In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity—the total angular momentum of a closed system remains constant.
In three dimensions, the angular momentum for a point particle is a pseudovector r × p, the cross product of the particle's position vector r (relative to some origin) and its momentum vector; the latter is p = mv in Newtonian mechanics. Unlike momentum, angular momentum depends on where the origin is chosen, since the particle's position is measured from it.
Just as for angular velocity, there are two special types of angular momentum of an object: the spin angular momentum is the angular momentum about the object's centre of mass, while the orbital angular momentum is the angular momentum about a chosen center of rotation. The total angular momentum is the sum of the spin and orbital angular momenta. The orbital angular momentum vector of a point particle is always parallel and directly proportional to its orbital angular velocity vector ω, where the constant of proportionality depends on both the mass of the particle and its distance from origin. The spin angular momentum vector of a rigid body is proportional but not always parallel to the spin angular velocity vector Ω, making the constant of proportionality a second-rank tensor rather than a scalar.
Angular momentum is an extensive quantity; i.e. the total angular momentum of any composite system is the sum of the angular momenta of its constituent parts. For a continuous rigid body or a fluid the total angular momentum is the volume integral of angular momentum density (i.e. angular momentum per unit volume in the limit as volume shrinks to zero) over the entire body.
Torque can be defined as the rate of change of angular momentum, analogous to force. The net external torque on any system is always equal to the total torque on the system; in other words, the sum of all internal torques of any system is always 0 (this is the rotational analogue of Newton's Third Law). Therefore, for a closed system (where there is no net external torque), the total torque on the system must be 0, which means that the total angular momentum of the system is constant. The conservation of angular momentum helps explain many observed phenomena, for example the increase in rotational speed of a spinning figure skater as the skater's arms are contracted, the high rotational rates of neutron stars, the Coriolis effect, and the precession of gyroscopes. In general, conservation limits the possible motion of a system but does not uniquely determine it.
In quantum mechanics, angular momentum (like other quantities) is expressed as an operator, and its one-dimensional projections have quantized eigenvalues. Angular momentum is subject to the Heisenberg uncertainty principle, implying that at any time, only one projection (also called "component") can be measured with definite precision; the other two then remain uncertain. Because of this, the axis of rotation of a quantum particle is undefined. Quantum particles do possess a type of non-orbital angular momentum called "spin", but this angular momentum does not correspond to a spinning motion.
I think angular velocity can be measured in radians/second. I also heard that if I multiply a value of angular velocity that is in the units of Rad./sec. by a certain value of radius in meters, I will get m/s, but this is the instantaneous tangential velocity.
Is any of these right?
In...
Homework Statement
a motor traveling at a constant speed is just able to completely go round a vertical circular track of radius 8m The total mass of motor is 210kg
i)Compute the angular velocity at the top of the track
ii)compute the maximum force on the track
Homework EquationsThe Attempt...
Homework Statement
A small circular block of mass M traveling with a speed v on a frictionless table collides and sticks to the end of a thin rod of with length D and mass M. The picture shows a top down view of the block and rod on the frictionless table. What is the rod's angular velocity...
Homework Statement
A counterweight of mass m 5 4.00 kg is attached to
a light cord that is wound around a pulley.
The pulley is a thin hoop of radius R =
8.00 cm and mass M = 2.00 kg. The spokes have negligible
mass. When the counterweight has a speed v, the pulley
has an angular speed v = v/R...
Homework Statement
A uniform cylinder of mass M and radius R can be rotated about a perpendicular axle through its centre. A particle of mass m is attached to the cylinder's rim. The system is rotated with angular velocity w about the axle, which is held in a fixed direction during the motion...
Assuming R-pairity and thus the creation/destruction of supersymmetric particles happens in pairs,
how is angular momentum conserved when a particle and its supersymmetric partner have different spin by 1/2?
Homework Statement
Consider the Earth as a rigid body with moment of inertia I1, I2 and I3. The Earth is symmetric around the z-axis (I1 = I2). Calculate the angular frequency w using the euler equations
Homework EquationsThe Attempt at a Solution
Hopefully the image is self-explanatory, if not:
A cylinder is rotating around its central axis with angular momentum L1; an angular impulse, ΔL is then added to the cylinder, perpendicularly with respect to L1.
The hypothetical result is: the cylinder has one angular mometum at the end...
Hello! I was looking to find out about an equation that would tell you the maximum angular velocity an electric motor can put out in terms of the geometry of the motor (area of the rotating coil, number of turns, etc), the EMF applied to the coil, magnetic field surrounding the coil, and so on...
Let's start with an arbitrary solid body rotating around a fixed axis of rotation with angular velocity ##\vec \omega## in the ## \hat z## direction. For simplicity, let's say the origin O is on the axis of rotation. Take a look at the picture I sketched in the next post. Tried my best to be...
