wave physics

sekkiera  asked:

So, our physics teacher has the strange idea of motivating his students by letting each of us present a physical phenomenal we find interesting to our classmates in a 5-minutes-presentation. And now I need something that is interesting for everyone - even people that usually don't care for physics -, but has interesting facts for someone who's interested in it, too (preferably with an easy experiment). You don't happen to have any ideas, do you?

First of all, your professor is awesome for taking the time to do this. Of the top of my mind, the best one I have is Chladni figures.

Basically take a flat metal plate, fix it at the center and spray some fine sand particles on it.

Using a violin bow, gently excite any edge of the plate to magically witness these beautiful normal mode patterns ( known as Chladni patterns/figures ) forming on the plate.

Also notice that by pinching the plate at different points, the pattern obtained changes.

There is a whole lot of physics that goes behind such a simple phenomenon and I dare say we understand it completely. There are lots of questions on these figures that we have no answer for!

Hope this helps with your presentation. Have a good one!

Gif source video: Steve Mould


Water stuck in a bus window


A human brain has around 86 billion neurons, and the communication between these neurons are constant. The sheer scale of these interactions mean a computer (an EEG) can register this electrical activity, with different frequencies indicating different mental states.


In slow motion, vortex rings can be truly stunning. This video shows two bubble rings underwater as they interact with one another. Upon approach, the two low-pressure vortex cores link up in what’s known as vortex reconnection. Note how the vortex rings split and reconnect in two places – not one. According to Helmholtz’s second theorem a vortex cannot end in a fluid–it must form a closed path (or end at a boundary); that’s why both sides come apart and together this way. After reconnection, waves ripple back and forth along the distorted vortex ring; these are known as Kelvin waves. Some of those perturbations bring two sides of the enlarged vortex ring too close to one another, causing a second vortex reconnection, which pinches off a smaller vortex ring. (Image source: A. Lawrence; submitted by Kam-Yung Soh)

Note: As with many viral images, locating a true source for this video is difficult. So far the closest to an original source I’ve found is the Instagram post linked above. If you know the original source, please let me know so that I can update the credit accordingly. Thanks!

There are over 7 billion brains transmitting and receiving information on this beautiful planet, imagine if we shared the same flow state of love what a different world this would be.


Quantum Double Slit Experiment

The double slit experiment is one of the most well known in modern physics. It supports wave-particle duality, which is a concept in quantum mechanics that every particle is also described partly in terms of waves.

So if a wave passes through a parallel double slit, whether it’s water, sound or light, an interference pattern will be observed. A modified version of the double slit experiment is set up to fire a single photon through a double slit such that the scientists don’t know which slit it travelled through. When the effect against the backdrop is measured, an interference pattern can be observed suggesting the photon travelled through both slits as a wave. However, as soon as they place a detector to determine which slit the photon travels through, the interference pattern disappears, and a splatter pattern can be seen against the backdrop. This shows that the photon travelled through one of the slits as a particle, and not as a waveform. So somehow by the act of observing a particle, we change it.

A modified version of the double slit experiment called the delayed choice experiment, has results that just beg more questions. At each slit they place a crystal which splits incoming photons into identical pairs. One photon from this pair will form a standard interference interference pattern and the other one will travel to a detector. Even if the photon that hits the detector is measured after the first photon hits the screen, it still changes whether or not an interference pattern was observed. So not only can we influence particles just by observing them, but those observations can alter what happened in the past.

This experiment has been repeated with molecules as large as Buckminsterfullerenes (60 carbon atoms) with the same results, and there are plans to attempt the same experiment with viruses.


In their newest video, the Slow Mo Guys recreated one of my favorite effects: vibration-driven droplet ejection. For this, they use a Chinese spouting bowl, which has handles that the player rubs after partially filling the bowl with water. By rubbing, a user excites a vibrational mode in the bowl. Watch the GIFs above and you can actually see the bowl deforming steadily back and forth. This is the fundamental mode, and it’s the same kind of vibration you’d get from, say, ringing a bell. 

Without a high-speed camera, the bowl’s vibration is pretty hard to see, but it’s readily apparent from the water’s behavior in the bowl. In the video, Gav and Dan comment that the ripples (actually Faraday waves) on the water always start from the same four spots. That’s a direct result of the bowl’s movement; we see the waves starting from the points where the bowl is moving the most, the antinodes. In theory, at least, you could see different generation points if you manage to excite one of the bowl’s higher harmonics. The best part, of course, is that, once the vibration has reached a high enough amplitude, the droplets spontaneously start jumping from the water surface! (Video and image credits: The Slow Mo Guys; submitted by effyeah-artandfilm)

The simple harmonic oscillator

Anonymous asked: Please explain the intuition of solving the SHM equation.

Okay Anon! Here you go, this is my rendition.

