Category Archives: DIY science

Cans in a Blanket

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Rhett asks a straightforward question over at Dot Physics, in A blanket and cold stuff

Suppose you put take two identical cans of soda out of the fridge and place them on the floor in the middle of a room. One can you leave alone and one can you cover with a wool blanket. After an hour, you come back and check on the two cans of soda. Which will be warmer?

The reason I think it’s a great question is that it plays on a common misconception about thermodynamics, and it reminds me of a joke, and a related story.

The joke is about a person declaring that a thermos (which we often call a Dewar) is the smartest thing in the world. When it’s pointed out that all it does is keep hot things hot and cold things cold, the response is, “How does it know?”

Well, some years ago we were giving a tour of our lab to an Admiral (or Sneetch. I have taken to calling military lab visitors Sneetches, a Dr. Seuss creature. The high-ranking ones have stars upon thars) We mentioned the vacuum system, and the Admiral mentioned the lines from the joke — it keeps hot things hot and cold things cold, how does it know? My colleague was so focused in on explaining things, he didn’t recognize the joke, and started explaining the physics of heat transfer: a vacuum is a really good barrier to nonradiative heat transfer. I mentioned that it was a joke before he went in for a second round of explanation.

But the misconception — that blankets heat things up, rather than act as a barrier to heat transfer, is what is pointed out in this example.

New Ultra Toy

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A UV LED flashlight. Just checking on what fluoresces. Among the more interesting, we have the security stripe of a $20 bill

20billfluor

A Mr. Clean bottle shows both the label and the cleaner fluorescing

mrcleanfluor

and some vitamin B complex (I think the B-12 is the main culprit here), dissolved in some vinegar, and spilled on the counter in the shape of a guitar. Worship the fluorescent guitar!

vitbfluor

(I’ve previously noticed that vitamin B gives the appearance of remaining fluorescent even after digestion. Not that I’ve checked this with the flashlight. )

Call Him Neo

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MagnetNerd

Hi, I’m Rob Gallagher and I’m a MagnetNerd.

[…]

Neodymium Magnets are just plain cool. It’s totally amazing how something so small can have such strong magnetic forces. I enjoy showing others the amazing things that can be done with Neodymium Magnets. So far I have created 53 Videos of my experiments and designs on YouTube and have incorporated most of them into this website.

More magnet-relates stuff than you can shake a magnetic stick at.

Moving in Stereo

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Life’s the same, except for my shoes

Stereograms! Make Your Own 3D Camera for $15 or Less

If you happen to have two digital cameras, you can skip some of the steps, like getting the film developed and scanning the pictures. I was able to get my hands on a second camera; I found that butt-end joining got the lenses close together. I also tried side-by-side, using some optics posts and attaching to the camera tripod mounts. Unfortunately I did not have a third camera, so I can’t show the full rig.

Here is a laser table stereogram. I tested this on a few people, and not all could get it to work. But I can, and that’s good enough, for I am the benchmark for many things.

Tips for 3-D “cross-viewing”

Also, you can see that the two pictures appear to diverge from each other, an example of the leaning tower illusion

Deeper Than it Looks

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My recent post on Haidinger’s brush reminded me of another optical phenomenon I have observed, and one that is a bit easier to see: the Pulfrich effect.

The Pulfrich effect is a phenomenon that gives the illusion of depth based on the response time of different light levels in the eye and how the brain interprets the delay. Lower light levels take longer to process, so if the image viewed by one eye is dimmer than the other, the signal from the dimmer view will lag in reaching your brain to be interpreted. With one eye darkened, something moving across your field of view will appear to get closer or further way.

When I first read about this, I consulted Wikipedia, which tells me

In the classic Pulfrich effect experiment a subject views a pendulum swinging in a plane perpendicular to the observer’s line of sight. When a neutral density filter (a darkened lens – typically gray) is placed in front of, say, the right eye the pendulum seems to take on an elliptical orbit, appearing closer as it swings toward the right and farther as it swings toward the left.

Well, gee, I work in an atomic physics lab. I can make a pendulum and have neutral density filters, so I went ahead an made up the experiment, using some scrap wire and a few optical-mount bases for the pendulum. And sure enough, with the right combination of filters (I think I ended up with ND=0.3 or 0.4) I was able to easily see the effect — the pendulum’s oscillation got closer at one end and further away at the other, and it reversed itself when I switched and darkened the other eye.

I wanted to show this off, so to make things a little easier I salvaged a damaged pair of sunglasses and popped one of the lenses shades out. (Not really lenses are they? OK, pedantic man says they are, albeit with an infinite focal length) That covers the eye better than the ND filter, which only has a 1″ diameter. I can use either the free eyepiece or the glasses. The biggest problem is getting people to look with both eyes — their natural tendency is to shut one eye and only look through the shade.

Beulah, Peel Me a Grape

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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.

Things to do in a microwave #5: Microwave a lightbulb