# angular-momentum

Yes, sure its fun to see a lady spin around like that, but I had one of my friends ask me - “Where do you even use this mate?”

Here’s one application that I know very well off.

## Spin Stabilization

If you have ever seen a rocket launch, you might know that sometimes the rockets are given a spin while launching. This is known as spin stabilization.

Basically, the rotational inertia of the rotating body will stabilize the rocket against any disturbances and help maintain its intended heading.

The same principle is used in rifling of firearms as well. **

## YoYo DeSpin

Okay, now there is the question how to “De-spin” the rocket:

Well, you do what the lady does: stretch out your arms and you will slow down !

The rocket has weights connected to a cable that stretch out and almost immediately the rocket slows down. This maneuver is known as the YoYo DeSpin. ( Damn good name ! )

All thanks to the conservation of angular momentum !

Have a good one !

* Another method to stabilization : 3-axis stabilization

10

## Why Does The Proton Spin? Physics Holds A Surprising Answer

“With two up quarks – two identical particles – in the ground state, you’d expect that the Pauli exclusion principle would prevent these two identical particles from occupying the same state, and so one would have to be +½ while the other was -½. Therefore, you’d reason, that third quark (the down quark) would give you a total spin of ½. But then the experiments came, and there was quite a surprise at play: when you smashed high-energy particles into the proton, the three quarks inside (up, up, and down) only contributed about 30% to the proton’s spin.”

You might think that the proton, made up of three spin=½ quarks, has a spin of ½ for that exact reason: you can sum three spin=½ particles together to get ½ out. But that oversimplified interpretation ignores the gluons, the sea quarks, the spin-orbit interactions of the component particles. Most importantly, it ignores the experimental data, which shows that the three valence quarks only contribute about 30% of the proton’s spin. Our model of the proton has gotten more sophisticated over time, as advances in experiment and in Lattice QCD calculations have shown that the majority of the proton’s spin comes from the internal gluons, not from the quarks at all. The rest comes from orbital interactions, with the low-momentum gluons requiring a more sophisticated electron-ion collider to experimentally examine.

After decades of mystery, we’re finally closing in on exactly why a proton spins. Find out the surprising physics behind the simple answer!

3

A new study (published in PLOS Biology) investigated how bats make sharp turns in the air, particularly when they have to grab the ceiling. It turns out aerodynamics have very little to do with it - it’s all about inertia. Just as a figure skater clutches his arms to his chest to increase his speed, bats pull in their wings to help them make turns.

You can read all about it (and see more video) in this piece by my friend Nsikan Akpan over at PBS Newshour.

instagram

Mega Tippy-Top: spinning things often have surprising physics. This giant version of the famous flip-over top must be launched with a string pull to give it enough rotational energy to make the flip. It is also placed on a concave mirror to keep it from wandering too far. Friction with the mirror provides a torque that acts on the existing angular momentum of the top to flip it over.

Physics Reasoning part 2

There is no torque because angular momentum is conserved, and angular momentum is conserved because the heading said “Conservation of Angular Momentum.”

On the direction of the cross product of vectors

One of my math professors always told me:

Understand the concept and not the definition

A lot of times I have fallen into this pitfall where I seem to completely understand how to methodically do something without actually comprehending what it means.

And only after several years after I first encountered the notion of cross products did I actually understand what they really meant. When I did, it was purely ecstatic!

## Why on earth is the direction of cross product orthogonal ? Like seriously…

I mean this is one of the burning questions regarding the cross product and yet for some reason, textbooks don’t get to the bottom of this. One way to think about this is :

It is modeling a real life scenario!!

The scenario being :

When you try to twist a screw (clockwise screws being the convention) inside a block in the clockwise direction like so, the nail moves down and vice versa.

i.e When you move from the screw from u to v, then the direction of the cross product denotes the direction the screw will move..

That’s why the direction of the cross product is orthogonal. It’s really that simple!

## Another perspective

Now that you get a physical feel for the direction of the cross product, there is another way of looking at the direction too:

Displacement is a vector. Velocity is a vector. Acceleration is a vector. As you might expect, angular displacement, angular velocity, and angular acceleration are all vectors, too.

But which way do they point ?

Let’s take a rolling tire. The velocity vector of every point in the tire is pointed in every other direction.

BUT every point on a rolling tire has to have the same angular velocity – Magnitude and Direction.

How can we possibly assign a direction to the angular velocity ?

Well, the only way to ensure that the direction of the angular velocity is the same for every point is to make the direction of the angular velocity perpendicular to the plane of the tire.

Problem solved!

