A tag for questions about the mechanical interactions of rotating objects, including torque and angular momentum.

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3
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0answers
58 views

How is Temperature and Pressure related to when a tire rolls on the ground?

Actual observation: Here in Canada it is known that even when 'dry' snow is on the ground, and when a car drives over it that small amount of dry snow instantly becomes ice (NOT GOOD). Anyways as an ...
0
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0answers
24 views

The precession component in the direction of spinning

Is the precession increasing the rotation around the axis of spinning? w = (nutation) i + (precession component) j + (another precession component + spinning) k or to rephrase, is the precession ...
3
votes
1answer
108 views

Why isn't kinetic energy conserved in this rotational dynamics problem?

Consider a uniform rod which is spinning about an axis that goes through its centre, perpendicular to the rod itself. Two small rings are attached on the rod at equal distances from the centre. As the ...
2
votes
2answers
39 views

The way planets rotate and revolve [duplicate]

Why is that the all planets move in the same plane?(correct me if I'm wrong) Why not some of them in anticlockwise direction and others in clockwise direction?
3
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1answer
55 views

Parallel axis theorem: adding mass

I'm going through a worked physics problem and have a question about the parallel axis theorem regarding only adding mass while not changing is axis of rotation. Here is the problem: A physics ...
1
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2answers
67 views

Angular momentum changes depending on orign

Consider the image below where we have two point masses $m_1$ and $m_2$ with different masses which are rotating around a fixed axis with angular velocity $\omega$. If the origin is placed on the axis ...
2
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1answer
85 views

Change in acceleration due to gravity because of rotation of earth [duplicate]

The formula above is the equation for acceleration due to gravity when earth rotates. G is the original acceleration. Can someone explain how this formula came?
1
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1answer
70 views

Is moment of inertia numerically additive?

NOTE: The following argument is being made for square only, not any general shape. We have this square plate: From Perpendicular Axis theorem, $$I_1 + I_2 = I_z \\ I_3 + I_4 = I_z$$ Also, ...
0
votes
1answer
26 views

Why does this consider the center of mass instead of the end? (RIGID BODY MOTION) [closed]

A uniform rod of length L and mass M is free to rotate on a frictionless pin passing through one end. The rod is released from rest in the horizontal position. What is its angular speed when it ...
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2answers
35 views

Confusion regarding torque and centre of mass

When a body slides down a rough incline plane, why does $mg \cos \theta$ and normal reaction produce no torque? And why does $mg\sin \theta$ produce torque?
1
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1answer
46 views

Why centrifugal force results in a circularly rotating motion for a stationary object in the non-rotating frame

My doubt is the following: in a rotating frame of reference you have the centrifugal pseudo force. When you analyze and object in circular motion (due to a rope) in the rotating frame of reference, ...
0
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1answer
36 views

Angular momentum of a rigid body about any points

Is angular momentum about all points same if the body is rigid and is rotating/translating/rolling with a constant velocity? Why? No external force is acting on the body.
0
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2answers
38 views

What is the purpose of the directions for vector quantities such as angular velocity and torque?

Looking at just both angular velocity and torque, many other exhibit this same property. What is the purpose of and usefulness of having a direction that is in the Z-direction? (assuming that, in the ...
0
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3answers
45 views

In case of pure rolling, does the formula $v=r\omega$ holds only for a small instant of time?

For example, on a rough track when a ball rolls and is under smooth rolling, friction continues to act in the lower portion and so, torque acts along the centre of the ball. As per the formula: ...
1
vote
1answer
63 views

How far does the ball travel before pure rolling motion occurs? [closed]

A bowling ball is given an initial speed $V_o = 10 \text{m/s}$ on an alley such that it initially slides without rolling. The coefficient of friction between the ball and the alley is $\mu = 0.06$. ...
1
vote
1answer
17 views

Expressing 3D orientation in alternative to Euler angles for 3D rigid body dynamics

I was unsure whether it would be best to post this in Physics, Maths, or other forums, so please say if this question is suited better elsewhere. I am trying trying to create a physics engine for a ...
0
votes
1answer
33 views

How to find the angular acceleration (rotating reference frames)

