Legend has it that if you say “Bloody Boltzmann” into a mirror thirteen times, Bloody Boltzmann will appear in your vacuum system.
Category Archives: Physics
A Spoonful of Silicon Helps the Medicine Roll Off
This superhydrophobic coating is truly stunning
NeverWet is a patent-pending silicon-based covering that deflects nearly all liquids and heavy oils by creating a very high contact angle upon application. The angle is much higher than traditional substrates, such as car wax (90 degrees), Teflon (95 degrees), or Rain-X (110 degrees). Liquid literally glides off NeverWet’s 160 degree to 175 degree angle in a way that almost seems like computer animation
I Hate You, Neil Tyson!
Neil deGras(Se) Tyson and The Inconvenient Truth
I like the image of Neil deGrasse Tyson popping up in unexpected places to inject some science into a conversation, and the suggested reaction (or phobia) is not entirely without precedent.
That's a Long Way for a Jaw to Drop
JAW DROPPING Space Station time lapse!
Click the HD and watch in full-screen.
I'd Buy That for a Dollar
There’s a DIY explanation at Cute video of kids DIYing their own penny battery, where I saw the video, but I found a higher-resolution copy, along with some other DIY battery projects, in this pdf
That's How I Roll
The how-to-build article, which includes a link to a paper describing the math and physics behind the phenomenon.
I Feel That Ice is Slowly Melting
This has already led to rapid growth in solar installations, but even more change may be just around the corner. If the downward trend continues — and if anything it seems to be accelerating — we’re just a few years from the point at which electricity from solar panels becomes cheaper than electricity generated by burning coal.
And if we priced coal-fired power right, taking into account the huge health and other costs it imposes, it’s likely that we would already have passed that tipping point.
But will our political system delay the energy transformation now within reach?
This Clock Has Stopped
Norman Ramsey Dies at 96; Work Led to the Atomic Clock
In 1949, Dr. Ramsey invented an experimental technique to measure the frequencies of electromagnetic radiation most readily absorbed by atoms and molecules. The technique allowed scientists to investigate their structure with greater accuracy and enabled the development of a new kind of timekeeping device known as the atomic clock. Dr. Ramsey received the Nobel Prize in Physics in 1989 for both achievements.
I had the privilege of meeting him and hearing him at a few talks where he told stories of the old days (I thought perhaps he was working on a book). Here is a picture of us at a conference in Seattle in 2005, where I am showing our nascent clock’s “Ramsey fringes” results to him — an interference pattern from the spectroscopy technique he pioneered — along with the clock stability results.
(photo credit: Tom Van Baak)
I Knew I Could, I Knew I Could
This Model of Stephenson’s Steam Engine was made in 2008 by master glassblower Michal Zahradník.
One nit: at about 1:40 it says to notice the steam exhaust — steam is water vapor and is invisible, so you can’t notice it. That’s one reason that steam line ruptures are so dangerous. If you can see it then the water has begun to condense; what you can see are small water droplets.
The Magdeburg Thermos Container
A comment from the slacktivist
Sometimes I can’t get the thermos open. This is frustrating because: A) There is coffee in the thermos, and I want coffee; and B) I twisted the thermos lid shut myself, and thus it seems logical to expect that I should also be strong enough to untwist it myself.
…
Oh, and as for the thermos, I find running hot water over the lid for a bit usually does the trick.
Logic? Nay, it is basic thermodynamics is the problem, and solution, here. A thermos is a good insulator — a vacuum is an excellent barrier against conduction and convection, but it’s not perfect — and you still have radiation. So the coffee cools, and since you likely left an air gap in the container, the pressure of that air is going to drop along with the temperature. PV = nRT. The volume is fixed, and we can assume n is not going to vary too much — the air will likely have 100% relative humidity fairly quickly after the thermos is sealed. As the system cools some small amount will condense, but to first order I’d expect it to be a linear relation. Even a small container with a diameter of 7.5 cm (~3 inches) has a surface area of ~44 cm^2 (7 square inches). For each 1ºC drop in temperature of hot water, that’s about a 0.003 (0.3%) drop in pressure, which is about 1.3 N of force, or 1/3 of a pound. So what of the temperature has dropped 10 degrees? This problem is amplified for larger caps, since it depends on surface area — a 4-inch cap will give you a half a pound per ºC.* On a sealed container with less structural integrity and/or sufficiently large surface area, cooling a liquid/gas mixture inside can lead to the container collapsing.
And it gets worse because the coffee is probably making a good seal of the threads — some air might have escaped when it was closing but now it can’t get in, so now you are trying to increase the volume which causes a further drop in pressure. More work that your hands have to do. This actually is more of a problem when you’ve filled the container up, since the relative change in volume is larger. A container that’s mostly filled with air will see only a small increase in the volume, but one filled with coffee might require that the volume double, meaning the pressure has to drop in half (roughly — water will evaporate at the lower pressure to mitigate this). So this might be responsible for a several percent drop in pressure, corresponding to several pounds of force on the cap.
The net result is that you are pulling against a vacuum (poor quality from a lab perspective, but that’s just a matter of magnitude) This is a version of the Magdeburg hemisphere experiment.
Heating does two things: it increases the pressure inside, and if you are heating the container faster than the cap, the differential expansion can allow some air to get inside to equalize the pressure.
* I really shouldn’t mix units like this, but being from the US I still think of weight and force of everyday events in terms of pounds.