The hammer-feather drop in the world’s biggest vacuum chamber [video]
thekidshouldseethis.com
thekidshouldseethis.com
The "weird" thing is seeing feathers plummet to the ground and I wish we got to see more of that.
So no, I don't think that that's a fake grin. But then, as with most female geeks, I have a huge Brian Cox crush, so I may be biased ;)
Really, I think the slow-motion camera has much more educational value than the vacuum chamber (cool as that is). When I was in school and we'd debate such things, I liked to do experiments but dropping things of different weight off the roof only takes you so far, as people might object that they hit the ground a fraction of a second apart but too little of an interval to notice given the relatively low height etc. If I was doing it now I'd just use my camera to tighten things up, and although it's slo-mo capabilities are limited several current consumer models deliver that functionality at affordable prices.
in a vacuum chamber, right? In air they wouldn't behave same.
It's one thing to know that this will happen, it's another entirely to see it happen.
Ah, I guess anything that brings more viewers to science content is good. I just miss the old days of Horizon.
I really don't mind Cox... what I despise is the trend of putting comedians in to science and politics shows in an attempt to relieve the dowdiness (Sorry Dara). Then again, I'm one of those people who used to sneak downstairs in the early hours to watch the dusty math and science stuff the BBC used to broadcast for teachers to record on VHS.
Surely he's qualified to demonstrate F=ma, even to someone with a sense of wonder as evolved as your own.
It's motto seems to be "Look at us! We're scientists but we're so wacky!!!111"
Ben Goldacre is the master of this style of science communication. Friendly and fun and enthusiastic, but in a way that appeals to both laymen and his peers. I suppose epidemiology is somewhat more human than astrophysics, so its easier.
Kids are no, even though I know the relevant laws of physics and was intellectually not surprised, I was still in awe and it still violates my instinctive expectations. A visual equivalent to stepping onto a broken escalator.
In "The Story of Science", Moseley covers much the same ground as James Burke's famous "Connections" (and also his highly-esteemed "The Day thee Universe Changed") -- albeit in a more literal and less literary angle -- or indeed Sagan's eminent "Cosmos".
Al-Khalili is a physicist, though, and I think his documentaries are more to the point than Cox's, even if they're also full of excellent photography. Definitely less bubbly.
[1]: http://www.dailymail.co.uk/sciencetech/article-2819205/Testi...
When the feathers first drop you see a slight sway in the feathers, but only due to the acceleration. It's actually quite a sight to see feathers accelerate so quickly and stay so still.
But they showed the drop several times, and I would have preferred them to show it at real speed at least once.
But on closer viewing that is a disastrous montage: the first few seconds (before cut away) show the feathers fluttering and the bowling ball starting to accelerate away; the slow-motion segue is under vacuum conditions though. The film editor's intention is that the two shots appear contiguous. We can speculate why they might have done this (no close up shot taken under vacuum conditions?) but it really tramples the whole point of the article :(
This is true for the big ball too, except that the speed of sound is orders of magnitude faster in it, and the spring constant of the material (steel?) is also many order of magnitude larger than the spring constant of the feather.
The center of mass of both objects falls at the same rate. At t=0, d^2x/dt^2=0 for the points closer to the ground and d^2x/dt^2=2g for the points that were just unhooked. Also see https://www.youtube.com/watch?v=mAA613hqqZ0
After looking at it I agree with zwp, the editor really did make quite a mistake when assembling the last sequence.
[Edit: Screen grab of both http://imgur.com/EAKB5FK and I agree with the over all editing comment below. The slow motion shot as the first shot of falling in the vacuum was the thing that really stood out and I thought was bad on the first play through.]
* 2:52 -> http://youtu.be/E43-CfukEgs?t=2m52s
* 4:51 -> http://youtu.be/E43-CfukEgs?t=4m15s
The second one (4:51) looks like a drop in the air, because the barbules (the small parts of the feather) go "up" and flutter.
The first one (2:52) looks like an actual drop in vacuum. But I think that the oscillations are not related to the speed of sound in the feather, because I think that the sound travels too fast to be visible in this video. (I'd like to see some measured data.) I don't see waves traveling in the feather.