If you chose the frame to rotate with $w_1$ instead of $w_2$, wouldn't the angular acceleration be $w_2 \times (w_1 + w_2)$? and it would have $+20 \jmath$ instead? Shouldn't the absolute ...
0
votes
1answer
36 views

How fast will a ball travel if spun around with a string then released? [closed]

It may seem like a stupid question, but I was wondering: If a ball with a mass of 50 kg was rotated from a string with a radius of 10m and a velocity of 100 m/s how fast will it be travelling when ...
0
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0answers
21 views

Considering rolling without slipping using axis at contact point with surface

For a ball rolling down a ramp without slipping, we can use $\Sigma \tau = I \alpha$ about two axes: an axis through the center of the ball, and an axis through the contact point with the surface. The ...
0
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1answer
27 views

In golf, is there a rotational mechanical advantage of using a thicker grip?

I was asked to migrate this question to the physics exchange. Ok, so many professionals are now using the new SuperStroke golf grips. I am basically thinking about the concept of a bigger grip, but ...
0
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0answers
31 views

How to calculate the equations of motion for a dipole in an electric field in three dimensions

I'm having trouble modelling a system, which I thought would be simple but has turned out to be quite complicated. The system is a charged sphere in an oscillating three dimensional electric field. ...
12
votes
5answers
3k views

Is there any friction between wheel and road?

Human beings invented the wheel to get rid of the friction between the wheel and the road. But were we able to reduce it to zero? Is there any residual friction? This question is about only the ...
0
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2answers
44 views

How does friction act in rolling motion? [duplicate]

In case of rolling, static friction at the lowermost point becomes zero once pure rolling starts. So how is that when we apply a constant force on the centre of mass of the spherical body (or any ...
-1
votes
1answer
48 views

Force required to rotate a rod around an axis [closed]

The problem I'm trying to solve is: How much force, momentarily applied to the rod, is required to rotate it around an axis by a given degree? Assuming there is friction applied at the axis (...
0
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0answers
23 views

What point is the torque on a loop in a magnetic field taken about?

I know that the torque on a loop kept in uniform magnetic field is given by $$\vec{\tau}=\vec{M}\times\vec{B}$$ where $\vec{M}$ is magnetic moment. Now, can I take this torque about any point in ...
0
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2answers
113 views

Moment of inertia of solid cube about body diagonal

How do I find the above mentioned moment of inertia? Steps I've tried: 1.) Triple integrations that proved to be to big. 2.) I noticed that the if we split a $2\times 2\times 2$ into individual ...
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0answers
31 views

Accelerometer reading in a uniform circular motion

Question - there is an accelerometer kept in a car moving in a uniform circular motion. The accelerometer is kept in such a way that the z axis points downwards, x axis is pointing towards centre of ...
3
votes
1answer
74 views

Why do throwing knives need to be balanced?

Indeed, unbalanced throwing knives are used, but I have read that balanced throwing knives are easier to use, because due to their geometric center being the same as their center of mass. Why would ...
0
votes
1answer
84 views

Rotation of fluid filled cylinders [closed]

Given two cylinders of same mass , one completely made out of solid metal and the other a hollow one which has been filled with a viscous fluid say oil. Both have the same mass.Now if they are placed ...
0
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0answers
26 views

Tangential Velocity of a Rotating Rod

I have the following question which has given rise to a doubt. Question: One end of a rod of uniform density is attached to the ceiling in such a way that the rod can swing about freely with no ...
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4answers
143 views

How is angular momentum conserved

from a classical perspective, what is it about angular momentum fundamentally that means it has to be conserved? Surely if I have a rod about a fixed axis and a moving particle hits the end it will ...
1
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1answer
30 views

Can a wheeled vehicle remain stationary on a water surface?

There are many field examples[1] of motorized, wheeled vehicles capable of staying on the surface of water. It appears that the requirement is sufficient "reverse-pressure" against the part of the ...
1
vote
1answer
53 views

Where to hit the pool ball such that it satisfies the given condition? [closed]

The question Where to hit the ball in such a way that after covering a certain distance it rolls back? You are given a pool ball and you have to find where to hit it such that it rolls back after ...
1
vote
2answers
55 views

How does this spool have an angular acceleration opposite to its acceleration?

