j_bertolotti

j_bertolotti, 10 months ago to physics

A little classical mechanics problem you can solve without doing any calculation:
Consider the hyper-simplified problem of a bell-shaped hill, and a point rock that can slide without friction up and down the hill. If you start with the rock at the bottom, and give it exactly the kinetic energy needed to arrive to the top and stop there without sliding on the other side, how long will it take to arrive there?
#Physics #ITeachPhysics

j_bertolotti, 1 month ago to random

#PhysicsFactlet: The "Ashcroft/Mermin Project"
I will try to (likely very slowly) go through the classic textbook "Solid State Physics" by Ashcroft and Mermin and make one or more animation/visualization per chapter.
This will (hopefully) help people digest the topic and/or be useful to lecturers who are teaching about it. As with all my animations, feel free to use them.
The idea is that the animations are a companion to the book, so I will give only very brief explanations here.

j_bertolotti, 2 months ago to random

#PhysicsFactlet
Common misunderstanding about #Entropy: the two configurations below have exactly the same entropy, and in both cases the entropy is zero (as you know exactly where each dot is, so there is only one possible microstate they can be in).

j_bertolotti, 8 months ago to physics

There are many situations in the real world where small initial differences can easily grow into very large differences just out of pure chance.
Since we are on a social network, let's create a toy model* where a number of posts all have the same probability to be reposted/shared/boosted by any person seeing them. Since the more people see a post, the more people have a chance of boosting it, the posts with more visibility are also the ones that are likely to gain more visibility. So small initial fluctuations (just one or two extra boosts at the beginning) can lead a post to skyrocket in popularity, even though it is not intrinsically "better" than any of the other.
If we simulate this process numerically and make a histogram of the result, we see that the distribution of how many boosts a post had rapidly grows a tail, with most posts having no visibility whatsoever, and a few having a LOT more than the average.
#ITeachPhysics #ProbabilityTheory #ToyModel

• In the #Physics jargon, a "toy model" is a very simple (often unrealistic) model, which nevertheless capture the essence of the problem, without being burdened by all the real world complications. If you ever heard about spherical cows in vacuum, that is a toy model!

Animated gif with two plots, side by side. On the left plot a large number of orange dots starts from the bottom, and gradually rise, with a few rising much faster than the other. On the right plot is a histogram of the data showed on the left, that starts as a narrow distribution and then expands into having a long tail.

j_bertolotti, 10 months ago to physics

Haven't seen much discussion on the recent room-temperature superconductivity claims here on Mastodon (am I following the wrong people?), but before the hype hits you, here is the current state of affairs:

• Two experimental attempts to replicate the result have found nothing (https://t.co/D1gmAEOvzx, https://t.co/u5qIEv7aB7)
• One numerical result shows that the suggested material should have flat eletron bands, which are consistent with (but do not prove) superconductivity (https://t.co/2m0ojMOTLr).

Until we have independent experimental replication, any hype is premature.

(h/t @dangaristo)

#Physics

j_bertolotti, 9 months ago to random

Hot take: currency symbols are units, like kg or Hz. And units go AFTER the number, not before!

j_bertolotti, 7 months ago to random

If there is something years of Xwitter has thought me, is to have a VERY low bar for blocking people.
If you have bad vibes from someone, chances are you are better blocking them on sight and continue with your life.

j_bertolotti, 10 months ago to random

The first time I ever heard the word "fortnight" was when somebody told me that one furlong per fortnight is almost exactly 1 cm per minute.
That was also the first time I was exposed to the word "furlong". You can imagine my confusion.

j_bertolotti, 8 months ago to physics

Just made this (as a variation on an old animation) for a talk, so why not show it here?
(hand-coded) finite element simulation of a pulse hitting a disordered medium and being scattered around.
#PhysicsFactlet #ITeachPhysics #Physics #Optics

A number of randomly arranged grey dots show where the scattering centres are. A green pulse of light arrives from the bottom, hits the scatterers, and is dispersed around.

j_bertolotti, 7 months ago to DnD

One of my most controversial opinions is probably that #GURPS is actually easier (and less crunchy) to run than #DnD.
#ttrpg

j_bertolotti, 1 year ago to random

I am a late adopter of new technologies. I try to read about what it is new, but I highly prefer to wait until I am convinced making the jump to a new technology is truly worthwhile.
I was a relatively late adopter of FB, and only jumped in because a ton of my friends were there and it was a convenient way to keep in contact with them when I emigrated.
I was a relatively late adopter of Twitter, and only jumped in because FB had become unbearable, and I had a ton of colleagues active on Twitter, so I immediately had some sort of community there.
Now Twitter is getting worse and worse (but don't make the mistake to think it is dead, it is very much alive. Damn, even FB is still very much alive!) and so I am trying out Mastodon. But the only reason I jumped in is that I knew @ColinTheMathmo from Twitter, and I knew I could trust a server where he was an administrator. But Mastodon is not a Twitter replacement. I am not saying it is better or worse, I am saying it is different. For some people it is different in the "right" way, for some people it isn't. And I am bit tired to see the people for whom Mastodon is different in the "wrong" way being dismissed like they are somehow at fault.

j_bertolotti, 10 months ago to random

Actually, ᵡ is pronounced "Chi".

j_bertolotti, 2 months ago to ubuntu

I assume there is a very good technical reason for #Ubuntu to use #snap, but honestly, after years of getting #Linux more and more approachable by casual users, having to fiddle with the command line every few weeks because the system complains it can't update this or that feels like a huge step back.

j_bertolotti, 6 months ago to random

#PhysicsFactlet
If you sample N points uniformly on the unit sphere, take for each the halfway point to the north pole of the sphere, and then project is on the x-y plane, you obtain N points sampled uniformly on the unit disk.