The problem

You have a mass suspended on a spring. We want to know where the mass will be at any instant of time.

Describe the motion of the mass

The physical solution

Now before we get on to the math, let us first visualize the motion by attaching a spray paint bottle as the mass.

Oh, wait that seems like a function that we are familiar with - The sinusoid.

Without even having to write down a single equation, we have found out the solution to our problem. The motion that is traced  by the mass is a sinusoid.

But what do I mean by a sinusoid ?

If you took the plotted paper and tried to create that function with the help of sum of polynomials i.e x, x2, x3 … Now you this what it would like :

By taking an infinite of these polynomial sums you get the function Since this series of polynomial occurs a lot, its given the name - sine.

I hope this shed some light on the intuition of the SHM equation. Have fun!

You are made from pieces.
Every day they begin their dance through your veins, through your neurons, through the breath you take oven in over to keep you alive. For one particular reason.
If you stop - they stop. If you keep going - they go, keeping you alive for a purpose.
You are motion. Be sure to keep it flow.

How do we know light is a wave?

Before I answer this question, I’ll need to briefly go over a wave property called superposition. Basically, superposition is the idea that two waves can be in the same position at the same time, and interfere with each other:

When the two waves add to each other and make a larger wave, we call this constructive interference. When the waves cancel each other out, we call this destructive interference. 

Now we’re going to move on to the Double Slit Experiment. Basically, you shine a beam of light at a piece of metal, cardboard, etc with two slits in it, with a surface behind it where you can see the light hit it. 

If light is a wave, what we’d expect to see would be an interference pattern created by the light from the first slit interfering with light from the second slit, which is exactly what we see. It’s a pattern of constructive interference (brighter regions) and destructive interference (darker regions), looking like this:

These images are helpful:

that is how we know light acts as a wave!! Click HERE for my post on the particle nature of light.


Gravitational Waves Win 2017 Nobel Prize In Physics, The Ultimate Fusion Of Theory And Experiment

“The 2017 Nobel Prize in Physics may have gone to three individuals who made an outstanding contribution to the scientific enterprise, but it’s a story about so much more than that. It’s about all the men and women over more than 100 years who’ve contributed, theoretically and experimentally and observationally, to our understanding of the precise workings of the Universe. Science is much more than a method; it’s the accumulated knowledge of the entire human enterprise, gathered and synthesized together for the betterment of everyone. While the most prestigious award has now gone to gravitational waves, the science of this phenomenon is only in its earliest stages. The best is yet to come.”

It’s official at long last: the 2017 Nobel Prize in Physics has been awarded to three individuals most responsible for the development and eventual direct detection of gravitational waves. Congratulations to Rainer Weiss, Kip Thorne, and Barry Barish, whose respective contributions to the experimental setup of gravitational wave detectors, theoretical predictions about which astrophysical events produce which signals, and the design-and-building of the modern LIGO interferometers helped make it all possible. The story of directly detecting gravitational waves is so much more, however, than the story of just these three individuals, or even than the story of their collaborators. Instead, it’s the ultimate culmination of a century of theoretical, experimental, and instrumentational work, dating back to Einstein himself. It’s a story that includes physics titans Howard Robertson, Richard Feynman, and Joseph Weber. It includes Russell Hulse and Joseph Taylor, who won a Nobel decades earlier for the indirect detection of gravitational waves. And it’s the story of over 1,000 men and women who contributed to LIGO and VIRGO, bringing us into the era of gravitational wave astronomy.

The 2017 Nobel Prize in Physics may only go to three individuals, but it’s the ultimate fusion of theory and experiment. And yes, the best is yet to come! 


There is sound in space, thanks to gravitational waves

“These waves are maddeningly weak, and their effects on the objects in spacetime are stupendously tiny. But if you know how to listen for them — just as the components of a radio know how to listen for those long-frequency light waves — you can detect these signals and hear them just as you’d hear any other sound. With an amplitude and a frequency, they’re no different from any other wave.”

You’ve likely heard that there’s no sound in space; that sound needs a medium to travel through, and in the vacuum of space, there is none. That’s true… up to a point. If you were only a few light years away from a star, stellar remnant, black hole, or even a supernova, you’d have no way to hear, feel, or otherwise directly measure the pressure waves from those objects. But they emit another kind of wave that can be interpreted as sounds, if you listen correctly: gravitational waves. These waves are so powerful, that in the very first event we ever detected, the black hole-black hole merger we saw outshone, in terms of energy, all of the stars in the observable Universe combined. There really is sound in space, as long as you know how to listen for it properly.

Come learn about it, and catch a live event, live-blogged by me, this evening!


Christopher Walken and The Brain discuss physics  

I stumbled upon this snippet from ‘Pinky and the Brain‘  while researching about Fermi-dirac distributions and still can’t believe this is a cartoon for kids!