How Classical Kinetic Energy Is Actually A Subset Of Relativistic Kinetic Energy

Many people think that Classical Physics and Relativistic Physics are two different things. Of course, anyone who has studied both can tell you that one can derive many of the classical physics equations from relativistic equations, proving that classical equations are actually special cases of the more general relativistic equations.

In this Don Lincoln's video, he shows how classical kinetic energy that many students learn in General Physics courses can actually be derived from the more general relativistic energy equation, and why we still use the classical physics equation in most cases.

Z.

Newton's Gravitational Law Still Valid At Sub-Nanometer Scale

A new experiment using neutron scattering off noble gasses has shown no deviation from Newton's gravitational law at 0.1 nm scale.

The team fired pulses of neutrons at a chamber filled with either helium or xenon gas and monitored both the travel time of the neutrons through the gas and the neutrons’ scattering angles. From these measurements, they reconstructed the scattering process with the aid of simulations. They found that the scattering-angle distribution fit the predictions—based only on known laws of physics—for neutrons bouncing off gas nuclei. This result indicates that, within the sensitivity of the experiment, no unexplained force—be it modified gravity or another type of interaction—acts on length scales below 0.1 nm.

This one may not be as transparent, since it required quite a bit of reconstruction to simulate the interaction. So while the length scale being probed has improved considerably, I'm not so sure on how convincing this result is.

Still, where are those curled-up extra dimensions anyway?

Zz.

How Long Can You Balance A Pencil

Minute Physics took up a topic that I had discussed previously. It is about the time scale on how long a pencil can be balanced on its tip.



Note that in a previous post, I had pointed out several papers that debunked the fallacy of using quantum mechanics and the HUP to arrive at such time scale. So it seems that this particular topic, like many others, keeps coming back every so often.

Zz.

Helium Balloon In An Accelerating Vehicle

A while back, in a Part 6 of my Revamping Intro Physics Lab series, I mentioned an "experiment" that students can do involving a suspended helium balloon in an accelerating vehicle. I mentioned that this would be an excellent example of something where the students get to guess what would happen, and at first, what actually happens does not make sense.

Well now, we have a clear demonstration of this effect on video.



There is a good explanation of why this occurs in the video. It is also nice that he included a hanging pendulum in the beginning for comparison, and that this is what most of us are expecting to occur.

Might be a nice one to quiz your kids if you are teaching basic, intro physics.

Zz.

Immovable Object vs. Unstoppable Force

As stated in the video, I too have seen such a question being asked on the internet numerous times. And as can be seen in the video also, question like this is often asked without clearly think of what the question actually means. This is important in physics because the question that we ask can sometime be as important as the answer that we get. So having a clearly defined question is crucial.



Zz.

To Run, Or Not To Run, In The Rain...

... that is the question. And it seems that this question continues to prop up every now and then.

The latest chapter in trying to figure out what to do if one is caught in the rain is a new paper out in Eur. J. of Phys.[1]

Basically, the best strategy for staying dry (or at least somewhat dry) is to run as fast as possible. Unless you’re really thin, in which case there may be a more optimal speed. And if you’ve got a tailwind behind you, then you should run exactly as fast as the wind at your back.

So the answer is, it depends! It depends on the body shape, the wind direction, etc... etc. There isn't one single answer that's applicable to all situations, which to me, makes sense.

So there! Who cares about those damn Higgs bosons? We need to find out how not to get wet in the rain! :)

Zz.

[1] F. Bocci Eur. J. Phys. v33, p.1321 (2012)

Light Shows Non-Classical Properties, But I Don't Get It

OK, this is where you can help me understand this paper in the context of the press report.

This is the paper:

E. Kot et al., "Breakdown of the Classical Description of a Local System", Phys. Rev. Lett., v.08, p.233601 (2012).

Abstract: We provide a straightforward demonstration of a fundamental difference between classical and quantum mechanics for a single local system: namely, the absence of a joint probability distribution of the position x and momentum p. Elaborating on a recently reported criterion by Bednorz and Belzig [ Phys. Rev. A 83 052113 (2011)] we derive a simple criterion that must be fulfilled for any joint probability distribution in classical physics. We demonstrate the violation of this criterion using the homodyne measurement of a single photon state, thus proving a straightforward signature of the breakdown of a classical description of the underlying state. Most importantly, the criterion used does not rely on quantum mechanics and can thus be used to demonstrate nonclassicality of systems not immediately apparent to exhibit quantum behavior. The criterion is directly applicable to any system described by the continuous canonical variables x and p, such as a mechanical or an electrical oscillator and a collective spin of a large ensemble.

