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

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-3
votes
0answers
30 views

Force applied to the rod [on hold]

How much force is applied to the other end of the rod the moment you cut the string? (g=10m/s^2)
3
votes
2answers
23 views

Force applies to sphere not on center of mass?

Is this true: When force is applied to a sphere NOT on center of mass (COM) then the sphere will move the same way as when force is ON center of mass, because the sphere is symmetric in every ...
-1
votes
0answers
52 views

Frequency's relationship to Angular velocity? [closed]

I have an issue regarding the concept of getting the angular velocity. I know that angular velocity relationship to frequency is w=2π*f, however I have a problem where a right circular cylinder with ...
0
votes
0answers
37 views

Period of a Neutron star? [closed]

I need help understanding this concept of rotational motion. I have a problem that uses a star in which the star has a radius initially of 7*(10^7) km and it is treated as a solid sphere(which means ...
-3
votes
0answers
41 views

Kinetic energy of a suspended mass from an overhead crane [closed]

I am using Lagrange's method to formulate the equation of motion for a 3D overhead crane that is shown below: For the formulation of the kinetic energy for the payload (suspended) mass. I have seen ...
-2
votes
0answers
24 views

Body Angular Velocity

I'm working with rotation matrices and body angular velocities and got a bit confused. I'm doing a yaw, pitch, roll rotation like here $$ \begin{bmatrix} cy & -sy & 0 \\ ...
-1
votes
0answers
16 views

dc motor rotational kinetic energy [closed]

Rotational Kinetc Energy of an armature in left DC motor is given as: $\frac12n^2J_m(\dot\theta_l-\dot\psi)^2$ where n = Gear ratio $J_m$ = DC motor inertia moment $\theta_l$ = left wheel angle $\psi$ ...
2
votes
0answers
67 views

Translational acceleration due to rotation

Sorry for boring you, my friends. I am haunted by re-deducing an expression of translational acceleration in ANSYS theory reference about acceleration effect. It takes the form of: $$\lbrace a_t^r \...
0
votes
1answer
111 views

Elemetary Rotations -imagining differential rotations - intitutive proof of such rotations being vectors

I was reading and extract from "Fundamentals Laws of Mechanics", 1980, by I.E Irodov, § 1.2. 'Kinematics of a Solid' and came across this insane text where the author asks me to imagine a 'solid ...
1
vote
1answer
29 views

Rolling motion of a rigid object

I have the situation described in this picture I know the speed of the ball at the top of the loop ($v_{top} = 2.38 m/s$), and I have to demonstrate that the ball does not fall from the track at ...
1
vote
2answers
50 views

Can a system's internal forces change the system's motion?

Let say the motor makes the two rigid body rotate as a same velocity. (they rotate the opposite direction) then the Net force of the motor is 2Fsin(Theta). The acceleration of the motor is 2Fsin(theta)...
0
votes
2answers
57 views

is curvilinear motion really a type of linear motion?

Let us consider any arbitrary curve except a straight line in the Cartesian coordinates. From the perspective of the particle tracing the curve the motion can only be linear. But from the point of ...
-1
votes
1answer
32 views

The motion of a ball on a spinning turntable [closed]

https://www.physics.harvard.edu/uploads/files/undergrad/probweek/sol21.pdf I'm having some trouble understanding the logic going on in the solution given in the paper above. Particularly in equation (...
-2
votes
2answers
55 views

Force at the centre of gravity [closed]

If we somehow apply a force direct to the center of gravity (existing inside an object ) , does it increase the angular velocity of a rotating object as it does in normal case ?
0
votes
2answers
23 views

The direction of frictional force in circular turning

Why does the frictional force in case of circular motion point towards the center even though the motion is tangential to the radius?
-1
votes
1answer
64 views

Why is angular acceleration of a pendulum always negative?