Hello! This isn't a homework question, and I don't think it is too homework-like, but if I'm mistaken I apologize. My question is if you had a battery, or some source of electrical energy, hooked up to a coil of wire in a constant magnetic field, in such a way that the wire spins around...
< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >
Hey,
So I am not sure if this is in the right section but feel free to move it.
We are conducting an experiment at school at the moment and are having difficulty understanding all the theory...
Say a ring is spining around the z-axis, an angular impulse is then applied to it in the x-axis, what is the resultant motion qualitatively and quantitatively? How can it be calculated?
(You can make up the quantity of z-angular momentum and x-angular impulse)
I am modelling the attitude dynamics of a satellite. The satellite has a reaction wheel in 1 plane to help control the attitude. There is significant debate about the equation for the net angular momentum of the satellite and what inertia tensors should be used regarding parallel axis theorems...
Lets say one gear is rotating with some angular velocity and its angular momentum vector is pointing up.
A second gear (not rotating) is then allowed to mesh with the first. The second gear has the same radius and moment of inertia as the first.
Is not the angular momentum vector of the second...
I've been tutoring for chemistry and someone asked me to clarify the difference of spin angular momentum and orbital angular momentum without math.
I was trying to think of a metaphor, but I wanted to make sure it's a fair one--the spin angular momentum is like Earth rotating on its own axis...
Hi all,
Quick quantum question. I understand the total angular momentum operation \hat{L}^2 \psi _{nlm} = \hbar\ell(\ell + 1) \psi _{nlm} which means the total angular momentum is L = \sqrt{\hbar\ell(\ell + 1)} But how about applying this to an arbitrary superposition of eigenstates such as...
Hoping this is in the right section! The module is nuclear and atomic physics but it crosses over into quantum occasionally.
I've attached an image of the bit I'm trying to work out.
I've got an exam on this topic in just over a week, so sorry if these posts get annoying, I have a feeling I'm...
Homework Statement
Given: Wheel radius is 20 CM, Gear radius is 5 CM, Coefficient of Static Friction is .2, Weight on rear wheel is 50 N.
What is the minimum force that must be applied to the pedal for the wheel to begin accelerating on a level surface?Homework Equations
Net T = I * a
T = R X...
Homework Statement I have a physical pendulum made of a leg which mass is ignored, with a length of 1m, two objects of mass are placed on the bottom and the top of the leg, the first with a mass of m1= m1, and the second with a mass of m2= 3m1, both are L/2 away from the pivot point.
It's...
Homework Statement
In image below
Homework Equations
Fs=-kx
The Attempt at a Solution
In image below
This question might be amateurish
Why does my answer equate to negative angular frequency when the given result is positive?
[/B]
Homework Statement
If the angular frequency of the generator exceeds 1/sqrt(LC), the average energy stored in the inductor is greater than the average energy stored in the capacitor.
True of False?
Can someone explain to me the derivation of this answer?
Homework EquationsThe Attempt at a...
Hello,
I am setting up a model in ANSYS Workbench Mechanical and I would like to insert an certain angular acceleration. How can I do it?
Thanks a lot!
Given :
A (hypothetical) wheel with a m.o.i. of 1 lb*ft^2
Radius of wheel = 1.9099 inches, therefore circumference of wheel = 1 foot
The wheel is at rest, i.e. zero rotation speed.
A torque of 1 ft/lb is applied for 1 second
Is the result a rotation of 1 r.p.s. (60 r.p.m.) ?
thx
Mike
Homework Statement
A 1.0 kg particle is moving at a constant 3.5 m/s along the line y=0.62x +1.4, where x and y are in meters and where the motion is toward the positive x and y directions. Find its angular momentum about the origin2. Attempt at a...
I constructed my code of the Angular Spectrum Method. However, as the distance between the object and the plane of interest increases, the diffraction pattern never disappears; there is still some sort of a diffraction pattern, and I am expecting that it disappears as distance increases.
Here...
Homework Statement
A rod of length l and mass M is suspended from a pivot, as shown The rod is struck midway alongs its length by a wad of putty of mass m moving horizontally at speed v. The putty sticks to the rod. Find an expression for the minimum speed v, that will result in the rod’s...
Homework Statement
In the figure, a 0.400 kg ball is shot directly upward at initial speed 40.4 m/s. What is its angular momentum about P, 6.65 m horizontally from the launch point, when the ball is (a) at maximum height and (b) halfway back to the ground? What is the torque on the ball about P...
Homework Statement
In the figure, block 1 has mass m1 = 450 g, block 2 has mass m2 = 530 g, and the pulley is on a frictionless horizontal axle and has radius R = 5.3 cm. When released from rest, block 2 falls 71 cm in 5.0 s without the cord slipping on the pulley. (a) What is the magnitude of...
