XKCD has some good advice. Everyone should read the article ‘List of common misconceptions‘ on Wikipedia, if only so that they personally can stop spreading them.
There are a few on the list I have been guilty of believing myself at various points. The truth is:
- There is no evidence that Iron maidens were invented in the Middle Ages or even used for torture.
- Napoleon Bonaparte was not especially short.
- A belief that decades/centuries/millennia begin not on the year ending in 0, but rather on the subsequent year ending in 1 (e.g., “The current millennium didn’t really begin on January 1, 2000, but rather on January 1, 2001”) — based on an assumption that there was no year 0 — are founded in an incomplete understanding of historical calculation.
- Sarah Palin never said “I can see Russia from my house.” Palin actually said “They’re our next-door neighbors, and you can actually see Russia from land here in Alaska, from an island in Alaska.”
- Some cooks believe that food items cooked with wine or liquor will be non-alcoholic, because alcohol’s low boiling point causes it to evaporate quickly when heated. However, a study found that much of the alcohol remains – 25% after 1 hour of baking or simmering, and 10% after 2 hours.
- When a meteor lands on Earth (after which it is termed a meteorite), it is not usually hot.
- Different tastes can be detected on all parts of the tongue by taste buds.
- Although there are hair care products which are marketed as being able to repair split ends and damaged hair, there is no such cure.
- Sugar does not cause hyperactivity in children.
- A person who is drowning does not wave and call for help, as in fictional depictions of drowning.
- It is not nutritionally necessary to combine multiple sources of vegetable protein in a single meal in order to metabolize a “complete” protein in a vegetarian diet. Unless a person’s diet was heavily dependent on only fruit, only tubers, or only junk food, he or she would be virtually certain of getting enough protein if he or she were eating enough calories.
- It’s a common myth that an earthworm becomes two worms when cut in half. This is not correct. When an earthworm is bisected, only the front half of the worm (where the mouth is located) can survive, while the other half dies.
- The flight mechanism and aerodynamics of the bumblebee (as well as other insects) are actually quite well understood, in spite of the urban legend that calculations show that they should not be able to fly.
- Contrary to the common myth, the Coriolis effect does not determine the direction that water rotates in a bathtub drain or a flushing toilet.
- It is not true that air takes the same time to travel above and below an aircraft’s wing.
- Glass is not a high-viscosity liquid at room temperature: it is an amorphous solid, although it does have some chemical properties normally associated with liquids.
- No scientist ever lost his life because of his scientific views, at least to the knowledge of historians of science.
I have seen many of these repeated in rather reputable sources.
The Palin one stood out to me; she of course didn’t say “I can see Russia from my house.” For one thing, she obviously can’t. Tina Fey playing Palin in SNL is the source of the quote.
However, what Palin was trying to convey in her real statement is equally as dumb as the mis-attributed quote. She was explaining her foreign policy experience, claiming that she actually had some due to the geographical proximity of Siberia to Alaska.
The other one that stood out to me is the one about Coriolis force. My understanding is that toilets in the Southern hemisphere do flush in the opposite direction. What is the cause of this if not Coriolis force?
It is a common belief that the direction of rotation of a bathtub or toilet vortex is determined by the hemisphere it happens on. Whereas theoretically Coriolis forces affect the draining flow, in practice, various factors, such as rotation of the liquid, and basin shape, dominate, and the Coriolis forces are irrelevant.
How about the misconception, common among even experts, that drinking milk (or even taking calcium supplements) will stop the onset of osteoporosis…there is absolutely no conclusive scientific evidence that this is the case (nor could there be).
I will have to disagree with one of these points though “No scientist ever lost his life because of his scientific views, at least to the knowledge of historians of science.“
While the inquisition did not specifically target scientists, I am certain that more than a few scientists whose views ran counter to state or church doctrine paid the price with their lives. I would even argue that Socrates was a scientist as much as a philosopher….
I am still not positively convinced about Coriolis force. The experiment the Wikipedia article quotes is pretty amateur by today’s standards, and it was performed in 1908. Surely there must be a more definitive answer than that.
Besides, in a bathtub (which has no particular shape to impart an initial rotation to start a vortex in a particular direction) the vortex will always turn the same way, and stirring the water in the opposite direction will not cause a vortex to form.