I was trying to derive using the Lagrangian the equations of motion of a simple pendulum under the influence of gravity. Eventually, I was brought to this conclusion: $$\alpha = -(g\sinθ)/l$$ where $\...
0
votes
1answer
41 views

Derivation of centripetal acceleration

While reading HC Verma chapter 7 circular motion I came across a derivation which I couldnt understand. I have marked my doubt with red. I don't understand from where +dw/dt [- i sine +j cos0] came ...
0
votes
0answers
22 views

kinematic constraint of spacecraft

I am now reading a paper about trying to use convex optimization to solve the attitude control of spacecraft. However, I do not have background on the physical part: Let 1. $\omega(t) = [\omega_1(...
2
votes
1answer
58 views

Problem on rotation

So this is the problem:A wheel of radius of gyration k is placed on a belt moving with a speed v, which is maintained constant by means of an external agency. Assume that the axis of the wheel is ...
0
votes
1answer
30 views

Why do we represent the axis of rotation using vectorial notation [closed]

When a body (in pure rotation) rotates along an axis passing through it, why do we represent the axis of rotation in vectorial notation? Wouldn't it be sensible enough to represent the angular ...
0
votes
1answer
34 views

instantaneous velocity center

The instant center of rotation, also called the instantaneous velocity center is the point fixed to a body undergoing planar movement that has zero velocity at a particular instant of time. For ...
-1
votes
1answer
57 views

Vertical circular motion(with gravity)

Let's say I have a stone tied to a string and swing it vertically upwards. Now, if I provide an initial velocity such that the velocity of the stone = 0 at an angle greater than 0 from the horizontal(...
0
votes
1answer
32 views

Rotation and Momentum

I understand that according to one of Euler's theorems, any solid object's 3D rotational orientation can be represented by a single 3D vector and an amount, i.e. a 4D vector. However, is it correct ...
1
vote
1answer
84 views

Pendulum question- Angular momentum-impulse

The pendulum of mass m and length l is released from rest at $\theta=0$. Using only the principle of angular impulse and momentum, determine the expression for $\ddot \theta $ in terms of $\theta$, ...
0
votes
1answer
51 views

A vector in a rotating frame. Find the rate of change of this vector ('particular step derivation') [duplicate]

I am doing a project with the fundamental background not in my major. I am reading the following lecture: How to get the green part? Can anyone show me the detailed derivation or provide ...
1
vote
0answers
48 views

Why does a fan blade appear to spin backwards when spun really fast?

This a phenomenon which I notice everyday but never really took an interest in. Why does a fan (or any other rotary object), when spinning really fast, 'appear' to slow down, upto a certain rpm, then ...
1
vote
0answers
45 views

Centripetal acceleration [closed]

I know if a particle is accelerating around the earth it has $$a= \omega*v$$ My question is how do I express this in terms of the unit vector. Would it go something like this. $$|a| = |\omega*v| $$ $...
0
votes
3answers
98 views

Centripetal and Centrifugal force

If water stays in a pail of water that is whirled around a circular path, the water stays in the pail. But is it because of centripetal force or inertia? I'm getting confused by all the different ...
0
votes
2answers
43 views

Momentum of a rack and pinion gear system excited by a time variant force

Background I have a rack and pinion gear system as shown in the image below The pinion gear is attached to a flywheel at the back. The first state of the system, none of the gears or the ...
-2
votes
1answer
31 views

Newton's 2nd law for rotation (accelerated rolling and inertial frame of reference) [duplicate]

I need help in understanding why, in accelerated rolling, the center of mass must be at the origin of an inertial frame of reference in order for the second law to be applicable. Thanks!
0
votes
1answer
48 views

Angular momentum definition? [closed]

The definition of linear momentum is this: Momentum is a vector quantity defined as the product of an object's mass, $m$, and its velocity, $\vec v$. So According to that definition,The definition ...
1
vote
2answers
55 views

When it is usually taken as $\omega=v/r$, why in this particular case $\omega=v/3r$ is taken?