3

Superfluid Helium

It was previously thought that superfluid Helium would flow continuously without losing kinetic energy. Mathematicians at Newcastle University demonstrated that this is only the case on a surface completely smooth down to the scale of nanometers; and no surface is that smooth.

When a regular fluid like water is passing over a surface, friction creates a boundary layer that ‘sticks’ to surfaces. Just like a regular fluid, when superfluid Helium passes over a rough surface there is a boundary layer created. However the cause is very different. As superfluid Helium flows past a rough surface, mini tornados are created which tangle up and stick together creating a slow-moving boundary layer between the free-moving fluid and the surface. This lack of viscosity is one of the key features that define what a superfluid is and now we know why it still loses kinetic energy when passing over a rough surface.

Now we can use this information to help our efforts on applications of superfluids in precision measurement devices such as gyroscopes (I think this was on the Big Bang theory where they make a gyroscope using superfluid Helium that can maintain angular momentum indefinitely because it would flow across a smooth surface without losing kinetic energy) and as coolants.

3

Three Experiments Hint at Physics Beyond the Standard Model

The Standard Model of particle physics is a series of mathematical equations used to describe and predict the behaviour of all known particles and forces except gravity. These experiments call into question something known as lepton universality. A lepton is a type of fundamental, half-integer spin particle (spin being intrinsic angular momentum). Half-integer spin fermions are constrained by the Pauli exclusion principle while integer spin Bosons are not (fermions are subatomic particles with a half-integer spin while Bosons are force carrying particles with an integer spin). The Pauli exclusion principle says that two or more identical fermions cannot occupy the same quantum state within a quantum system. For example, if two electrons are on the same orbital with the same principal quantum number, angular momentum and magnetic quantum number values then they must have opposite half-integer spins of ½ and -½.

Lepton universality states that the interactions of these elementary particles are the same regardless of their different masses and lifetimes. The three experiments conducted were measuring the relative ratios of B meson decay. What they found was that the heavy tau lepton has a much higher decay rate when compared to the lighter electrons and muons than the standard model predicts. Together these experiments challenge lepton universality to a level of four standard deviations indicating a 99.95% certainty. However, to be sure that the standard model has to be revised a significance of at least five standard deviations is required.

Changing the Standard Model is no easy feat. Adaptations made to equations anywhere can easily have a knock on effect causing the maths elsewhere to stop making sense. However nothing is certain yet and these results may well be flawed.

2

angular momentum

A set of tops illustrating moments of inertia. Still an idea in evolution with a ways to go, but one of my favorite sculpture ideas I’ve had so far.

A result of my brief obsession with cat physics and angular momentum.

I like to print out PDFs of all my textbooks, comb bind them, and then go on a walk and study them at the same time and bleed all over them with gel pens.

Angular momentum - it makes the world go round!

From I Fucking Love Science on Facebook

10

## Ask Ethan: What’s The Difference Between A Fermion And A Boson?

“Could you explain the difference between fermions and bosons? What differs from an integer spin and a half-integer spin?”

On the surface, it shouldn’t appear to make all that much difference to the Universe whether a particle has a spin in half-integer intervals (±1/2, ±3/2, ±5/2) or in integer intervals (0, ±1, ±2). The former is what defines fermions, while the latter defines bosons. This hardly seems like an important distinction, since intrinsic angular momentum is such a nebulous property to our intuitions, unlike, say, mass or electric charge. Yet this simple, minor difference carries with it two incredible consequences: one for the existence of distinct particles for antimatter and one for the Pauli exclusion principle, that are required for matter as we know it to be. Without these differences, and without these rules, it’s simply a matter of fact that the atoms, molecules and living things we see today wouldn’t be possible to create.

What’s the difference between fermions and bosons? A little difference goes a long way! Find out on this edition of Ask Ethan. (And thanks to the anonymous tumblr question that inspired it!)

Somali Astronomical/Astrological terms

Astronomy/Astrology;
Space = Fagaagga
Space and Time = Fagaagga iyo Semen
Solar System = Iskujoogga qorraxda
The Solar System = Isku-joog qorraxeed
Galaxies = Diillimo-caanoodyo

Planets = Meerayaasha
Planet = Meere
Planet = Malluug

The Sun = Qorraxda
Moon = Dayax
Mercury = Dusaa
Venus = Waxaraxirta(Sugra) ama Bakool
Earth = Dhulka
Mars = Farraare
Jupiter = Cirjeex
Saturn = Raage
Uranus = Uraano
Neptune = Docay

Saturn rings = Garaangaraha Raage ama Saxal
Dwarf planet = meere-cillin ah
Super Nova = Xiddig dhimanaaya