Besides, in a bathtub (which has no particular shape to impart an initial rotation to start a vortex in a particular direction) the vortex will always turn the same way, and stirring the water in the opposite direction will not cause a vortex to form.
But do all bathtubs in each hemisphere have vortices that rotate the same way? If the cause is basin shape, angle, or some similar local phenomenon, the direction would differ.
Compared to the rotations that one usually sees (tires on a travelling automobile, a compact disc playing music, or a draining sink), the rotation of the Earth is very small: only one rotation per day. The water in a sink might make a rotation in a few seconds and so have a rotation rate ten thousand times higher than that of the Earth. It should not be surprising, therefore, to learn that the Coriolis force is orders of magnitude smaller than any of the forces involved in these everyday spinning things. The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD.
The direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. The magnitude of these rotations may be small, but they are nevertheless gargantuan by comparison to the rotation of the Earth. I decided to include a picture of a draining sink, and the first one I tried in my house was found to drain clockwise (the opposite of what the silly assertions would have it do here in the northern hemisphere). This direction was determined entirely by the way the tap filled the sink. The direction of rotation of a draining toilet is determined by the way the water just under the rim is squirted into the bowl when it is flushed.
According to my experiments:
Toilet – counterclockwise
Bathroom sink – counterclockwise
Kitchen sink – counterclockwise
Does anyone in the northern hemisphere have a basin that drains clockwise?
I’m happy about the experimenting this has led to. I just now tried two toilets, both flowed counterclockwise. I tried filling the kitchen sink with water and pulling the plug. In this instance, the vortex formed only right before the sink was entirely empty. As such, it was difficult to determine the direction of rotation. Still, I think it may have been clockwise. If such is the case, I may be eating crow.
I will be on the lookout in the upcoming days for clockwise turning drains.
For what it’s worth (which is not very much in a discussion about Coriolis force which is apparently dependent upon angular velocities), while the angular velocity of the Earth is small (one revolution per day) the surface speed of the equator is extremely fast by human standards ~1700km/h. While high supersonic airplanes like the mach 2 Concorde can outpace this speed and thus outrun daylight, it is still a significantly quick pace.
This speed is important for space flight because it is useful for achieving orbit. A spacecraft launched at the equator in the direction of rotation of the Earth would get 1700 “free” km/h towards its orbital speed and thus require less energy to get there. For this reason, space shuttle launches are from the very southerly Kennedy Space center, close to the equator by continental US standards. As well, the shuttle always launches largely eastward in the direction of the Earth’s rotation.
I checked in a bathroom sink; I was easily able to make the water rotate in either direction by stirring the water before opening the plug.
I did not know that Iron Maiden’s were a hoax.
As well, the shuttle always launches largely eastward in the direction of the Earth’s rotation.
Does that infinitesimally slow the rotation of the Earth with each launch?
Does that infinitesimally slow the rotation of the Earth with each launch?
This is pure speculation and not researched: Not necessarily, and in fact it might speed the Earth up. A rocket works by throwing hot gases quickly backwards. Because for every reaction there is an equal and opposite one, the rocket itself moves forwards. Therefore, a rocket firing in the atmosphere in the direction of the Earth’s rotation may well tend to impart a (tiny) rotation of the atmosphere opposite to the spin of the Earth thus creating friction of the atmosphere against the surface of the Earth whereby the Earth slows down.
Having said that, a portion of the time the rocket is firing outside the confines of the Earth’s atmosphere and not imparting any spin to it. Still, it is accelerating the shuttle. After the mission is done, the shuttle returns to Earth with all of its energy imparting a ton of energy to the atmosphere via drag in the direction of the Earth’s rotation. Finally it lands and brakes on the runway in an arbitrary direction imparting spin to the Earth in that direction. The landing energy is small overall compared to the drag of atmospheric re-entry.
Hopefully a NASA engineer or former physicist (Randall Monroe?) can jump in and explain if this is right or wrong.
I am told spinning counterclockwise slows the rotation of the Earth. I assume this applies only in the northern hemisphere.
I’m confused as to how that would work. You push off and start spinning, the Earth slows. You put your foot down and stop spinning, the Earth speeds up.
