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

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0
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2answers
48 views

Direction of static friction in inclined rolling motion

I can't seem to understand in which direction static friction faces for inclined plane motion with rolling motion. This considers rolling motion without slipping, how do i find the direction of the ...
9
votes
4answers
3k views

Hamiltonian is conserved, but is not the total mechanical energy

I wondering about the interpretation for the energy difference between the Hamiltonian and the total mechanical energy for systems where the Hamiltonian is conserved, but it is not equal to the total ...
0
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2answers
39 views

What are our limitations on spinning a baseball sized 5 kg sphere to really fast speeds?

I know the limitation of the ball being able to hold itself together, lets assume that would not be an issue. If we were to apply a constant force over long enough time would anything short of the ...
24
votes
7answers
3k views

If I toss a coin, vertically, on the surface of Mars, will it land back in my hand?

When I toss a coin in Mars, is the planets atmosphere rare enough that I'd rotate with the planet (at its angular velocity), but not the coin?
0
votes
2answers
245 views

A lever arm-definition question

My question is regarding Torque, and specifically the definition of the lever arm. As far as I've understood, the lever arm is the line perpendicular to the line of action to your reference point. ...
2
votes
0answers
39 views

Man walking on the rotating platform [closed]

The problem is: The solid cylindrical platform with mass $M$ and radius $R$ rotates with angular frequency $\omega$. On the edge of the platform there is a standing man with mass $m$. Then man ...
1
vote
1answer
21 views

Four bar linkage moment transmission

The question is. I know the angular velocity of $d$ after applying dynamic mechanics and the constant angular velocity of $b$ of $2\pi\ \text{rad/s}$ and I know the input moment of the power source ...
1
vote
1answer
58 views

How do I handle elastic contacts in a simulation with friction [closed]

I'm trying to simulate a wheel as it hits the ground. Problem 1 Suppose a disc is dropped from a height. It has initial velocity of $-x,-y$ caused by throwing and gravity. It has no initial angular ...
1
vote
1answer
68 views

Conservation of angular momentum during rolling

A disk having initial angular velocity $\omega$ is gently placed on a rough horizontal surface. What is the angular velocity of rotation when pure rolling starts? I've tried applying conservation ...
0
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0answers
34 views

Simple Rotating frame of reference

I have a car moving in straight line with certain time-varying acceleration and there is another car moving in a curvilinear way along some curved path with some time-varying acceleration. The ...
0
votes
1answer
31 views

Is a rotor balanced at constant angular velocity?

I have an asymmetrical rotating part. It vibrates its housing and emits audible noise. I need to add weights to ensure smooth rotation. However, I am constrained in which regions I can add ...
-1
votes
1answer
27 views

Understanding the constraint of tension with a rigid body

I want to know why doesn't $T_1 = T_2$? I think its probably because of the Pulley but still aren't the Tensions Equal but opposite in direction.
1
vote
1answer
154 views

Rotation motion like the number 8

I'm a college student majoring in culinology and I'm trying to find out the reason or method of the number 8 motion. Responses doesn't have to be in culinology examples, but that would be a great help ...
0
votes
1answer
39 views

A sphere rolling down a plank - an error in calculating its energy

Consider the following situation: A sphere with radius $r$ rolls down a plank which forms an angle $\theta$ with the horizontal axis. The starting hight of the centre of mass is $h$. We assume that ...
1
vote
1answer
88 views

Why does the pen does not move straight?

If i put a pen on a table in its horizontal position and then i try to move it horizontally by giving it a small push, so that it would fall off a table, i expect it to move horizontally but my pen ( ...
7
votes
3answers
629 views

Why don't we talk about angular momentum at all in fluid mechanics?

People usually talk about similar (or maybe not?) things like vorticity or enstrophy in fluid mechanics, but no one talks about angular momentum, why?
0
votes
2answers
943 views

Tricky conceptual question: ball sliding and rolling down incline [closed]

We all are familiar with the classic ball rolling down the incline exercise in rotational dynamics. Here is quite a tricky conceptual problem: You have an incline of fixed height, but the angle ...
4
votes
1answer
579 views

If a bullet is fired vertically upwards, when it comes back does it fall to the same spot? [duplicate]

What I'm basically asking is that if a body is projected with sufficiently high velocity so that it doesn't escape from the earth's gravitational field but reaches an appreciable height with respect ...
0
votes
0answers
34 views

A problem regarding translational & rotational motion

Let a force $F$ be applied to a body of mass $m$ for time $dt$ where the line of action passes through the centre of mass. This means that the change in momentum will be $Fdt$, and the change in total ...
2
votes
2answers
1k views

Moment of inertia of a coin [closed]

I have a a coin infinitely thin, rotating along the diameter. How to derive the formula for it's moment of inertia passing through the diameter. I was suggested to use the surface density and ...
0
votes
1answer
122 views

Rotational dynamics

In studying rotational dynamics of a rigid body, I can't seem to understand why you can solve the problem correctly only using certain points in a body and not all? Angular momentum and torque leads ...
0
votes
0answers
45 views

What is the derivation of $r*F=Iα$? [duplicate]

Please give me the derivation of the formula r*F=Iα for extended body. where, F=applied force r=distance between point of rotation & point where force is applied I=moment of inertia of the body ...
0
votes
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 ...
1
vote
1answer
56 views

Gyroscope precession

I have a system diagrammed and explained in the image below. Experimentally I believe the wheel will rotate around the pivot point where the cable is attached in a counter-clock motion if ...
3
votes
0answers
56 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 ...
4
votes
3answers
5k views

Which force makes a wheel roll down the hill? What causes friction?

A wheel rolling down a hill has two axis of rotation. One is where the center or mass is and the other is the point of contact with the surface which acts as a fulcrum. I was trying to understand ...
0
votes
1answer
148 views

Rigid Body Dynamics - Calculating Rotation of an Object

I've looked everywhere and I can't quite find a concise answer, especially due to my limited knowledge and understanding of terminology. I found something called Rodrigues' Rotation Formula that ...
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
38 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
votes
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
vote
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 ...
0
votes
3answers
1k views

What rotates a door : torque or centripetal force?

I can realize that they are different, but can't understand what actually creates a rotational motion. Rotational motion doesn't mean just moving in a circle. There must be rotation of the position ...
1
vote
1answer
67 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, ...
2
votes
1answer
78 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?
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 ...
0
votes
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?
55
votes
6answers
4k views

Is there a way for an astronaut to rotate?

We know that if an imaginary astronaut is in the intergalactic (no external forces) and has an initial velocity zero, then he has is no way to change the position of his center of mass. The law of ...
2
votes
1answer
159 views

Lagrangian in rotating reference frame

I have a homework question I am working on, and I'm stuck on the last term in this proof. The problem states: Question: Consider a primed set of axes coincident in origin with an inertial set of axes ...
0
votes
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 ...
1
vote
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
votes
1answer
33 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
votes
3answers
43 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: ...
15
votes
8answers
6k views

What is the electric field generated by a spinning magnet?

Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
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
16 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
32 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 ...
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 ...
3
votes
3answers
2k views

Does a toy top weigh less when it is spinning?

I am under the understanding that a toy top will weigh less when it is spinning. The Russians made a spinning type transport back in the 70s to lessen its payload over the tundra. Is this an effective ...
0
votes
0answers
20 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 ...