Category Archives: Video
Speed Reading
A library of high-speed physics videos wmv files
Cleanup on Aisle Six
Here we have a beautifully illustrated example of Newton’s First Law of motion involving shopping carts. Did some force push those carts out the back end of the trailer? Not at all.
Well Blow Me Down
Over at Good Math, Bad Math, Mark has a takedown of a device purported to move directly downwind, faster than the wind. Wind-Powered Perpetual Motion (and Dave Munger thinks he’s wrong.)
Here’s the video
The objection is simple: when you are traveling at the wind speed, there is no more wind in the cart reference frame, so there’s no force. The treadmill analysis is flawed.
If you’re testing a wind powered vehicle, then in a closed, windless room, putting the vehicle on a treadmill moving at 10mph is not the same thing as putting the vehicle on a stationary surface in a 10mph wind.
By putting it on a treadmill, you haven’t recreated the real-world situation — you always have your wind, and the treadmill doesn’t remove that. You never test the condition of having the wind relative to the cart drop to zero. So while it’s not faked, it’s still a sham.
It shouldn’t be hard to engineer a device such that the wheels rotate faster than the propeller, i.e. whatever the propeller’s rotation rate is for a wind of speed X, the wheel edges move faster than X. Since the wind is always present, the cart will move forward on the treadmill moving at X. Even uphill.
My question is this: if this works, at what speed does the cart stop accelerating?
UPDATE: Or with no wind present, as in the test (On the first viewing I thought they had a fan turned on) what you’re doing is converting treadmill kinetic energy into propulsion by turning the propeller. But you don’t need to have much propulsion to move forward, even uphill. Not a valid test.
Update, Mark II. See the comments — I was viewing this from the mistaken notion that the propeller was acting as a turbine while on the ground and at low speed, which isn’t the case.
This has the implication, I think, that the cart must have enough mass to ensure that the propeller acts as a propeller. My question of what the maximum speed is still stands, because I’m sure it involves fluid mechanics and that’s not something I’ll win should I tangle with it.
It … is … ALIVE!
We already know that cornstarch and water mix to make a non-newtonian fluid. Here’s what can happen when you stress and relax it rapidly (where rapidly is 80 Hz)
Strobe! Camera! Inaction!
Strobe light and falling water droplets
Dirty Rotten Scoundrels
You see a lot of interesting things working the night shift in a sketchy neighborhood. I constantly saw people making bad decisions: drunk drivers, gang members, unhappy cops, and con men. In fact, I was the victim of a classic con called “The Pigeon Drop.” If we humans have such big brains, how can we get conned?
It seems that reciprocating trust is an element in being conned.
My laboratory studies of college students have shown that two percent of them are “unconditional nonreciprocators.” That’s a mouthful! This means that when they are trusted they don’t return money to person who trusted them (these experiments are described in my post on neuroeconomics). What do we really call these people in my lab? Bastards. Yup, not folks that you would want to have a cup of coffee with. These people are deceptive, don’t stay in relationships long, and enjoy taking advantage of others. Psychologically, they resemble sociopaths. Bastards are dangerous because they have learned how to simulate trustworthiness. My research has demonstrated that they have highly dysregulated THOMASes.
(THOMAS = The Human Oxytocin Mediated Attachment System)
Here’s how a con works, which they also call the Pigeon Drop. Alternately, you can watch the beginning of The Sting, where they call it “The Switch”
Here’s the Three-card-Monte and Matchbox game. I know people who have fallen for this kind of con, and I recall someone trying to hustle me (and some friends) after a pickup basketball game.
You can’t win these games.
Möbid Curiosity
Möbius transformations.
via Ovablastic
Ice, Ice Baby
“Instant ice” from a supersaturated solution.
Acid Trip Illusion
Whoa.
When it tells you to look away at the end, look at something with contrast and texture, like with lettering. Not the wall. You can keep looking at the video — the effect you see is in your mind, not in the video.