Nitinol (NiTi), aka memory wire. It has a phase transition in which the structure changes, and it “remembers” what its shape was.
Category Archives: Experiments
Don't Fence Me In
… or I’ll exhibit quantum behavior.
Objects exhibit quantum behavior when squeezed into a tight space. A new experiment has clearly demonstrated the wave-like properties of a hydrogen molecule inside a tiny carbon cage. Using neutrons to probe the state of the molecular prisoner, the researchers showed quantized states in both rotation and linear motion of the molecule, much like the “ladder” of excited electron states in an atom.
This is Rocket Science!
While I was on vacation I had seen a couple of videos/links about a guy who launched himself with some water rocket of the large soda-bottle variety, and thought that this was the sort of thing Rhett would analyze over at Dot Physics, and as I catch up with my blog reading, I see that it is so: Water Bottle Rocket Guy
“Water bottle rocket guy” is too impersonal and too long to type repeatedly, so I will refer to him as “Mr. Payload”
The thing that screams, “Fake!” the loudest is the video snippet that indicates a cable attached to Mr. Payload’s harness. I notice that he also starts tumbling, as one might expect from a torque from the rockets, but this motion does not continue — something that a guide cable would interrupt. There’s also the trajectory analysis, which doesn’t jibe with expectations.
Rhett does a quick energy analysis of the maximum height, but the analysis assumes all of the energy goes into Mr. Payload and his rocket shell, thus giving an absolute maximum height, and the number he gets isn’t realistic. One must also consider the large amount of energy contained in the expelled water that generates the thrust to get a more realistic limit, as well as the energy used for the forward motion.
Rhett uses 1L of water per bottle , but to me it looks like there is more. I’m going to assume 20L of water but the same energy (i.e. higher pressure) and that Mr. Payload has a mass of 60 kg, which is more than Rhett uses but makes the math easy. Since the water is expelled quickly — it appears to be gone before he’s more than 2m above the dock, so I’m just going to model this as an explosion, with the water getting an impulse and Mr. Payload getting an equal and opposite impulse. Their kinetic energies must add to the total energy of the system, of 27kJ.
We have the sum of the KEs totaling 27 kJ, with \(KE = p^2/2m \) and equal magnitudes of momentum.
Solve for momentum, and I get 900 kg-m/s, or a speed of 15 m/s for Mr. Payload. If launched at ~30º, as in the video, that’s a height of under 3 meters, ignoring the considerable drag. It also means that about 20 kJ of the available energy (i.e. 3/4 of it) went into the expelled water.
One of the comments links to a video which looks real. The launch is at about 3:15
One Spookfish Was Harmed in the Making of this Paper
Spookfish Sees Things Like Nobody Else Ever Has
Of all the animals in the world, the lowly spookfish has the oddest eyes — compound mechanisms that bear more than a passing resemblance to rearview mirrors.
The bottom half of its eyes point upwards. The upper half point downwards, and are backed with a layer of reflective guanine crystals that bounce a focused image into the retina.
The titular disclaimer comes from reading this:
Researchers tested the eyes by taking flash photographs from above and below a live spookfish, then dissecting its eyes.
(there’s also this article)
The Photon Push-Me Pull-You Update
Back in June I wrote up a post an the Abraham-Minkowski controversy, which concerns the momentum of a photon when it’s in a medium.
Depending on the assumptions one makes, one can show that the momentum increases or decreases inside the medium, and obviously both solutions can’t be correct. But for a long time it was unclear which assumptions were faulty, because it was such a delicate experiment to do.
I just ran across a post at Everyday Scientist, and the paper (based on the ArXiv preprint I cite in the link) was published last month … and there’s a video.
The researchers performed a second experiment with a longer fiber and continuous–rather than pulsed–laser light and found similar results. The tip of the hanging fiber moved sideways like a pendulum by about 30 microns, which agreed with the tiny force (less than a billionth of a Newton) that they predicted. The team also verified that thermal effects, such as heat expansion, would be too small to influence the fiber’s movement.
Just Checking
Possible Abnormality In Fundamental Building Block Of Einstein’s Theory Of Relativity
Physicists at Indiana University have developed a promising new way to identify a possible abnormality in a fundamental building block of Einstein’s theory of relativity known as “Lorentz invariance.” If confirmed, the abnormality would disprove the basic tenet that the laws of physics remain the same for any two objects traveling at a constant speed or rotated relative to one another.