Initially the barbules hang down. After the feather is released, the feather is gravityless (in the non inertial reference frame) so the barbules go to their natural position, so they go "up", but only slightly and the flutter is minimal.
> After the feather is released, the feather is gravityless (in the non inertial reference frame) so the barbules go to their natural position, so they go "up", but only slightly and the flutter is minimal.
You're saying the same thing as I did in different words, in fact my analysis was also in the accelerating frame :-).
So, in the accelerating frame at t=0 (the drop), we have an deformed elastic object that acts very similar to a harmonic oscillator, with some initial deformation Δx. It's not exactly a simple harmonic oscillator because the mass is distributed throughout, and the effective mass is NOT the mass of the spring (in fact it's one third of that), but it's relatively easy to show it moves like one (to the first degree for small displacements), albeit not in a Hacker News discussion. It will move according to
D²[x] + 2ζωD[x] + ω²x = 0
Elasticity and sound waves are very closely related. Sound is a particular kind of wave traveling through an elastic medium. For an approximately linear object, we only have longitudinal waves that move with c=√(Y/ρ). Y is Young's modulus and ρ is the density. You can immediately see that small values of Y give rise to small values of c.
For ideal springs of length X and cross-section S we can prove that (exercise left to the reader) that:
Y = Xk/S
kΔx/S = Y Δx/X => F/S = Y Δx/X => Y = FX/SΔx
Plugging all values in we get Y=5248Pa. Speed of sound is c=√(Y/ρ)=c=√(Y/(M/V))=√(YSX/M)=4.58m/s, a very low value indeed and quite consistent with the slow motion video.
Just for kicks, the speed of sound in rubber 60m/s. It shouldn't surprise us at all that the speed in feathers is smaller than for rubber. Feathers are much weaker springs than usual rubber springs. (Note that if we had a spring made of rubber coils, the speed of sound in the spring would also be much smaller than the speed of sound in a rubber rod).
The approximations made above are all pretty wild, but the point I was trying to make is that waves travel quite slow in weak springs. The exact values don't matter. Just get yourself a long spring made of plastic or thin metal wire and create some waves. You can see the propagations, they move very slowly.
If the speed of sound is ~5m/s and the feather length is 0,2m then the time to for a signal to travel from one tip to the other is ~1/25s. That is approximately one frame in a standard camera (PAL/NTSC). So if they are using a standard camera, it's possible to assume that the drop signal travels almost instantly.
The system is totally overdamped, so I think that it's better to model it as a movement in a fluid with hight viscosity (like a spring inside honey). If you drop the acceleration term and you get
2ζω.D[x] + ω²x = 0
where 2ζω/ρ is something like the apparent viscosity that see a barbule moving inside the "fluid" of the other barbules.
The solution is
X = A exp(-ω/2ζ t)
So the relaxation time is ω/2ζ. When it's overdamped the system almost don't oscillates. Watching at the video, after it falls 1-ball-diameter the barbules reach the final position. I guess the ball is ~0,3m, so I guess that ω/2ζ ~= Sqrt(2h/g) = 0,8 seconds ~= 20 frames in a standard camera. But I have not idea about a sensible value for ζ.
https://news.ycombinator.com/item?id=8556363
The text of the site I submitted has kindly been posted by DanBC[0] here:
My guess is that it's a standard demonstration for visiting dignitaries and the like.
Now, they are recreating an experiment last performed at this scale on the moon. It's an unusual break from the norm, and I'm sure half of their grins were the phenomenal waste of power to perform such a silly experiment. (Seriously, that chamber was hauled down to a couple torr in three zarking hours!) Professionally goofing off is immensely fun.
(Tiddlywinks with a forklift would be another, and there was a guy who used the armor coating a Blackbird uses in a robot wars competition.)
They are used to the chamber and with experiments in the chamber, but this simple experiment with a feather and a iron ball is very different from what they usually see.
They probably usually see only heavy objects and mechanisms for space projects being tested there. Such a graphic and basic experiment must be well outside the norm.
Why do you say that? They could have easily made the apparatus for this experiment.
