

Problems when a disc is rotating at extreme speeds (theory)?

I was wondering the problems that would occur (aside from mechanical friction), when a disc rotates at high angular velocity. Is centripetal force an issue if high torque is applied on a disc ...
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2answers
47 views

Rigid bar on the floor of a rotating space station

I read this in a comment to an answer in physics.stackexchange.com. The comment was An easier method might be to just place a straight, rigid beam on the floor. If you find the floor is concave, ...
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1answer
98 views

Why do some objects tend to change their axis of rotation while rotating?

This question struck me a few minutes back, I was at a table with a pear. It was more narrow than round.I proceeded to rotate this pear in one swift movement. It rotated for a few seconds, and ...
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1answer
57 views

Rotational mechanics - ball climbing a step

A wheel of radius, $R$ and weight, $W$ stands in front of a step of height, $h$ where h is less than R. What is the least horizontal force $F$ which must be applied at the axle of the wheel to allow ...
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3answers
201 views

If angular velocity & angular acceleration are vectors, why not angular displacement?

Are angular quantities vector? ... It is not easy to get used to representing angular quantities as vectors. We instinctively expect that something should be moving along the direction of a ...
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1answer
146 views

Does rotation increase mass?

If an object is rotated on its axis near the speed of light would its mass increase? Normally if the object was moving (in relationship to the Earth for example) I would agree that its mass would ...
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1answer
155 views

How to calculate rotational velocity from torque [closed]

Problem as stated: A radio transmission tower has a mass of 80 kg and is 12 m high. The tower is anchored to the ground by a flexible joint at its base, but it is secured by three cables 120 ∘ apart. ...
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2answers
201 views

Why is angular velocity of any point about any other point of a rigid body always the same?

I have the following question regarding an ideal rigid body. Firstly, is it always true without any exceptions that the angular velocity of any point about any other point on a rigid body is always ...
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translational energy levels

My textbook says translational energy level is so closed, and it basically covers the whole EMR spectrum, so any temperature beyond absolute zero is high enough for molecules to have translational ...
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1answer
590 views

Rolling with slipping [closed]

A tundra buggy, which is a bus fitted with oversized wheels, is stuck in Churchill, Manitoba, on slippery ice. The wheel radius is 0.86 m. The speedometer goes from 0 to 27 km/h while the buggy ...
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1answer
32 views

A block is rotated with $ω=a\cdot t$ [closed]

A block of mass $m$ lies on a table. The coefficient of friction between the table and the mass is $μ$. The table is rotated around where the following relation holds: $$ω=a\cdot t$$ (where t is ...