Comets = Dibdheeryo
Meteorider = Burburka jibinta ama xiddigaha ridma
Meteor = Jibin

Open Universe = Koonka Furan
Closed Universe = Koonka Xiran
Expanding Universe = isbaahidda Koonka
Light = ifka
Speed of Light = Xawliga ifka
Cosmos = Koonka
Color Spectrum = shucaaca ilayska-ifka

Astronomy = Xiddiga'aqoonta
Satellite = Dayaxgacmeed
Space Exploration = Sahminta fagaagga sare adduunka
Earth-based observatories = Rugaha kuurgalka fagaagga dhulkaku Saldhigan
Research Centres = Rugo cilmibaaris
Spaceships = Maraakiibta cir-maaxidda
Telescope = Doorbin
Zoom = Waxweyneynta
Observatories = Rugo-kuurgal

Spherical = Ugxan
Rotation = meerwareeg
Rotate = udub-wareeg
North Pole = Qudbiga waqooyi
South Pole = Qudbiga konfur
Northern Lights = Wirwirka Qudbiga woqoyi
Southern Lights = Wirwirka Qudbiga koofureede
Equator = dhulbaraha

Core = Bu’
Inner core = Bu’da gudo-xigeenka
Greenhouse effect = kulaylkaydinta

Astronomical unit = Halbeegga xiddigaha
Diameter = Dhexroorka
Formula = Hab-xisaabeed

Particles = bitaanbitooyin
Anti-Particles = lidka-bitaanbitooyinka
Particles = iniino
Nuclear reaction = iskushubmidda bu'aha
Magnetic Field = Birlabta
Charge electricity = Cabbeynta Shixnadaha Jacda

Circuit: Mareegta
Current= Qulqulka
Forces = Xoogag

Inertia Law = Xogta qaynuunka nuuxsi wax-negaadsan
Acceleration = Xowli
Response Act = Qaynuunka falka iyo falcelinta
Theory of Relativity = Fikriga isudhiganka
Mass = Jir
Energy = Tabarta
Electromagnetic wavelengths = Dhererka hirarka ku danabeysan birlabta

Aries = laxo
Scorpion =daba-alleele ama dib-qallooc
Cancer = naaf
Gemeni = mataanaha
Virgo = afaggaal
Sagittarius = dameerajoogeen
Leo = Libaax

Resistor = Caabiye
Diode = Laba Qotinle
Transformer = Dooriye
Socod Karaarsan = Accelerated Motion
Samaan = Time
Barobax = Displacement
Fogaan = Distance
Karaar = Acceleration
Keynaan = Velocity
Xawaare = Speed
Celcelis = Average
Socod Winiin = Circular Motion
Barobax –xagleed = Angular Displacement
Karaar –xagleed = Angular Acceleration
Keynaan –xagleed = Angular Velocity
Xoog = Force
Culeys = Weight
Xoog –cuf –isjiidad = Gravitational Force
Xoog –dilaac = Shear Force
Xoog –giigsan = Tensile Force (tension)
Xoog –islis = Frictional Force
Xoog –ligan = Normal Force
Xoog –taab = Tangential Force
Xoog –urrur = Compressive Force (compression)
Xoog –xudumeed = Centripetal Force
Weheliyaha isliska = Coefficient of Friction
Gujo = Impulse
Gujo –xagleed = Angular impulse
Kalka = Period
Maroojin = Moment
Maroojinta Wahsiga = Moment of inertia (Angular mass)
Tamar = Energy
Hawl = Work
Awood = Power
Tamar-keyd = Potential Energy
Tamar-socod = Kinetic Energy

Speed = Xawaare
Velocity = Kaynaan
Acceleration = Karaar (I think this is more appropriate than xowli and this is how i remember it from Fiisigiska)
Deceleration = Karaar-jab

Average Velocity： Kaynaan Celcelis
Diffusion: Saydhin
Infrared: Casaan Dhiimeed
Decay: Qudhmis
Decay series: Qudhmis isdaba Joog
Resistance: Iska caabin
Concave Mirror: Bikaaco Golxeed
Convex Mirror: Bikaaco Tuureed
Virtual Image: Humaag Beeneed
Real Image: Humaag runeed
Displace Ment: Baro bixin
Vector: Leeb
Hir = Wave
Daryan = Echo
Itaal = Intensity
Tooxda maqalka = Range of audibility
Danan = Pitch
Isku duba-dhac = Resonance
Ileys = Light
Noqod = Reflection
Daahfurran/gudbiye = Transparent
Falaar abaareed = Incident ray
Golxo = Concave
Tuur = Convex
Xagasha qiirqiirka = Critical angle