From a quick reading of the paper, they are trying to show this:

Classically, the phase space distribution Wðxi; piÞ is the joint probability of finding the system in an infinitesimal area around x = x_i, p = p_i, and hence it obeys all the requirements of a probability distribution including being a non-negative function. As mentioned, in the case of a quantum phase space formulation, introduced by Wigner [9], the Heisenberg uncertainty renders this definition meaningless, as a joint probability distribution for x and p does not exist. The phase space distribution is only defined through the single coordinate (marginal) distributions, projected from the distribution function [10] and this relaxation of constraints allows for negative values of the function in areas smaller than hbar. This negativity is not directly observable due to the vacuum fluctuations preventing simultaneous measurement of x and p. However, one can still infer the phase space distribution from measurements of only a single observable at a time and detect such negativities, thereby illuminating the failure of classical theory.

I think they showed this in Fig. 2.

Fine. However, here's the press release of this work. The lead author was interviewed, and said this:

Based on a series of experiments in the quantum optics laboratories, they examined the state of light. In classical physics, light possesses both an electric and a magnetic field.

“What our study demonstrated was that light can have both an electric and a magnetic field, but not at the same time. We thus provide a simple proof that an experiment breaks the classical principles. That is to say, we showed light possesses quantum properties, and we can expand this to other systems as well” says Eran Kot.

Electric and magnetic field? Not at the same time? What did I miss? The press release doesn't seem to have any resemblance (at least in terms of the experiment and what is being measured) with the actual paper. Can someone clarify this for me?

Zz.

More On Driving And Saving Fuel

So I was driving along the US Interstate over the weekend, and stopped at a rest area on an Illinois interstate (we call them Oasis over here) highway. In the washroom, they have these posters placed in several places, and one of the posters has these things that tells you some "green" driving tips. One of the tips given was something that I had brought up quite a while back. It is on driving with your windows down.

The poster here said this:

Try using vents and opening windows to cool off before you turn on the air conditioner. Air conditioning increases fuel consumption.

Now, if you've read my earlier post when I asked about this, you will also have read the two comments left behind, including one on an investigation done by the Mythbusters folks. Here, it turns out that if one is driving faster than 50 mph, then rolling up the windows and turning on the air-conditioning uses LESS fuel than driving with the windows down and no air-conditioning. The drag forces above that speed causes more use of energy than the air-conditioning unit.

So this poster is not quite up-to-date on "green driving".

Zz.

The Physics of Floating Pyramids

Or as the title of this article goes, it is the UNUSUAL Physics of Floating Pyramids.

It turns out that, based on the research being reported in the article, a top-heavy pyramid appears to be better at straightening itself out when it is floating on a stream of air from below.

The researchers placed hollow paper pyramids inside the cylinder. The objects were about 1 to 5 centimeters high and were made of tissue paper or letter paper on carbon fiber supports, like tiny homemade kites. Physicist Bin Liu led the experiments, attaching a beadlike weight to a post running down the center of the pyramid and changing the height of the bead to give the object a different center of mass. Common sense says that the pyramid should be most stable when the bead is at the bottom of the post, like ballast in the hold of a ship. But when the team released the pyramids over the subwoofer, the opposite was true: The bottom-heavy pyramids were likely to flip over and fall, whereas the top-heavy ones remained upright and continued to hover (see first video), the group reports in an upcoming issue of Physical Review Letters.

The video is available in that link. I'll keep an eye out on PRL and update this entry when I have
the exact citation for the paper.

Zz.

Edit: We have a synopsis of this work AND the exact reference to it.

Sports Versus Physics

Here's a video on a lot of issues related to sports, and the physics involved. The description says that this is from a 2004 lecture. Still, it actually is quite fascinating, if you have roughly 45 minutes to spare.



Zz.

The Physics of Tibetan Singing Bowl

I've seen this on TV before in a documentary show, but I don't think I've been intrigue by it till now.