[…]
The new violations change the gravitational properties of objects depending on their motion and composition. Objects on the Earth are always moving differently in different seasons because the Earth revolves around the Sun, so apples could fall faster in some seasons than others. Also, different objects like apples and oranges may fall differently.
I find it amusing that there are a bunch of relativity cranks who claim that relativity is treated as dogma. The reality is that it isn’t all that hard to find scientists devising tests of relativity of various sorts, whether it’s testing the predictions of GR or checking for anomalies such as this.
Of course, thus far whenever someone has devised a clever test like this, we’ve found that relativity is correct.
Beulah, Peel Me a Grape
And nuke it.
Things to do in a microwave #2: Create a plasma
It just so happens that grapes are about the size of the wavelength of microwaves, which is important. And grapes also have sugars, which make them into dielectrics. (There are other fun things you can do with grapes because of this). Both of those together make the coupled grape halves into a dielectric dipole antenna, which is just a fancy way of saying that the microwaves that hit one side of the cut grape will pass to the other side, in a very concentrated way. The result is that there is a huge voltage generated between the two sides of the cut grape. That voltage causes electricity to jump from one grape half to the other (”arcing”). This is what happens when you rub your socks on the carpet and touch the doorknob — that spark is electricity jumping from your hand to the doorknob. The difference in this case is that there is a HUGE voltage generated (3000 volts by one website), and that is enough to ignite the steam from the grapes into a plasma state (a glowing ionized gas, where the electrons have been ripped from the gas molecules by the high temperatures). You can capture this plasma in a glass, as in the video above (wow!)
And, of course, this is preceded by Things to do in a microwave #1: Find your microwave hot spots
In addition to the two methods Stephanie lists, you can use marshmallows or chocolate chips, and look for where the melting starts. And then you can eat the experiment. (Stephanie mentions marshmallows; I missed it)
Update: Not done yet! Things to do in a microwave #3: Ivory Soap Monster
Things to do in a microwave #3: Microwave a CD
#3? Should be #4. (I’ve brought the whole “Five is right out!” counting thing to Stephanie’s attention) There’s an image that shows some mini Lichtenberg figures, i.e. the little tree-like patterns the electrons make.
Wrong Way! Go Back!
Imagine a string of pearls. You can start a wave by wiggling the first pearl or the last; the waves can travel either way because each pearl is coupled equally to both neighbors. But researchers have lately become interested in “unidirectional” coupling, in which the force between neighbors only allows waves to move in one direction. This can be seen as an extreme example of anisotropic media, in which the wave speed depends on the direction. Computer simulations have shown how waves will propagate through unidirectional arrays, and researchers have built electronic circuits that exhibit unidirectional coupling [1]. But these circuits had only three “pearls” in the array–too small to see all of the wave propagation effects predicted in the simulations.
An Answer to the Eternal Question
“What happens when you hit a webcam with a particle beam?”
A web camera is placed into a particle beam to show visually the affects of space radiation on electronics. This video shows the particles striking the camera along with streaks due to high angle impacts.
It’s not explained why the impacts aren’t localized — is it because of scattering occurring in the air or in the webcam lens? I assume so, and also that the high-angle strike is due to a scatter very close to the CCD, though it could have been from a cosmic ray — you see effects of these in cloud chambers. (I’ve thought it would be a great idea to have a webcam on a cloud chamber, and transmit a live picture, but when I searched to see if there was one I came up empty)
It Was a Dark and Stormy Experiment
Mr. Faraday’s (most excellent) experimental researches in electricity (1831)
I started to investigate Faraday’s writings while working on a post about Edward Bulwer-Lytton’s novel The Coming Race, which quotes Faraday to justify B-L’s fictional source of energy, vril. This led me back through Faraday’s monumental collection of researches on electricity, a collection of over 25 articles published in the Philosophical Transactions of the Royal Society under the blanket title, “Experimental researches in electricity.”
Faraday is also appearing at Cocktail Party Physics
I’ve always had a soft spot for Michael Faraday, for any number of reasons, but one of those reasons is that he was a brilliant experimentalist with world-class instincts for investigating the behavior of this strange new phenomenon, and yet he possessed only rudimentary mathematical skills — something that hampered the broad acceptance of his concept of how electromagnetism worked.