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The hammer-feather drop in the world’s biggest vacuum chamber [video]

thekidshouldseethis.com

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Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#111

Post by bweitzman »

josu wrote: post #77
gradi3nt wrote: post #62

Earlier quoted context omitted.

Imagine being inside of a closed box like an elevator. Without leaving the box there is no way to tell the difference from being in free fall towards Earth versus floating in interstellar space. Therefor, general relativity take the perspective that gravity is a fictitious force (like centrifugal force) that arises from the shape of spacetime.

>versus floating in interstellar space 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

gradi3nt had it right

Free fall feels like floating Standing still (in the presence of the Earth's gravity) feels like being accelerated.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#112

Post by paddyoloughlin »

shangxiao wrote: post #75
paddyoloughlin wrote: post #17

I wish the producers were less enamoured of their slow-mo and showed us the whole thing in real-time. The "weird" thing is seeing feathers plummet to the ground and I wish we got to see more of that.

I actually like the slow-mo as it reaffirms the fact that there is no air in that chamber. 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.

I'm not against them using slow-mo at all.

But they showed the drop several times, and I would have preferred them to show it at real speed at least once.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#113

Post by vacri »

sambeau wrote: post #38
oneeyedpigeon wrote: post #29

Earlier quoted context omitted.

I find it interesting that Brian Cox, the presenter and avowed scientist, obviously finds it so 'surprising' as well. Maybe that's the true meaning of being a scientist, though - he doesn't truly believe it until observing it with his own eyes.

>Brian Cox, the presenter and avowed scientist, 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…

Still, I wish he'd use SI units, instead of things like 'cubic feet'.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#114

Post by vacri »

IgorPartola wrote: post #87

Serious question: why do we keep repeating this experiment? Not that I mind, I just am curious why do we keep building bigger and bigger vacuum chambers just to drop a feather and a hammer over and over.

Before they pump the air out in the video, the presenter explains what the facility was made for and is currently used for.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#116

Post by colomon »

anigbrowl wrote: post #103
mkagenius wrote: post #101

Earlier quoted context omitted.

> but you can derive almost as much experimental entertainment by dropping, say, a ping-pong ball and a similarly sized marble or ball bearing. in a vacuum chamber, right? In air they wouldn't behave same.

Ping-pong ball was a thoughtless example, but many things of different weights will be Good Enough for the junior experimenter, eg plastic ans steel pipe sections dropped straight downwards.

I demonstrated it to my son this morning by filling up one of two boots with coins and demonstrating both boots still fell at the same speed despite the weight difference.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#117

Post by gus_massa »

4ad wrote: post #79
gus_massa wrote: post #59

Earlier quoted context omitted.

There are two slow motion initial drops closeups: * 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, becau…

(Hope the Unicode math symbols appear correctly. ) > 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 dr…

I think that your model is correct, but I think that it's possible to add a few simplifications.

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.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#118

Post by mfisher87 »

anigbrowl wrote: post #93
antimagic wrote: post #57

Earlier quoted context omitted.

What? No! I don't know about you, but I would have a silly grin on my face too if I actually got to see this experiment live - I mean it's such a classic result - we've all been told that this is what would happen, but very few of us actually get to see it. It's like the experience of seeing the moons of Jupiter the first time that you look at it through a telescope - yes, you know the moons are there, you've even se…

I find this perplexing. Obviously few of us would get to see a feather drop due to the lack of a huge vacuum chamber, but you can derive almost as much experimental entertainment by dropping, say, a ping-pong ball and a similarly sized marble or ball bearing. 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 thin…

The demonstration that air resistance is the cause of the difference in fall duration is what you gain from this. You don't get to remove air resistance from the equation in any other way. It's easy for an ignorant person to assume there's no way air, something we "feel" no resistance from in our daily lives, would be able to fight the force of gravity to such a degree. This experiment makes that concept clear, where dropping a stick and a lead pipe from equal height would not.

Re: The hammer-feather drop in the world’s biggest vacuum chamber [video]

#119

Post by lobster_johnson »

anigbrowl wrote: post #94
smackfu wrote: post #82

Earlier quoted context omitted.

I think the backlash against Cox is almost cliché at this point.

I'd never heard of him before this morning, but this style of overly-polished TV production is common in the US as well. One of the things that irritates me about it is that they expend significant budgets on presenting and dramatizing quite basic things in science (which is a good thing) but all this experiential/eye-candy stuff comes at the expense of covering less material.

If you're looking for science documentaries with a little more depth, look at the series done by Jim Al-Khalili (eg., "Atom", "Absolute Zero" or "Chemistry: A Volatile History") and Michael Moseley ("The Story of Science").

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.

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