This is a video of the so-called Tebetan singing bowl:



And he's a paper describing the physics of it:

The Tibetan singing bowl : an acoustics and fluid dynamics investigation

Abstract: We present the results of an experimental investigation of the acoustics and fluid dynamics of Tibetan singing bowls. Their acoustic behavior is rationalized in terms of the related dynamics of standing bells and wine glasses. Striking or rubbing a fluid-filled bowl excites wall vibrations, and concomitant waves at the fluid surface. Acoustic excitation of the bowl's natural vibrational modes allows for a controlled study in which the evolution of the surface waves with increasing forcing amplitude is detailed. Particular attention is given to rationalizing the observed criteria for the onset of edge-induced Faraday waves and droplet generation via surface fracture. Our study indicates that drops may be levitated on the fluid surface, induced to bounce on or skip across the vibrating fluid surface.

Zz.

Tossing A Leaky Bottle

I mentioned previously the column "What Happens Next" in the issue of Physics Education journal. I am a fan of that column because I love thinking about these "mundane" problems or puzzles. We dealt with bouncing grapes in sodas last time.

This time, it is another good one from the May 2011 issue. You have a regular plastic water bottle, filled with water. You poke a hole close to the bottom of the bottle, and another hole close to the top. With both holes opened, the water will flow out of the bottom hole. You can stop that by closing the hole on top. See picture

















But what will happen if you toss the bottle of water up into the air?

I'll post the answer later, because I'm sure you might want to try this out yourself! :)

Zz.

The Physics of Sailing for Pirates

Now, we're not talking about the nasty pirates off the coast of Somalia that have been hijacking ships. We are talking about the romanticized version of pirates here, and since this weekend is the opening weekend of Disney's "Pirates of the Caribbean - On Stranger Tides", this is a good time to talk one aspect of the physics of sailing.

The fastest way to sail is at a forty-five degree angle to incoming wind. I know! Ye minds have been blown! But it works. the best way to understand is to think of the wing of an airplane. It has a flat side an a rounded side. The rounded side is tough for air to get around - it has to move quicker, and there's less of it making the dash - so the air pressure is lower on that side of the wing. The flat side is easy for air to move by, and so the air pressure is higher. That pushes the plane upwards. When wind hits the sail, it puffs out, making one side rounded like an airplane's upper wing, and the other side a hollow. The air pressure in the hollow is high and in on the puff is low. The keel keeps the boat from drifting sideways, and so it moves the only way it can - forward.

So the expression "may the wind be at your back" may not be such a good thing in sailing.

Zz.

Bouncing Grapes In Soda

Again, as I had mentioned before, I love these kinds of "mundane" experiments and finding the physics behind it.

In the March 2011 issue of Physics Education journal, the section on "What Happens Next?" dealt with a very common phenomenon that a lot of people have seen, most of them while sitting at a bar drinking beers. This time, the scenario uses grapes.

You have a glass of a carbonated drink. You drop an unpeeled grape into it. What happens next? Interestingly enough, similar to dropping raisins and peanuts into such carbonated drinks (or beer), the grape will start to sink, and then after some time, it will float back to the surface. This gets repeated over and over again.

But but happens if you drop a peeled grape? Will it act any differently?

And what is the explanation behind all this?

Just so I won't spoil the fun for those who want to offer their explanations, I won't post what the article in the journal has written (you can, of course, "cheat" and look it up yourself). I will make another follow-up post at a later date and reveal to you the explanation.

Zz.

The Musical Turkey Baster

Another physics in the kitchen, and this time, you get instructions on how to turn your turkey baster into a musical instrument. Hey, after all, here in the US, Thanksgiving is barely a month away.

Inside the tube of the turkey baster is a column, or chamber of air. When you blow over the edge of the turkey baster, its edge vibrates, compressing the air inside the tube at equal intervals. The compressed air moves down the column and bounces back toward the opening once it hits the water. By doing this, you have created a standing wave, a wave that remains at a constant position. When you change the water level, it changes the wavelength of the standing wave.

So you get to learn about sound in a standing wave with stuff you find around your house.

Zz.

The Physics of Weight Loss

I thought I'd post a link to this article about simple, basic, physics on weight loss. Although one can quibble a bit about 'arguing with Newton', I would say that nothing in here is surprising as far as the physics is concerned.

And we are all governed by the prevailing laws of physics that relate matter and energy. Calories are a measure of energy, and matter cannot be created without energy input. Arguments against the fundamental role of energy balance in weight regulation -- against calories in versus calories out -- are arguments with Isaac Newton. Folks, nobody wins an argument with Isaac Newton!
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There are, once we are done growing up, three ways we burn calories: physical activity, the generation of heat and just existing. There are technical terms for the second and third: thermogenesis, and resting energy expenditure (sometimes referred to as basal metabolic rate). What should be noteworthy right away is that you are not in charge of two out of the three!

