mikerickson:

clearscience:

We talked about frets on a guitar and how when you push the string into the fret board it raises the pitch on the note by changing the length of the standing wave on the string. Another interesting thing you can do is this: after plucking the open string, just lightly touch the string with your finger at the 12th fret. A sound like a bell or flute will result, as you create the second harmonic of the original standing wave.

Here’s what happens: by touching the string lightly while it’s vibrating, you cause it to come to rest at that point you’re touching. This results in another node, as shown above with the second harmonic. Touching the string at the 7th or 5th fret can make the third and fourth harmonics, with higher numbers of nodes.

But if you touch the string someplace that does not result in equal segments between nodes, no harmonic is produced and the string stops. This is simply math. Guitar players can tell you all the spots where harmonics can be produced, even if they don’t care too much about the math and physics behind it. (Some of them care though!)

Fun Fact: If you’re in tune, hitting the 5th fret harmonic on a lower string will produce the same note as the 7th fret harmonic on the next higher string.  The only exception to this is with the G and B strings because they’re not separated by a perfect fourth.  Still, it’s a cool trick that looks impressive to your non-musically-inclined friends.

(via imagineatoms)

abcstarstuff:

Feynman’s double-slit experiment brought to life

The precise methodology of Richard Feynman’s famous double-slit thought-experiment – a cornerstone of quantum mechanics that showed how electrons behave as both a particle and a wave – has been followed in full for the very first time.

Although the particle-wave duality of electrons has been demonstrated in a number of different ways since Feynman popularised the idea in 1965, none of the experiments have managed to fully replicate the methodology set out in Volume 3 of Feynman’s famous Lectures on Physics.

“The technology to do this experiment has been around for about two decades; however, to do a nice data recording of electrons takes some serious effort and has taken us three years,” said lead author of the study Professor Herman Batelaan from the University of Nebraska-Lincoln.

“Previous double-slit experiments have successfully demonstrated the mysterious properties of electrons, but none have done so using Feynman’s methodology, specifically the opening and closing of both slits at will and the ability to detect electrons one at a time.

“Akira Tonomura’s brilliant experiment used a thin, charged wire to split electrons and bring them back together again, instead of two slits in a wall which was proposed by Feynman. To the best of my knowledge, the experiments by Guilio Pozzi were the first to use nano-fabricated slits in a wall; however, the slits were covered up by stuffing them with material so could not be open and closed automatically.”

In their experiments, which have been published today, Thursday 14 March, in the Institute of Physics and German Physical Society’s New Journal of Physics, Batelaan and his team, along with colleagues at the Perimeter Institute of Theoretical Physics, created a modern representation of Feynman’s experiment by directing an electron beam, capable of firing individual electrons, at a wall made of a gold-coated silicon membrane.

The wall had two 62-nm-wide slits in it with a centre-to-centre separation of 272 nm. A 4.5 µm wide and 10 µm tall moveable mask, controlled by a piezoelectric actuator, was placed behind the wall and slid back and forth to cover the slits.

“We’ve created an experiment where both slits can be mechanically opened and closed at will and, most importantly, combined this with the capability of detecting one electron at a time.

“It is our task to turn every stone when it comes to the most fundamental experiments that one can do. We have done exactly that with Feynman’s famous thought-experiment and have been able to illustrate the key feature of quantum mechanics,” continued Batelaan.

Feynman’s double-slit experiment

In Feynman’s double-slit thought-experiment, a specific material is randomly directed at a wall which has two small slits that can be opened and closed at will – some of the material gets blocked and some passes through the slits, depending on which ones are open.

Based on the pattern that is detected beyond the wall on a backstop – which is fitted with a detector – one can discern whether the material coming through behaves as either a wave or particle.

When particles are fired at the wall with both slits open, they are more likely to hit the backstop in one particular area, whereas waves interfere with each other and hit the backstop at a number of different points with differing strength, creating what is known as an interference pattern.

In 1965, Feynman popularised that electrons – historically thought to be particles – would actually produce the pattern of a wave in the double-split experiment.

Unlike sound waves and water waves, Feynman highlighted that when electrons are fired at the wall one at a time, an interference pattern is still produced. He went on to say that this phenomenon “has in it the heart of quantum physics [but] in reality, it contains the only mystery.”

(via science-in-a-jar)

Put all your bad omens aside
— This is what it really means when a planet is in retrograde

You usually hear about a planet being “in retrograde” from astrologers, which might give you the impression that the term is mystical jargon. In fact, it does have an astronomical meaning. That meaning just happens to come from a rather outdated concept, when the Earth was still the center of the solar system. Today, it explains why planets seem to go backwards in the sky.

A long time ago, some astronomer looked at the sky, noticed that one of these moving stars had started moving backwards, and thought, “This can’t be good.” That set the precedent for the astrological concept of retrograde astronomical motion as an omen of bad times for people on Earth.