Xisaab - Maths

Tiro = Number
Tiro tirsiimo = Natural number
Tiro idil = Whole number
Abyoone = Integer
Jajab/Tiro lakab = Rational number
Mutaxan = Prime
Farac = Composite
Tiro maangal ah = Real number
Tiro maangad ah = Imaginary number
Tiro kakan = Complex number
Faraq = difference
Taran = Product
Qeyb = Quotient
Urur = Set
Hormo-urur = Subset
Hormo-urur quman = Proper subset
Dhextaal = Intersection
Isutag = Union
Duleedin = Complement
Aljebro = Algebra
Doorsoome = Variable
Tibix = Term
Hawraar = Expression
Tibxaale = Polynomial
Heer = Degree
Hawraar lakab = Rational expression
Isirayn = Factorization
Isir = Factor
Isle’eg = Equation
Isle’eg toosan = Linear equation
Sunsun = Sequence
Dareerimo = Series
Faansaar = Function
Wanqar = Symmetry
Tikraar = Intercept
Weydaar = Inverse
Qiime sugan = Absolute value

Joomitiri - Geometry

Bar = Point
Xariiq = Line
Xagal = Angle
Fool = Bearing
Barbaro = Parallel
Qoton = Perpendicular
Sallax = Plane
Goobo = Circle
Dhexroor/Dhexfur = Diameter
Qaanso = Arc
Fatuuq = Sector
Labojibaarane = Square
Dhinac = Side
Laydi = Rectangle
Joog = Length
Balac = Width
Sal = base
Dherer = Height
Gundho = Centroid
Barbaroole = Parallelogram
Koor = Trapezoid
Qardhaas = Rhombus
Gunbur = Pyramid
Toobin = Cone
Dhululubo = Cylinder
Gabal Toobineed = Conic section
Goobo = Circle
Saab = Parabola
Gees = Vertex
Jeedshe = Directrix
Kulmis = Focus
Qabaal = Ellipse
Kulmisyo = Foci
Dhidib weyne = Major axis
Dhidib yare = Minor axis
Labosaab = Hyperbola
Dhidib-xisti = Conjugate axis
Taxaneyaal = Matrices
Taxane = Matrix
Jiiftax = Row
Joogtax = Colunm
Suge = Determinant
Leeb = Vector
Itimaal = Probability
Abnaqan = Factorial
Racayn = Combination
Waqdhac = Event
Xigidda = Differentiation
Xigsin = Derivative
Lid-xigsin = antiderivative
Abyan = Integration
Abyane huban = Definite integral

instagram

Universe Wheel with LEDs: kinetic toy rotor rolls with magnetic connections to rails in the shape of a Möbius strip. A motor in the base rocks the structure keeping the rotor in motion continuously–on each pass the rotor flips and is either on the inside of the tracks or the outside. This toy is a fancy version of the Whee-Lo type toys featured in my previous post with physics of angular momentum, magnets, and rotational/translational kinetic energy.

Hi! Sorry if this is a dumb question, but how is it possible that particles with 1/2 integer spins can only look the same after 2 rotations? I just don't see how it could possibly look the same after 2 but not 1? Maybe I'm thinking of it wrong? AaaahhHhh? Thanks!!

Quantum spin doesn’t actually describe how particles rotate, as weird as it is. Because particles are described as infinitely small points, they can’t “rotate” like a globe. The intrinsic spin of a particle describes its angular momentum and magnetic moment, but the analogy quickly breaks down after that. The reason why particles can only have half-integer of full-integer spins is because this property can only come in discrete amounts, unlike the continuous nature of classical angular momentum. This may not be a very satisfying answer, but such is the nature of quantum mechanics. Thanks for asking!

10

This is an Euler’s Disk. It’s a physics toy that demonstrates angular momentum, potential energy, and kinetic energy.

9

Figure Skating Elements: Upright and Layback Spins

There are four main categories of spins in figure skating: upright spins, layback spins, camel spins, and sit spins. This post will cover upright and layback spins. Upright spins are defined as spins with at least one extended leg on the ice and the body in a more-or-less upright position. Laybacks are scored as a separate element from upright spins; they appear as LSp on protocols while general upright spins appear as USp.

There are many, many, many variations on spin positions in skating; in fact, coming up with interesting positions and combinations is one way to get higher levels on spins. (A common criticism of the judging system is that it encourages weird or ugly spin positions in the name of difficulty and gaining points.) It’s impossible to account for all of the variations out there, so I’ve only gifed some common positions and famous variations.