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

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28 views

Does vehicle tire mass effect efficiency?

This question has an interesting origin: A tire salesman was recommending tires (aka tyres) for a highly fuel-efficient vehicle. He said the vehicle was light (compared to most production cars), and ...
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1answer
38 views

Problems with moment of inertia [closed]

I totaly confused with these two problems can someone give any hints, or just final formula i get tired with it. Find the velocity of (a) a cylinder and (b) a ring at the bottom of an inclined plane ...
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2answers
30 views

Rotation of join of two different rods when one is rotated [closed]

Two cylinders A and B made of same material and having same length of radii $r$ and $2r$ are soldered coaxially. The free end of A is clamped and the free end of B is twisted by an angle theta. The ...
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1answer
54 views

Impulse and momentum on a system of three particles (equilateral triangle)

I found this exercise on a textbook which provided solely the description of what is happening and the answers with little explanation. The solution being provided, I am mostly interested in ...
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1answer
36 views

Velocity of a body in a pulley problem involving a spring fixed to the ground

So the picture shows the whole situation. My question is, how do you find the velocity of the object after it had descended 10 cm (0.1 m) ? Pulley's radius 0.2 m, moment of inertia 0.2 kg/m I ...
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1answer
60 views

Why does a force parallel to the axis of rotation do not produce torque? [closed]

One explanation can be that Torque is a cross-product (r x F). I want to know what is its physical interpretation.
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2answers
42 views

Conditions to impose for accelerations in systems of rotating pulleys [closed]

I do not understand completely how do rotating pulleys with ropes (that do not slip) work. Besides the equations of motions, which are clear to me, some conditions on the accelerations are needed to ...
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1answer
42 views

Does the centrifugal force affect stationary objects as seen from the inertial reference frame?

If an object is moving at the same speed as a rotating/accelerating frame of reference it's in contact with but in the opposite direction (making its displacement zero), would such an object be ...
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2answers
106 views

Difference between potential centrifugal energy and rotational/kinetic energy

I'm having troubles to understand the difference between kinetic energy and potential centrifugal energy in some situations. I make an example where I am confused. A object moves on a rod attached ...
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1answer
46 views

What is the relationship between $W_1$ and $W_2$? [closed]

I have a model which schematic is in the linked picture. Blue $A$ and $B$ are rotational joints, black and red shapes are rigid elements. $I_1$ is moment of inertia of black and red elements combined ...
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0answers
52 views

Rotating rigid rod in empty space [duplicate]

To begin, we assume there is a rigid rod in empty space which has no rotation with respect to the fixed stars. The frame of the rod is now an inertial reference frame, say $F$. 1) The rod now has a ...
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1answer
51 views

If a disc is rolling on a surface, how do you verify that no slip occurs? [closed]

If I have the values for the coefficient of static friction (0.1) and all the other variables, how do I verify that no slip occurs?
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4answers
161 views

Why does Torque exist?

Specifically, why does force increase with the moment arm? What about making a perpendicular force farther away from the axis of rotation increases it? How does the moment arm cause that?
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1answer
49 views

Does the rotational form of Newton's second law always hold?

Does the equation, $$\vec \tau=I\vec \alpha$$ (rotational form of the second law) always hold? If not, in what conditions does it hold true?
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0answers
43 views

In pure translation why the body does not exhibit rotation only and only about the CM?

Suppose I have a rod in pure translation as shown in the picture with some constant acceleration. The two forces $F_1$ and $F_2$ act as shown. So clearly due to the definition of pure translation ...
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1answer
27 views

What kind of motion is caused by nonzero torques about two parallel axes?

Say on a rigid body there are non-zero torques about two parallel axes. About which axis does it acquire a angular acceleration? I'm looking for a mathematical explanation.
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0answers
50 views

Will future spaceships for very long distance rotate?

I have seen in the movie Interstellar and The Martian they use the model of spaceship which rotate around it's axis. This is the spaceship model from Interstellar. This is spaceship model from The ...
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1answer
73 views

Cylinder on an accelerated rough plane [duplicate]

The following figure shows a cylinder resting on a rough horizontal rug that is pulled out from under it with acceleration $a$ perpendicular to the axis of the cylinder. What is the motion of ...
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1answer
40 views

Rotating movable pulley [closed]

I'm trying to understand how a movable pulley of mass $m$ and radius $r$, that rotates and doesn't slip actually works. Consider the picture, if a force is applied at the free end of the rope, are ...
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3answers
193 views

Conservation of angular momentum in broken pendulum

I'm having troubles in understanding the correct way to use the conservation of angular momentum. Consider the pendulum in the picture with a neglegible mass rope and a slender rode of mass M and ...
2
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2answers
241 views

Reaction to gyroscopic force [duplicate]

Just like the reaction of the weight of a body is a force acting on Earth towards the body, where and in what direction does the reaction of a gyroscopic force act?
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3answers
60 views

Net force for circular motion

So today my physics teacher was telling us that the net force when discussing circular motion was actually the centripetal force. He didn't go further and I would like to know if there's any proof to ...
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2answers
68 views

How to find speed of rotation of gears from kinetic energy of falling body?

A pulley is fitted to the first driven shaft of compund gear train. Last driven shaft of gear train(gear 8) is fitted to the 12V DC generator (6W).Now to the rope extension at the one end of the ...
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1answer
36 views

Clarification on what inertia and area moments?

This is something I have never understood despite applying the formulas in many classes. What I'm hoping to find here is some clarification. My understanding is that the first moment of inertia is ...
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0answers
86 views

Why do trees sway?