You can choose how much exercise to do. But you don't get to choose how thermogenic you tend to be, and that can matter quite a lot. Like exercise, thermogenesis accounts for roughly 15 percent of total energy expenditure on average, but there is lots of variation on the theme of average. People who generate more heat from calories have fewer available with which to make fat. They tend to be people who can eat a bit more, and stay thin anyway.

 There ya go! That's your health info for the day! :)

Zz.

Mean Free Path In Soccer And Gasses

An interesting title on a familiar topic. This paper presents an intro to students on the concept of kinetic theory of ideal gas, and explains the concept of mean free path in gasses using an analogous approach to the "mean free path" of a soccer ball during a soccer match.

J. Luzuriaga, Eur. J. Phys. v.31, p.1071 (2010).

Abstract:

The trajectories of the molecules in an ideal gas and of the ball in a soccer game are compared. The great difference between these motions and some similarities are discussed. This example could be suitable for discussing many concepts in kinetic theory in a way that can be pictured by students for getting a more intuitive understanding. It could be suitable for an introductory course in vacuum techniques or undergraduate courses in kinetic theory of gases. Without going into the slightly harder quantitative results, the analysis presented might be used for introducing some ideas of kinetic theory qualitatively to high school students.

Published 21 July 2010

Note that you could get a free copy of the paper within 30 days of online publication.

Zz.

London Science Museum's "Launchball"

Hey, this is not a bad game at all!

The London Science Museum launched (pun intended) a Flash-based webgame called "Launchball". It became popular enough that there is now an app for the iPhone.

Launchball is a physics puzzler where you need to get a ball from Point A to Point B using the tools at hand. These tools include fans, magnets, tesla coils, bunsen burners and much more. Each tool is introduced in sequential fashion during the introductory levels and in general feels much more accessible than similar games we've played. Once you set up the board as you want, you can press "start" to set the scene in motion to see if you've succeeded.

You can find the Flash-based web version of the game here.

Zz.

'Overwhelming' Evidence for Monopoles?

A flurry of papers being published and appearing on Arxiv seem to claim the discovery of monopoles {link available for free only for a limited time}, but it is not where you think.

"People have been looking for monopoles in cosmic rays and particle accelerators — even Moon rocks," says Jonathan Morris, a researcher at the Helmholtz Centre for Materials and Energy in Berlin.

Now Morris and others have found the strongest evidence yet for magnetic monopoles, in small crystals about the size of an ear plug. When the crystals are chilled to near absolute zero, they seem to fill with tiny single points of north and south. The points are less than a nanometre apart, and cannot be measured directly. Nevertheless, Morris and other physicists believe they are there. They make their case in two papers published today in the journal Science, and other work published on the pre-print server arXiv.org.

Here are the references:

1. Kadowaki, H. et al. preprint at http://arXiv.org/abs/0908.3568v2 (2009).
2. Fennell, T. et al. Science advance online publication doi:10.1126/science.1177582 (2009).
3. Kadowaki, H. et al. preprint at http://arXiv.org/abs/0908.3568v2 (2009).
4. Bramwell, S. T. et al. preprint at http://arxiv.org/abs/0907.0956 (2009).

It remains to be seen whether these monopoles from the "spin ice" system can actually be considered as the actual monopoles that we've been looking for (don't think this is what the Standard Model had in mind).

Not surprisingly, such a fundamental discovery came, not from cosmic rays or particle accelerators, but from condensed matter physics! There should be no more question on whether CMP studies "fundamental" ideas or not. It should be patently clear already by now.

Edit: adding the link from ScienceNOW on the same topic.

Edit 10/15/09: S.T. Bramwell paper has now appeared in Nature. The exact reference is: S.T. Bramwell et al., Nature v.461, p.956 (2009).

Zz.

The Surprising Physics of Pipe Organs

I love reading stuff like this. For some odd reason, finding the answer to long-standing "common" puzzle has always been something I have always been keen on reading. So when I came around this article, I gobbled it up! :)

The problem deals with a puzzle that was observed by Lord Rayleigh, so it is OLD! It deals with a peculiar behavior exhibited by pipe organs.

In 1877, English physicist Lord Rayleigh observed that when two almost identical organ pipes are played side by side, something strange happens. Rather than each blaring their own tone, the two pipes will barely make a whisper. But put a barrier between them, and they sing loud and clear.

You have to read the whole article to figure out the explanation for this. Fascinating!

Zz.