A circular disc of mass m and radius r is set into motion on a horizontal floor with a linear speed v in the forward direction and an angular speed w =v/3r in clockwise direction .Find magnitude of ...
0
votes
1answer
67 views

Friction of a scissor [closed]

How can the friction by a scissor blade be related to its angle? To be more specific this is the question that I came across. A scissor is used to cut a wire of circular cross section and ...
0
votes
1answer
27 views

For a rolling object, is the tangential velocity the same as the velocity of the center of mass?

For example, a solid disk rolling down a hill would include both rotational and linear kinetic energy. For the rotational kinetic energy ($\frac{1}{2}I\omega^2$) the angular velocity becomes $v/r$ but ...
0
votes
2answers
36 views

Why does the angular speed formula end up in radians per second?

So, in my homework I am given the radius and also the tangential speed $v$, the measurement for radius is meters; the measurement for $v$ is $m/s$. I don't understand how by after calculating the RPM ...
2
votes
5answers
64 views

Two identical disks pulled differently question (Kinetic Energy)

I am currently taking a basic physics course in college and I am having a bit of trouble on this problem that deals with rotational and translational kinetic energy. Let's begin: The question: The ...
0
votes
3answers
53 views

Axis of rotation and rotating rigid body [closed]

We know that angular momentum of a solid disk rotating with angular velocity $\omega$ is given by $I\omega$ about its center. Now if I chose any axis (parallel to above), will it have same magnitude ...
1
vote
1answer
43 views

How to find angular velocity of rotated objects in 3D

I am trying to obtain equation for angular velocity of rotated object in 3d. I started with defining yaw, pitch and roll angles. Then I wrote rotation matrices from these angles. As I understand it ...
0
votes
1answer
23 views

Objects rotating and rolling without slipping

The question below confused the hell out of me. It's pretty much straight forward but until the point of where to use which radius. I know that I'll have to use the formula Tr=Iα and then we simplify ...
0
votes
2answers
39 views

Proof derivative of a vector following precession motion

I do not get some points of this proof about the time derivative of a unit vector $\hat{u}$ (costant magnitude) which is following a precession motion. The picture is the following. I want to ...
0
votes
1answer
47 views

Question about friction in rolling without slipping?

I was under the impression that for a ball/cylinder to roll without slip, there must be a static friction force that opposes the direction of motion. Why, in this case, does the friction act in the ...
0
votes
1answer
33 views

Proof of constant angular velocity in rigid body motion

I'm studying rigid body motion on Landau but I'm having troubles to understand this proof of the fact that the angular velocity $\vec{\Omega}$ is constant for a rigid body. My doubt is about the ...
1
vote
1answer
47 views

Why will kinetic energy decrease?

Specific situation : A ring of mass M and radius R is rotating about its axis with angular velocity w. Two identical bodies each of mass m are now gently attached at the two ends of a diameter of the ...
1
vote
3answers
51 views

Why the similarity in the Equations of Motion for Rotational and Rectilinear Motion?

These are the equations of motion given constant acceleration, for first rectilinear and then rotational motion. Rectilinear Motion: Rotational Motion: While the variables have changed, and the ...
0
votes
0answers
58 views

Kinetic energy of rotating rigid body

Sorry for boring you my friends. I am haunted by a problem of kinetic energy of rotating rigid body. Usually, the kinetic energy is calculated in the attached body reference. Because we could take the ...
0
votes
1answer
24 views

Interial Momentium Question

I had a question for my Physics 101 class and was wondering if anyone could share some insights. The question was stated as follows. A pottery wheel of radius 0.5 m and mass 15 kg rotates ...
0
votes
0answers
33 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 ...
0
votes
0answers
31 views

Relation between linear and rotational motion of molecules?

The temperature of a substance, such as an ideal gas, can be related to the root mean square speed of the molecules. For example, for gases the molecules travel at about 480 meters per second. If we ...