I'm building an excel dragstrip model. I already have a working model that incorporates force exerted at the rear tires, force of drag, and force of rolling resistance. Now, I want to take into account the linear force that acts on the front tires that is required to accelerate them. There is...
Homework Statement
Homework Equations
L = mvr
L = Iw
The Attempt at a Solution
I did not attend this lesson due to some reasons. I read it from the book but I could not understand it well. I know the linear momentum well. However, in angular momentum, we have two equations I don't know...
<< Mentors have notified the OP to show their Attempt at a Solution >>
1. Homework Statement
A uniform rod of length L1 = 1.5 m and mass M = 2.8 kg is supported by a hinge at one end and is free to rotate in the vertical plane. The rod is released from rest in the position shown. A particle of...
So my question is when to apply conservation of angular momentum?When there is no external force ,right?But in the case below
A mass m moves in a circle on a smooth horizontal plane with velocity v0 at a radius R0. The mass is attached to a string which passes through a smooth hole in the plane...
OK, so I'm right in the middle of watching Interstellar and I've just seen the part where they have docked with the 'mothership' and they fire up their engines to get it to rotate. This is so they can generate a centrifugal force to simulate gravity.
My question is - first the ship was not...
Homework Statement
A welding robot consists of an arm (thin rod) that can rotate about the origin point O, and a welding tip, which can freely move along the rod, from the outermost point of the arm A all the way to the center point O. The design invokes two electric motors, one to turn the...
Homework Statement
What is the angular inertia of a disk (cylinder) with...
Maximal radius, rmax = 10cm
Thickness, h = 4cm
density, d = 3g/cm3
rotational axis in its centre (like the axis of clock hand in a disk shaped clock)
Please show and explain your procedure in finding the...
Hi,
I've been wondering is there anyway of calculating the angular speed of a ball after there is a collision of it and another mass. For example a baseball bat hitting the ball. I have not looked up on angular momentum, but is angular momentum involved in this? Based on common sense, I think...
The definition of orbital angular momentum, whether for classical mechanics or for quantum mechanical operators, is rxp. Technically, according to this definition, one particle can possesses orbital angular momentum - in this case about the origin.
But I cannot think of any examples, in...
Homework Statement
The problem
Direct imgur link to problem: http://i.imgur.com/QCc0zj6.jpg
Homework Equations
\alpha = \frac{\tau_{net}}{I}
I = \frac{1}{2}MR^2
\tau = rF = rmg
The Attempt at a Solution
I have figured that the moment of inertia of the entire system must be used for...
Homework Statement
A uniform rod of mass 3.15×10−2kg and length 0.380m rotates in a horizontal plane about a fixed axis through its center and perpendicular to the rod. Two small rings, each with mass 0.250kg , are mounted so that they can slide along the rod. They are initially held by catches...
Hello everyone. I'm new here, though I've been using the site for a long time now. Now, I have a question. =)
Suppose I have a vehicle with 3 wheels, one frontal passive wheel, and two wheels with different motors in the back. How will I go about calculating the angular velocity of the car, if...
Homework Statement
The angle of a pendulum is θ(t)=(0.270rad)cos(4.00t+1.00π), where t is in seconds.
Determine the initial angular velocity.
Homework Equations
ω=2πf
The Attempt at a Solution
[/B]
I solved for the frequency, which was 6.37E-1 Hz and subbed it into the formula above and...
Homework Statement
A gyroscope takes 3.8 s to precess 1.0 revolution about a vertical axis. Two minutes later, it takes only 1.9 s to precess 1.0 revolution. No one has touched the gyroscope. Explain
Homework Equations
ω = Δθ/Δt
ω = ωo + at
The Attempt at a Solution
So is the gyroscope...
Homework Statement
Kepler’s 2nd law of planetary motion says that the radius vector drawn from the Sun to any planet sweeps out equal areas in equal time intervals. By considering the small area swept out by the radius vector in time dt, show that \frac{dA}{dt} = \frac{L}{2m} , where L is...
Are the results of the Angular Spectrum Method and the Fourier Transform of a Fresnel Diffraction be different, or the same? Given the same distance between the input and output plane, and the same aperture.
Homework Statement
Solve: A*sin(ωt + Θ) = L*i''(t) + R*i'(t) + (1/C)*i(t). Where: A=2, L = 1, R=4, 1/C = 3 and Θ=45°.
Homework Equations
The system has to be solved by i(t) = ih + ip. I gave the values to A, L, R, 1/C and Θ. I can also give values to ω, but I've come to a doubt when solving...
Hi,
I'd like to know how to calculate parity and total angular momentum of nuclei which have even Z and even N and also Z and N are magic numbers, such as 8O8 or 20Ca20 (the number before the element is Z and the after one is N).
I don't know how to insert LaTeX formulas.
Thank you in andvance