Tag Archives: bad journalism

No, He Didn't

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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.

What an Entangled Web We Weave

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Even if we don’t practice to deceive.

zapperz has a post up which points to an article in the WSJ on quantum entanglement: Science, Spirituality, and Some Mismatched Socks

zz marks it as a good layman’s review, but I don’t agree.

Stranger still is entanglement. When two photons get “entangled” they behave like a joint entity. Even when they’re miles apart, if the spin of one particle is changed, the spin of the other instantly changes, too. This direct influence of one object on another distant one is called non-locality.

This is a common summary of entanglement, and it’s wrong. The entangled particles are in indeterminate states — the only thing you know is that the states have a particular relationship, e.g. one is spin up and one is spin down, or the polarizations are perpendicular, depending on how you entangled them. But the notion that one of the particles has a definite state before it’s measured is a classical interpretation, not a quantum mechanical one, and that’s where the analogies that are often used fail to work. That is, a particle prepared in this fashion does not have a state until it is measured — the state of the particle does is not “hidden.”

So if you don’t know what the state of the particle is, you can’t say that it has changed. What you can say is that when you measure the state of one particle, you instantly know the state of its entangled partner, but at the instant you do this measurement, the particles are no longer entangled. Further interactions affecting that attribute will result in no effect on the other particle. And I think this is where the quantum wheels come off the wagon, because this classical misconception has not been dispelled. There’s still this idea that the two particles communicate, and do so instantly. The description given gives the implication that this is so, and then you have the contradiction when you are told that faster-than-light communication isn’t possible with entanglement.

The amusing story of Bertlmann’s socks harms the explanation.

Mr. Bell noted that if he saw one of Mr. Bertlmann’s feet coming around the corner and it had a pink sock, he would instantly know, without seeing the other foot, that the second sock wouldn’t be pink. To the casual observer that may seem magical, or controlled by “hidden variables,” but it was no mystery to Mr. Bell because he knew that Mr. Bertlmann liked to wear mismatched socks.

For the story to work properly you have to also include the notion that which foot was sporting the pink sock wasn’t known until you measured it. All you knew was that one foot had a pink sock, and that if you measured it on Mr. Bertlmann’s left foot, you cannot say that it was on his left foot at any previous point. Thus is the weirdness of quantum mechanics and entanglement.

My take is that any article that puts forth such a basic misconception can’t be a good layman’s guide.

A better treatment

Perpetual Energy. Film at 11.

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Physics Buzz: Free Energy and the Press

Harlow mentions in passing that “Many scientists say the technology violates the basic laws of quantum physics.”

Really, such a sentence is tantamount to saying “It doesn’t work.” Unfortunately, that was lost on Harlow, who continued reporting as if the laws of physics could be changed with a simple majority vote in the local town council. Simply put the Universe doesn’t work that way. The problem here was this report aired at the same time that CNN announced it was closing down its entire science bureau.

Physics Malpractice

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Via physics and physicists I see a story about how golf can be hazardous to your hearing. And the story botches the physics. (I don’t know if it’s the journalist or from the original journal article)

The coefficient of restitution (Cor) of a golf club is a measure of the efficiency of energy transfer between the golf club head and the golf ball. The upper Cor limit for a golf club in competition is 0.83, which means that a golf club head striking a golf ball at 100km per hour will cause the ball to travel at 83km/h.

Well, that’s just wrong. The Cor tells you about the kinetic energy, so it won’t be the same for the speed, because KE depends on v2. i.e. if a ball is dropped from 1 meter and bounces, returning to 0.83m, the impact speed is ~4.4 m/s and the return speed is ~4.0 m/s, which is 0.91 of the speed.

Another problem is that the mass of the clubhead is not the same as the mass of the ball. Even if the Cor applied to speed, the statement is incorrect. In the limiting case of Cor=1 and the ball’s mass being negligible, the ball would leave at twice the clubhead speed.

The actual equation is v = u*(1+e)/(1+m/M)

v is the ball’s speed, u is the clubhead speed, e is the Cor, m is the ball’s mass and M is the clubhead mass. (This is trivially derived using conservation of momentum and balancing the kinetic energy equation to account for the loss) Using e = 0.83, and assiming the M=4m, we see that v = 1.46u

Update — This is using a definition of Cor on terms of energy. I couldn’t find how the USGA was defining it when I was composing the post, but further research (and noted in the comments) indicates that it is indeed the fraction of the speed retained after the collision. That changes the details of the analysis, but the article’s numbers are still wrong — the ball’s speed is larger than the clubhead speed. I still haven’t found a mathematical definition of how the USGA applies this to a golf club

That makes e in the equation the square of the Cor (so e = 0.689), which means that the ball leaves the clubhead at v = 1.35u

This May Not Bother Anybody Else

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… but it bothers a geek like me. Yeah, another leap second story. I suspect these will propagate, but like a game of “whisper” the errors will compound. Three…Two…One…One…Happy New Year!