Here's the youtube link: https://www.youtube.com/watch?v=E43-CfukEgs
> If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
I think the guidelines are mis-guided in this sense. Sometimes the original, raw content is somewhere else, but a page that points to it can sometimes add context, or otherwise enhance that original post/material.
But this is meta, and getting off-topic. To go meta-meta, I do wish there were somewhere sensible to discuss these sorts of issues.
---begin quote--- …though in this case, “the hammer” is a bowling ball. In this [excellent clip]{https://www.youtube.com/watch?v=E43-CfukEgs} from the BBC’s [Human Universe: Episode 4]{http://www.bbc.co.uk/programmes/p0276q28}, Professor Brian Cox visits NASA’s Space Power Facility in Ohio, home of the [world’s biggest vacuum chamber]{http://facilities.grc.nasa.gov/spf/#}, to test Galileo Galilei‘s Leaning Tower of Pisa experiment, circa 1589:
[If you drop a brick and a feather at the same time]{http://www.planetseed.com/laboratory/galileo-drops-ball-virt...} the brick will probably hit the ground first. But this is because of differences in the amount of friction between these objects and the air around them, not because their masses are different. If there were no air…
What happens? How does a hammer, brick, or bowling ball move in comparison to the feathers when you remove any air resistance? Watch.
Then watch this next: Apollo 15 Commander David Scott famously conducts this [same experiment in 1971… on the moon]{http://thekidshouldseethis.com/post/31056368331}. ---end quote---
Versus being inside that an elevator that is being accelerated in interstellar space
This seems like a pretty good explanation: http://www.astronomynotes.com/relativity/s3.htm
Free fall feels like floating Standing still (in the presence of the Earth's gravity) feels like being accelerated.
But in seriousness, does the Moon not count? Surely space is the largest vacuum chamber we have access to!
I think you mean "Brian Cox: Professor of High-energy Particle Physics, member of the High Energy Physics group at the University of Manchester, and the ATLAS experiment at the Large Hadron Collider at CERN (who also presents popular science programmes in the UK)"
I think his career as a scientist deserves a little more recognition than "avowed".
And, as for his career in popular science he has been awarded both a Faraday and a Kelvin prize.
It is awesome to see something so un-intuitive but so well known actually occurring - like if you could actually see quantum tunnelling happening. If you don't find the world awesome then doing physics has got to be a pretty hard slog.
But then I'm over-awed just about every time I use a mobile [aka cell-phone] or computer at the physics and engineering that's happening, the maths being applied, ...
A computing equivalent might be seeing Babbage's Difference Engine[1] or a valve based computer at work for the first time - you know the maths, the algos work, you know the science well enough (certainly in the mechanical computers) but seeing it all chug away and produce the result has a certain enthralling beauty. Maybe it's more like seeing a visual emulator [2] working on assembly code? You know it works, you know why it works (at some level at least) but it's doing it, it's awesome!
Not that I advocate explosive decompression in any circumstance, mind you.
If you want to see more of it in video, it's also where the opening scene to "The Avengers" was filmed. Plum Brook Station has a whole collection of really cool (though mostly single-purpose) buildings.
It's appeared in a lot of movies, "Futureworld" (1973) being one of the first.
That's where the nuclear rocket upper stage for Apollo was supposed to be tested.
Now, if they hadn't developed it, someone else probably would, but perhaps not at that time - leaving us at years behind where we currently are with e.g. the speeds on our mobile devices.
Similar large facilities exist at many national labs, and they are used only sporadically. For instance, in the Bay Area, NASA Ames has a very large (11 foot square) wind tunnel that can reach Mach 1.45 (http://www.nasa.gov/centers/ames/orgs/aeronautics/windtunnel...).
The inflatable bags that landed Spirit and Opportunity on Mars were tested in Mars air pressure at the Glenn vacuum facility: http://www.nasa.gov/centers/glenn/about/history/marspbag_prt... . Many spacecraft undergo "thermal vac" testing meant to simulate space conditions.
But to answer a more general question. We shouldn't stop repeating experiments just because they were done before. The scientific method works as long as we keep reproducing results. Sure, this is a trivial result, but it's something every kid should have done by its own in the school physics lab.