Consider this spool. It rests on a rough horizontal force. The green lines are the ground, and a line parallel to the ground. The spool is pulled without sliding by the thread (with tension T), with ...
1
vote
1answer
38 views

Rotation with axle with unequally sized wheels

https://youtu.be/hwgjMPaKMiA In the above video, I have an assembly of two wheels of unequal radii connected via an axle. Now when we apply an external force anywhere on the axle, we see something ...
2
votes
1answer
56 views

Why does a top spin so well?

I know that the force of friction does not depend on surface area, but then why does a top spin better on a point rather than a region of larger surface area. For example, if I spin a top on it's ...
0
votes
2answers
100 views

Time period of a satellite close to earth

The time period $T$, of a satellite revolving around the earth and close to it is given by, $$T = \frac{2\pi r}{v}$$ where $v$ is the linear velocity of the satellite and roughly equal to $8\ \mathrm{ ...
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0answers
34 views

0G(No motion) scenario detection using Accelerometer and Gyroscope [closed]

I have a gyroscope and accelerometer which I am placing on the wheel of a bicycle to detect the 0G or standstill (when the bicycle exactly reaches to rest) of the wheel. I put the sensor at a R/2 ...
0
votes
1answer
38 views

why will two bodies rotate about their centre of mass if they do so for their mutual attraction

If two bodies rotated because of their mutual attraction. They will do so about their centre of mass. Why is that ? I understand that if there is no external force then the centre of mass must not be ...
0
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1answer
40 views

Kinetic energy during 1 minute - wrong? [closed]

I've come across this IEEE paper whilst researching for a project I've undertaken regarding a bicycle generator. This paper concerns an exercise bike powered electric generator. Essentially they have ...
1
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0answers
30 views

Doubt in a question about a body rolling up a ramp [closed]

I encountered a question in this year's paper of an exam, and I am in confusion. The question says: A body with mass $m$ and radius $R$ and rolling without slipping with speed $V$, moves up a ...
0
votes
1answer
63 views

Why do we need theorems like **Parallel Axis Theorem**

In rigid body pure rotation, quantities like $\omega, \tau, L, I, r_i$ (symbol with usual meaning) are axis dependent. Assume rigid body to be sphere rotating about the axis passing trough the center. ...
0
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2answers
47 views

Why don't we include angular acceleration while calculating net acceleration for a particle moving in a circle ?

When we calculate net acceleration of a particle It is the vector sum of the centripetal acceleration and the tangential acceleration (if any) however why don't we also consider adding angular ...
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0answers
17 views

Modelling Rotational Motion using Linear Accelerometer [closed]

I am using a 3 axis linear accelerometer on the wheel of a car at position $R/2$ (Where $R$ is the radius). Now i am modelling the equation which i will be getting at the output of the accelerometer. ...
0
votes
1answer
89 views

Moments of Inertia (Calculus Application)

Hi so here's the problem I'm working on: Consider a 2 meter-long rod with linear mass density $\lambda(x)=x$ kg/m, where $x=0$ corresponds to one end of the rod. (a) Determine the centre of ...
0
votes
1answer
41 views

Does a weight attached to a string over a spinning pulley count as a transfer of kinetic to rotational energy?

More specifically, if I had a weight hanging on one end of a pulley at some height h (the other end of the string continues onto another pulley) and I let it go, would the kinetic energy gained from ...
0
votes
2answers
86 views

How does a cyclist moves the center of mass of the cycle-cyclist system?

Consider the image shown below, In the left diagram the centre of mass of the system lies upon the perpendicular from the point of contact. But in the right diagram the centre of mass has shifted ...
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3answers
61 views

What is the difference when we measure torque/angular momentum about a point and about an axis?

When do we measure torque about an axis and when do we measure torque about a point?Whats the difference? I tried searching this on google but did not get satisfactory answer.
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0answers
31 views

Physical significance of direction of rotational variables

When discussing rotational quantities, the direction of such vectors corresponds to the axis of rotation, and not he actual direction of rotation(for example, while we use torque in clockwise and ...
0
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0answers
35 views

Why do linear momentum and angular momentum have to be conserved in ground frame only?

According the Newton's second law of translational and rotational motion respectively if the net external force /torque acting on a body is zero then the linear/angluar momentum is a constant . So ...