They mention THE atomic clock (ha! there are many atomic clocks) and cesium clock/standard, but the picture is of a mercury ion clock. Not that anyone else would notice. Then there’s the mortal sin of the US Naval Observatory hyperlink going to the NIST cesium fountain wikipedia entry. (Don’t get me wrong — the folks at NIST do fantastic things and I have a lot of respect for them. And they’re fun at conferences. But get your links straight)

The blurb about miniature clocks goes to a link talking about optical clocks, which are nowhere near deployment as miniature devices. That’s purely conceptual at this point — full-sized optical lattice devices are cutting-edge at the moment, and require a fair amount of care and feeding. Miniaturization and making them robust enough to be portable, and work as true clocks as opposed to a frequency standard (a true clock runs continuously), is a long way off.

That's Dr. Time to You, Pal!

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Meet the world’s director of time

An interview with Dennis McCarthy, who is the Director of the Directorate of Time (or was at one point; I’m not sure how his retirement and subsequent resurrection affected the job title)

Though the BBC filmed in the lab, none of that footage made it into the embedded clip. Perhaps there’s footage in the show that’s airing on BBC 2, as I type this. I’ll have to check it out.

More than anyone, Dr McCarthy appreciates the need for the world’s population to be synchronised. But for those who don’t spend their working day checking atomic clocks, why is knowing the time so important? Think for a moment about how the GPS satellite navigation system works.

There is a network of over 30 satellites orbiting earth that broadcast a high-precision time-stamp down to the GPS system in your car.

These signals travel at the speed of light, which is very nearly one foot every thousand-millionth of a second – or one nanosecond (for the more metrically minded, that’s around 30cm, which is far less elegant. If there is a God, he built the universe using imperial measurements).

If that last part is true, God has a hell of a sense of humor.

The was one part of the embedded video that made me cringe, and that was the depiction of the Bohr-ish atom (with wavy orbit lines — is that supposed to make it all better?) and the electron making a transition between them. But in that representation, those are the levels described by the principle quantum number, and the transition of microwave clocks is in the spin state of the electrons, oscillating between spin-up and spin-down (whose energy degeneracy is broken because of interactions with the nucleus, which also has spin, and thus a magnetic moment) And the notion that you’re looking at radiation emitted by the atom is true in an active maser but not a passive standard like a cesium or rubidium clock — in those you make a separate measurement of the atom to tell you what state the electron is in.

(I don’t know if it’s a permanent link, but in the “In Today’s Magazine” column there’s Call him Mr Time . Hence the title, though I can’t actually envision Dennis saying that to anyone)

This isn't The Onion?

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Oh, wait. It’s just the time-honored (sorry, honoured) tradition of writing a headline that has the opposite implication than the actual story.

Call for creationism in science

Professor Michael Reiss says that if pupils have strongly-held beliefs about creationism these should be explored.

Rather than dismissing creationism as a “misconception”, he says it should be seen as a cultural “world view”.

Teachers should take the time to explain why creationism had no scientific basis, Prof Reiss said.
He stressed that the topic should not be taught as science.

Yeah, I can see how summing that up should be worded as a call for teaching creationism.

Focus, People

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This month’s Physical Review Focus: Nanoparticles Stick a Perfect Landing

They found that for speeds less than 1.2 kilometers per second, the nanoparticle bounces off the surface like a basketball. But at higher speeds, some of the nanoparticle undergoes a phase transition to a compressed state called β-tin, where each atom bonds to six neighbors. This transition is surprising, Dumitrică says, because the collision energy is not high enough to induce a phase transition in a macroscopic object. However, the impact force is applied over a few square nanometers, so the pressure inside the nanoparticle is extremely large–around 200,000 atmospheres, which is more than enough to cause the phase transition.

The β-tin state only lasts a few picoseconds, though. As the nanoparticle begins to bounce back, there is a second phase transition to an amorphous, or disordered, state. The combination of the two phase transitions, plus some heat generation, takes up all of the kinetic energy, and the particle remains on the surface. After all of this action, “the recoil is too weak to beat the adhesion forces between the nanoparticle and the substrate,” Dumitrică says.

However

A silicon nanoparticle flying at 8 times the speed of sound can slam into a surface and stick, but it bounces off if colliding at half that speed.

The speed of sound in what, pray tell? I wish journalists would remember (learn?) that the speed of sound is not a constant of nature.