Standing waves are a common phenomenon usually shown through the vibrations of bridges or springs. Horizontal standing waves are produced in a lab by students shaking cords, springs and bungee cords. However, standing waves can also be produced in a vertical fashion by a single student. Using the new nylon Spring Wave, students are able to produce vertical standing waves easily and calculate the speed of the spring. This is a great little "twist" on the age-old standing wave lab that you have in your arsenal.
Some physical principles have been considered immutable since the time of Isaac Newton: Light always travels in straight lines. No physical object can change its speed unless some outside force acts on it.
Not so fast, says a new generation of physicists: While the underlying physical laws haven’t changed, new ways of “tricking” those laws to permit seemingly impossible actions have begun to appear. For example, work that began in 2007 proved that under special conditions, light could be made to move along a curved trajectory — a finding that is already beginning to find some practical applications.
Now, in a new variation on the methods used to bend light, physicists at MIT and Israel’s Technion have found that subatomic particles can be induced to speed up all by themselves, almost to the speed of light, without the application of any external forces. The same underlying principle could also be used to extend the lifetime of some unstable isotopes, perhaps opening up new avenues of research in basic particle physics.
The findings, based on a theoretical analysis, were published in the journal Nature Physics by MIT postdoc Ido Kaminer and four colleagues at the Technion. The new findings are based on a novel set of solutions for a set of basic quantum-physics principles called the Dirac equations; these describe the relativistic behavior of fundamental particles, such as electrons, in terms of a wave structure. (In quantum mechanics, waves and particles are considered to be two aspects of the same physical phenomena). By manipulating the wave structure, the team found, it should be possible to cause electrons to behave in unusual and counterintuitive ways.
Bouncing neutrons probe dark energy on a table-top, measuring gravity's effects at the quantum scale finds no deviations from Newton's laws.
In this week's Physical Review Letters2, a team led by physicist Hartmut Abele at the Technical University of Vienna shows that the ordinary laws of gravity are still valid even when measured over the scale of a few micrometres. The researchers measured quantized gravitational energy levels with a precision that is 100,000 times better than in previous experiments3.
That precision is sufficient to test some proposed explanations for dark energy — the unknown force that seems to be accelerating the expansion of the Universe. Some models of dark energy put constraints on particular gravity-like forces that would subtly distort the quantum levels at these micrometre scales. “It’s really a beautiful experimental tour de force,” says Geoffrey Greene, a physicist at the University of Tennessee in Knoxville who was not involved in the study.
'Chameleon' dark energy is one such hypothesized force. It derives its name from the way the range over which it acts is reduced drastically for dense objects, which would account for why we fail to see it in Solar System measurements. Such a 'fifth force', existing alongside the known electromagnetic, strong, weak and gravitational forces, would tweak the neutrons' energy levels from those predicted by gravity alone, says Amol Upadhye, a theoretical physicist at Ewha Womans University in Seoul, who was not part of the research team.
The team’s results put a limit on how strong that force could be. “This limit is one hundred times better than the previous such limit,” says Upadhye. This does not eliminate chameleon theories as possible explanations for the dark energy, he adds. “There are still some seven orders of magnitude to cover … but this goes a long way towards closing that gap.”
The results also constrain the properties of a potential candidate for dark matter, the substance thought to make up 85% of matter in the Universe but which seems to be undetectable except for its gravitational pull at cosmic scales. Very light hypothetical particles called axions would cause a deviation from the ordinary law of gravity at short distances. The absence of such an effect in this latest study limits how strong these interactions could be.
"It's truly remarkable that experiments such as this are possible at all," says Upadhye. The researchers call the technique gravity resonance spectroscopy, because it mirrors other kinds of spectroscopy, which measure the energy states of electrons in the electromagnetic field of an atom. These have found a wide range of uses — from determining the composition of faraway galactic objects to atomic clocks. “This first application of the new technology is a big step," says Greene.
"Excellent educational content can be found on YouTube. However, not every teacher can access YouTube in his or her classroom. That's why a few years ago I compiled a big list of alternatives to YouTube. Over the years some of those sites have shut-down, started charging a fee, or have switched into another market. So this evening I went through and eliminated some sites from the list and added a few new ones."
This exploratory’s emphasis is on the introduction of Newton's 1st, 2nd and 3rd laws. At each station students are asked to perform one or more activities and answer questions based on their observations. These stations use a variety of...
In this clip from Mythbusters, the team demonstrates what happens when you fire a ball out of a cannon that is traveling the opposing way, but at the same velocity. If you think about it, it's pretty obvious. But however strong your logic (or even your mathematics and understanding of physics) is, it still doesn’t quite seem right when you see it through a high-speed camera. Next time, we want to see a bullet being fired from a rocket car.
Below are a series of simulated situations used to illustrate major ideas in physics. Next to each link I give you a few things to consider as you explore the environment that was recreated in the program.
If you don't already know why a helium balloon tethered to the floor of a minivan has the power to make your jaw drop, you're going to want to see this. Seriously – set aside five minutes of your time, have a seat and watch. You won't regret it.
American Live Wire Stephen Hawking's black holes 'blunder' stirs debate CBC.ca The U-turn from Hawking, one of the pioneers of modern black hole theory, surprised his colleagues, said Amanda Peet, a theoretical physicist and associate professor at...
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