When people finally understood that Earth and the traveling stars were actually all planets moving around a central sun, things became a bit more clear. The reason they change direction is because our orbits are different. In the case with Earth and Mars, Mars has a longer orbit and so when we overtake the planet we view it on the starry background as if it is moving backwards.

Retrograde Mars (APOD)

Via io9

(via likeaphysicist)

stellar-indulgence:

Multiple Star Orbits

Binary and multiple star systems are very common in our universe. About half of all stars are found in systems containing two or more stars. This page shows the typical orbits for stars in binary, triple and quadruple star systems. These simulations show perfect star systems with stars of equal masses. Real multiple star systems are usually messier with stars of different masses at very different distances.

Binary Star Systems

Shown on the left is a typical binary star system. The two stars follow elliptical orbits around a common center-of-mass. Shown on the right is a special example of a binary star system where the stars follow perfectly circular orbits.

Triple Star Systems 

Shown on the left is a typical triple star system. There are two stars orbiting each other at close range, and a third, more distant, star orbiting around the first two. Shown on the right is a very unusual type of triple star system. The three stars travel in a figure-of-eight trajectory. Computer simulations have shown that this type of orbit can be stable for billions of years. Nobody has yet found a figure-of-eight triple star system (a few astronomers have tried to find one), but it is possible that somewhere in our Galaxy there are stars which follow this orbit.

Quadruple Star Systems   

Shown on the left is one type of quadruple star system. It consists of two pairs of binary stars orbiting about a common center-of-mass. Shown on the right is another type of quadruple star system. There are two very close stars orbiting each other rapidly. They are orbited by a third star as in a triple star system. These three stars are orbited by a distant fourth star.

 

(via atomic-whale)

A Boy And His Atom: The World’s Smallest Movie

“You’re about to see the movie that holds the Guinness World Records™ record for the World’s Smallest Stop-Motion Film (see how it was made at http://youtu.be/xA4QWwaweWA). The ability to move single atoms — the smallest particles of any element in the universe — is crucial to IBM’s research in the field of atomic memory. But even nanophysicists need to have a little fun. In that spirit, IBM researchers used a scanning tunneling microscope to move thousands of carbon monoxide molecules (two atoms stacked on top of each other), all in pursuit of making a movie so small it can be seen only when you magnify it 100 million times. A movie made with atoms. Learn more about atomic memory, data storage and big data at http://www.ibm.com/madewithatoms”

prussiahasinvaded:

Walter Lewin is a Dutch astrophysicist and professor emeritus of physics at the Massachusetts Institute of Technology (MIT). 

He has taught physics to millions of students through his popular online lectures, always incorporating visual experiments into his lectures to both explain the material and keep the students engaged. 

(via greatmindsofscience)

skeptv:

Jetpack Rocket Science

Jetpacking was awesome fun! Despite the fat lip I had a great time. I think knowing a bit about physics actually helps fly the jetpack. It works on the same principle as a rocket (Newton’s 3rd law) but unlike the shuttle, you don’t carry your own propellant with you. Instead, water is pumped out of the lake by the jetski at up to 60 litres a second. It is then fired out of the nozzles at around 15 m/s creating 1800 N of force, the equivalent of about 150 fire extinguishers. On me this can produce acceleration of about 1.5g’s.

via Veritasium.

thatscienceguy:

The Sonic Boom, as seen above, is caused by the Doppler Effect - that thing Sheldon explained on the Big Bang Theory.

When an object is stationary, while emitting sound, the sound waves spread out uniformly in a circle from the source, as seen in the second image, however when that object begins, as seen in the third image, to move the circles are not emanating from the same position, so the troughs and crests (represented by the black lines) of each wave are in are closer together on one side and further apart on the other.

So when the object is traveling at the speed of sound all the troughs/crests are perfectly aligned on one side, where they then amplify each other (positive and negative superposition) producing a loud burst of sound and also pressurising the air close to the source which is why a cloud is seen.

This effect can also be observed with light, theoritically, however first we need to make something that can, somehow, reach the speed of light ;)

(via physicistsneedlovetoo)

fuckyeahfluiddynamics:

Wine drinkers may be familiar with the “tears of wine” often seen on the wall’s of a glass. The effect is a combination of evaporation and surface tension. As the low-surface-tension alcohol evaporates from the wine film left by swirling the glass, the higher local surface tension draws wine up the walls of the glass. Eventually enough wine gathers that droplets form and slide back down. This timelapse video shows how the beads form and move, almost dancing around the glass. The video’s author, Dan Quinn, has a second video with an awesome visual explanation of the behavior that’s well worth watching, too! (Video credit and submission: D. Quinn)

(Source: liod, via physicistsneedlovetoo)