(A request from @narain )
#Geometry #ComputerGraphicsTheory

Black and white visualization on N points on a sphere moving smoothly to their halfway point to the north pole and then being projected on the x-y plane.

j_bertolotti, 10 months ago to random

Dear #WebComic authors, I am begging you, put a #rss feed to your webcomic. I really want to read them, but without a rss feed you are creating an unnecessary barrier.

j_bertolotti, 9 months ago to physics

#PhysicsFactlet
Does a chaotic system always behave chaotically?
Not really, as many chaotic systems have a subset of possible initial conditions that lead to a quasi-periodic motion.
As an example, below are two sets (black and orange) of 20 double pendula each, all with the same initial energy, and each group starting with very similar initial conditions.
The first group (black) spread out a little bit with time, but nearby initial conditions keeps evolving into nearby dynamics, which is typical of integrable systems.
On the other hand the pendula in the second group (orange) also starts with similar initial condition, but after a short transient evolve each very differently from each other, which is a mark of a chaotic system.
#Physics #Visualization #Chaos

Simulation of two groups of double pendula. On the left 20 black double pendula that evolve staying very similar to each other. On the right 20 orange double pendula, whose dynamic quickly diverge from each other.

j_bertolotti, 9 months ago to random

My son (5y/o) suddenly developed a passion for labyrinths. After drawing a ton of them by hand over the weekend, today I decided to write a small #Mathematica script to automatically generate them 🤓

j_bertolotti, 8 months ago to random

"The Royal Swedish Academy of Sciences has decided to award the 2023 #NobelPrize in Physics to Pierre Agostini, Ferenc Krausz and Anne L’Huillier “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter.” "
https://www.nobelprize.org/prizes/physics/2023/summary/

j_bertolotti, 7 months ago to random

I have added to my personal webpage a brief high school math-level introduction to what tensors are, with the hope to make them a bit less scary to people encountering them for the first time:
https://jacopobertolotti.com/TensorsIntro.html
#ITeachPhysics #ITeachMath #Tensors

j_bertolotti, 10 months ago to random

Learning math if your goal is to learn engineering/ physics/ chemistry/ biology/ etc can be boring.
BUT
Learning math will make learning engineering/ physics/ chemistry/ biology/ etc so much easier that is extremely well worth doing it (even if you are not particularly passionate about it).

j_bertolotti, 8 months ago to random

90% of the time I need to prepare a talk is spent making little animations to show stuff I could probably explain in 1 minute (like the one below, which took way to long to make).
I think I need help 😞
#AcademicChatter

A green cylinder intersecting with a grey plane. The plane rotates back and forth round the vertical axis, so the intersection between the two (highlighted in red) moves continuously from being a circle to being an ellipsis.

j_bertolotti, 8 months ago to random

🤬 🤬 🤬
#BritishAirways overbooked my flight, so now I am on standby, the queue to the "customer service" is neverending, and I have no clue if and when I will manage to travel 🤬

j_bertolotti, 7 months ago to physics

#PhysicsFactlet:
Signals (e.g. light) move at a finite speed, so there is a time lag between when they are emitted and when they are detected. If the source is moving, the detector will "see" the signal that was emitted at a previous time, not the signal that is being emitted right now, and this time lag can change with time in a complicated way.
(Notice that, as the source is always moving slower than the signal, the detector sees the signals in the same order they were emitted.)
#Physics #ITeachPhysics #Electrodynamics #Optics #Relativity

Left panel: a yellow point, representing a source, moving on a thin grey Lissajous curve, and emitting circles at regular time intervals, whose radius grows linearly with time. The colour of the circle changes gradually from red for the first circle to blue for the last one. A white dot just above the Lissajous curve represents a detector. Right panel: a plot of time of emission vs time of detection, with each point appearing when one of the coloured circles hit the detector. The dots form a wavy monotone curve.

j_bertolotti, 3 months ago to physics

#PhysicsFactlet
A quantum simple pendulum.
The pendulum position is spread out, with opacity here being proportional to the probability that the pendulum is at that position at a given time. The average position of the quantum dynamics is the same as the classical pendulum dynamics (Ehrenfest theorem).

Technicalities: I used the Crank-Nicholson method to evolve the system in time. This is a 1D problem, and the only variable I considered was the angle, with the initial state being a Gaussian.

#QuantumMechanics #Physics #ITeachPhysics #Visualization

Schematic drawing of a simple pendulum oscillating, with its quantum version represented as a distribution of pendula with their transparency proportional to the probability to be at a certain position at any given time.

j_bertolotti, 8 months ago to random

After all these years, I am still finding new typos in my PhD thesis 🤦🏻‍♂️
#AcademicLife