Some water tossed on a hot griddle. 420 fps.
Baby's First Transistor
Landmarks: Birth of Modern Electronics
In June 1948, the Physical Review published a description of a novel electronic device that “may be employed as an amplifier, oscillator, and for other purposes for which vacuum tubes are ordinarily used.” That statement hardly begins to capture the importance of the transistor, which made possible technology unimaginable at the time. But the first transistor design never saw commercial success. A different design, unveiled two years later by a colleague and rival of the original authors, spawned the modern microelectronics revolution.
Interlude
I’m off to DAMOP. I’ve got a few posts in the queue, but other than that I’m probably diving deep and going silent until next week.
In the meantime, have some Jell-o shots. (1000 fps)
(update: I don’t know what the interference is there at the end — it’s not on the original. I’ll upload the video again when I get back)
Update II. Done. The same problems persist in the uploaded video.
No, He Didn't
Am I on the ring road? Stunt driver defies gravity on the world’s biggest loop-the-loop
He didn’t defy gravity — I’m sure it was there the whole time.
If stuntman Steve Truglia had been too timid in his acceleration, his yellow Toyota would have reached the top of the track and dropped like a stone.
Not quite. If his speed was insufficient, he would not have reached the top. But the car would have dropped like a stone.
The Toyota had to be travelling fast enough that the centripetal force generated by its circular motion ‘offset’ the downward pull of gravity. This required the stuntman to enter the loop at exactly 37mph, immediately change out of gear and slow to 16mph as the vehicle swung round the top.
Well, no. The centripetal force is the gravitational force in the limit of the slowest speed that allows you to complete the loop, and the speed will naturally decrease as kinetic energy is converted to potential energy. Since the loop is 40 ft tall, we can actually calculate this. An object entering the loop and rising 40 feet to be traveling at 16 mph must be going 38 mph as it enters. The article says 37, but car is a little off the ground, so the actual change in potential energy is smaller. (The actual change in height is 37.4 feet using those numbers, putting the CoM a little over a foot off the ground. Close enough)
The downshifting isn’t there to slow the car down — the only thing the engine needs to do is compensate for losses. The downshifting is because the car will slow down, and you don’t want it to stall as the result of being in the wrong gear. An ideal car (of which a Toyota does not qualify) could simply coast after entering the loop. It’s entirely possible to enter the loop at a slower speed, but have the engine make up the additional energy needed while in the loop, but that would not have been the safe move from the he-doesn’t-so-much-loop-as-plummet angle .
And, from a physics point of view, he could have gone faster. 16 mph gets you about 1g of downward acceleration, i.e. you are basically in freefall under that scenario. The numbers don’t quite jibe — even when I use the smaller radius from above, the acceleration is a little lower than 1g. So undoubtedly some rounding went into the story already. Going faster would just mean that the track was exerting some force on him while at the top.
As far as the danger of blacking out, that’s why he wanted to be going near the minimum speed at the top, because near the bottom is where he would pull the most g’s — about 5 of them, at that speed, assuming the track is circular and not flattened to reduce the force.
That Nougaty Galactic Center of the Milky Way
Rotating Out of the Imaginary Plane
Commentary: Let’s get real about alternative energy
Lots of good stuff, including some tips that quantify some suggestions for efficiency,
Take, for example, the idea that one of the top 10 things you should do to make a difference to your energy consumption is to unplug your cell-phone charger when you are not using it. The truth is that leaving a phone charger plugged in uses about 0.01 kWh per day, 1/100th of the power consumed by a lightbulb.
This means that switching the phone charger off for a whole day saves the same energy as is used in driving an average car for one second. Switching off phone chargers is like bailing the Titanic with a teaspoon. I’m not saying you shouldn’t unplug it, but please realize, when you do so, what a tiny fraction it is of your total energy footprint.
as well as putting the alternative power generation options into perspective. Fossil fuels are used because they have a high energy density and they are transportable. Alternatives will have shortcomings.
There’s also a comment about hydrogen — one must realize that hydrogen is a storage medium, not a source. i.e. you have to make hydrogen, so hydrogen = battery
Before I close, I would like to say a few words about the idea that “the hydrogen economy” can magically solve our energy problems. The truth is that, in energy terms, today’s hydrogen-powered vehicles don’t help at all. Most prototype hydrogen-powered vehicles use more energy than the fossil-fuel vehicles they replace. The BMW Hydrogen 7, for example, uses 254 kWh per 100 km, but the average fossil car in Europe uses 80 kWh per 100 km.
It's All Greek to Me
The brilliant young PhD student Ralph Alpher working with his advisor George Gamow were about to publish a major work about the origins of the elements after the Big Bang. In a burst of inspiration, Gamow invited the physicist Hans Bethe to include his name on the paper, even though he had not contributed to it at all. That way the paper would have been authored by Alpher, Bethe, Gamow, a play on the first three letters of the Greek alphabet alpha, beta, and gamma. It was a delightful pun, and their one page paper serendipitously ran in the April 1st issue of Physical Review Letters.
Random Laser
The Laser Glow of an Atom Cloud
A normal laser is essentially a gain medium inside a reflective cavity. The light is amplified by the medium as it bounces back and forth between the cavity’s mirrors. A random laser has no cavity. Instead, tiny “mirrors,” or scatterers, are added to the gain medium, causing photons to bounce around and become amplified by the medium, before escaping in all directions. For example, a container of micron-sized particles floating in water in which a laser dye has also been dissolved can emit laser light if pumped with external light. Random lasers do not require the same precise manufacturing as normal lasers, so they could be inexpensive to produce. Potential applications include digital displays, light emitting paints, and temperature sensors.
Not Sunspots
Compton Lecture: Steven Chu
The energy problem and the interplay between basic and applied research