Resonance can also occur in three dimensions (such as wind induced swaying) I tried to make a free body diagram (I know it is terribly wrong) to find the forces that causes the tree to undergo ...
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0answers
22 views

rotating jars and centripetal force

why does water rise up the sides of a jars that are spun in a circle. How does the centripetal force act on the water making it move away from the center of the circle? Also how does speed affect the ...
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1answer
51 views

Parallel axis theorem proof?

First, I thought theorems do not have proofs. Anyway, for parallel axis theorem, I was given that the addition of translational kinetic energy and rotational kinetic energy proves the parallel axis ...
2
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1answer
47 views

Torque on a right angle triangle [closed]

I am attempting a question regarding the torque on a right angle triangle. The triangle is pivoted along the adjacent axis, there is no force acting on the opposite side, however there is a 12N force ...
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1answer
41 views

Rotational motion: A cylinder, sphere and hoop rolling down a ramp [closed]

I have a question about comparing different objects in rotational motion. In this scenario: A cylinder (with moment of inertia = $\frac{1}{2}MR^2$), a sphere ($\frac{2}{5} MR^2$) and a hoop ($MR^2$) ...
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0answers
15 views

How to determine the right motor to rotate things? [closed]

Me and my teammates are trying to produce a motorized rotating bench. we want to rotate the bench to the other side if one of them get wet by the rain. we are currently doing the proposal for our ...
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0answers
15 views

Relevant Archemidan Spiral Theorems: An Enquiry

Basically what I'm doing is investigating the solar wind's outflow. As part of this investigation is included a fairly crude application of a more complex outflow solution to that of basic archemidian ...
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0answers
42 views

Converting torque to angular velocity

Given the torque of a system, is it possible to convert this torque to the angular velocity of the object? I calculated the torque exerted by wind on a blade, however, now I need the RPM. To get the ...
3
votes
2answers
86 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 ...
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1answer
35 views

Rolling cylinder on frictionless inclined plane

A cylinder is kept on frictionless inclined plane. Why it does not roll (it slides only), although torque with respect to contact point is working on it (due to component of weight parallel to ...
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3answers
337 views

Acceleration of body rolling down inclined plane

Acceleration of a body rolling down an inclined plane is given by: $$\frac{g\sin\theta}{1+\frac{k^2}{r^2}}$$ $g$=acceleration due to gravity $\theta$=angle of inclined plane $k$=radius of gyration ...
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1answer
41 views

Where does the formula for the moment of inertia come from?

I think I 'understand' the concept of moment of inertia, but I don't see why it is proportional to r^2 (for a given point). Is the equation just empirical?
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2answers
69 views

Why do tires with low air pressure experience more friction?

How does tyre pressure affect the frictional force on a tyre even though friction is independent of area of contact? And how does one analyze or calculate this friction?
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2answers
52 views

Does orbital motion cause rotation?

Assume the moon was flying freely in space, and not rotating at all. If if then happened to pass earth at just the right distance and velocity to fall into orbit, would its absolute rotation be ...
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0answers
23 views

Angular velocity in body frame to displacement in lab frame?

For the case of a freely spinning symmetric top (no gravity), I derived the following equations, where $\omega_i$ is the angular velocity about a body-fixed axis: $$ \omega_1 = w_1 \cos (w_3 t) $$ $$ ...
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1answer
70 views

What happens when one uses a blender in zero gravity?

I was recently told by a friend that using a blender type apparatus in a zero gravity environment will act like a centrifuge instead mixing properly. Is this the case? Furthermore, can anyone provide ...
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0answers
76 views

Why did Einstein allow unphysical objects in his 1906 paper on $E=mc^2$?

In the first part of this paper, Einstein considers a "rigid cylinder", "massless cavity", as well as a "massless carrier mechanism" that is used to transport the massless cavity. These hypothetical ...
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3answers
97k views

Linear acceleration vs angular acceleration equation

I'm learning about angular velocity, momentum, etc. and how all the equations are parallel to linear equations such as velocity or momentum. However, I'm having trouble comparing angular acceleration ...
0
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1answer
29 views

Which force acts as centripetal force on gyroscope?

I think I have understood gyroscope in terms of angular momentum and how the torque of gravitational force moves it the way it does. Also I understand the direction in which it would move: What ...
0
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1answer
30 views

Is there no rotational mechanics for non rigid body? How do we deal with such situations in real life?

I am in 12th grade right now. We have a chapter on Rotational dynamics in which it is clearly stated that it is for rigid bodies. I understand that, Moment of Inertia will remain constant only for ...
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5answers
114 views

If I push or hit an object in space will it rotate or move along a straight line?

If I push or hit an object in space (vacuum and no gravitation) in direction what is not going trough its centroid, will it rotate or move along in straight line? I expect that on earth it will ...
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1answer
40 views

Please help me with this doubt from rotational dynamics

Torque to a magnetic field on a current carrying loop is same with respect to any point in space,is the same true for all force couples acting on any body?
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2answers
1k views

Angular momentum with respect to the centre of mass

I have been told [Warning: I leave this because it's what I asked and allows to understand the dialogues in the comments, but Azad, whom I thank, has pointed that the formula does not hold in general ...
0
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1answer
33 views

How to apply torque impulse

In the below question, can we apply conservation of Angular Momentum? If not, why? Moreover how do we apply Torque impulse to the system ? The contact force between the cylinders will be normal to ...
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0answers
27 views

Does a potential of interaction produce also torque?

I have a system of particles (spheres with masses and radii), with $6$ degree of freedom (they are free to move and rotate as they wish). Between each couple there is an interaction potential $V(d)$, ...
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2answers
3k views

Finding angular acceleration from torque

We have to analyze this video Givens: An applied net torque due to the wind on the windmill is equal to 1500 N*m. Each (of the 3) propeller props weighs approximately 45 Kg and has a Moment of ...