It’s only a model (shh!) and spiders have eight legs, but … crap. Call Jim West and Artemus Gordon.
Category Archives: Video
The Mo is Slow
Thermal physics in slow motion
Almost makes me want to get one of those cameras. Almost.
Quality Time
Meet Entropy Jones. Four hours of a baby play, condensed into about two minutes of time-lapse video.
Sometimes You Can't Stop at 10
Not without a parachute and some good brakes, at least.
15 Ridiculous Rocket and Jet-Powered Vehicles
Here’s one: a jet-powered luge.
There’s also a recliner, shopping cart, an outhouse, and more silliness.
The the Impotence of Proofreading
Probably NSFW
Has this ever happened to you?
You work very horde on a paper for English clash
And then get a very glow raid (like a D or even a D=)
and all because you are the word¹s liverwurst spoiler.
Proofreading your peppers is a matter of the the utmost impotence.This is a problem that affects manly, manly students.
I myself was such a bed spiller once upon a term
that my English teacher in my sophomoric year,
Mrs. Myth, said I would never get into a good colleague.
And that¹s all I wanted, just to get into a good colleague.
Of course its impotent to note that four proofreading two bee effective in catching substitution errors, you have too actually know that you’ve used the wrong word, you looser.
Which Way is Which?
Omni-directional wheels.
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
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.
It's Much Better Than Cats
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)