Imagine attaching a helicopter engine and rotors to the Earth. Just as the rotation of the blades in one direction turns the body of the vehicle in the other direction, the rotation of the blades would alter the angular momentum of the whole planet a little bit.
For the orbital launches, perhaps a good analogy is firing a cannon located on the equator. If you fired cannonballs in the opposite direction from the rotation of the Earth, you would speed it up a bit (if they went into orbit and didn’t land back on the planet). If you fired them in the same direction as the Earth’s rotation, I think it would slow.
RE helicopter:
When you shut the engine down, the friction of the slowing blades against the bearings in the helicopter create an opposite torque restoring the lost energy to the Earth.
RE: Cannon balls
But the balls (the shuttle) does land, and because the cannon (rocket gases) act on the balls (shuttle) partially while in space which doesn’t affect the Earth, I think the Earth speeds up upon landing.
Perhaps things that return to Earth have no effect.
I am pretty sure using a gravitational slingshot slows the rotation of the object you use.
When you shut the engine down, the friction of the slowing blades against the bearings in the helicopter create an opposite torque restoring the lost energy to the Earth.
The amount of friction when the blades slow down is constant, regardless of how long the helicopter has been running for, isn’t it?
You could run the engine for days and days, then turn it off. The total force expended during the operating time seems like it should exceed the opposing force during the slowdown time.
I love talking about this kind of stuff, but feel bad about having directed the thread away from the original point.
With the helicopter, there is a one time energy input into accelerating the rotor blades to the operating speed which is reclaimed as friction upon shut down. The rest of the engine’s energy goes into what is essentially combating drag; drag caused by the fuselage while it’s flying, drag from the blades rotating, induced (lift creating) drag from the blades producing thrust, etc. I don’t think that energy can be considered to be adding or subtracting to the rotating of the Earth.
Doesn’t the gravitational slingshot only slow the orbit of the planet around the sun? It doesn’t alter the spin of the planet about its own axis.
If you ran a helicopter engine and blades on the moon, what would happen? Where would the energy go, if it couldn’t be conveyed into air? I think it would alter the movement of the moon slightly.
Doesn’t the gravitational slingshot only slow the orbit of the planet around the sun? It doesn’t alter the spin of the planet about its own axis.
I don’t know. It seems conceivable that it could work either way. In either case, momentum would be transferred from a rotating system (planet rotating around axis or orbiting around sun) into momentum in a linear system (like a space probe getting launched out of the solar system).
On a related note, have you tried Phun? It’s a 2D physics sandbox, and quite entertaining to play with.
If you ran a helicopter engine and blades on the moon, what would happen? Where would the energy go, if it couldn’t be conveyed into air? I think it would alter the movement of the moon slightly.
Notwithstanding that a helicopter’s engine requires air to work (let’s assume an electric helicopter), the blades would accelerate to a higher speed than on Earth due to lack of air resistance, and then the predominant force the engine would be fighting would be internal friction, and in the case of an electric motor something called back EMF (basically electric motors are also generators and will only accelerate to the point that the input voltage is equal to the back EMF voltage that they are generating.) In this case all of the input energy would be released by the helicopter as heat.
In summary, I think even on the moon the spin is only slowed or accelerated a finite amount equal in energy to the kinetic energy of the blades while the helicopter is running, and the spin is exactly restored upon shutdown.
I haven’t tried Phun but will tonight upon your recommendation.
Would a vehicle driving on the moon be any different? For instance, an electric vehicle driving constantly around the moon’s equator.
Again, it seems like it would be imparting momentum bit by bit for as long as it was running, and would only reverse that a set amount if it stopped.
I think in that case maybe imagining the moon as a frictionless environment would be helpful. Maybe the “car” is actually a train running on a geared track so we can account for traction in the absence of friction.
While the train is accelerating under power, the moon is being slowed (or accelerated depending on the direction of the train). If at any point you disconnect the engine, the train will stop accelerating but continue at its present speed. At this point, the rotation of the moon is not being affected. When you decide to slow the train, the rotation of the moon will be restored.
If you decide to not disconnect the power, the moon’s rotation will continue to change, but the train will also continue to accelerate. I don’t know enough about relativity to know what happens near the speed of light, but ignoring those phenomena, the train would accelerate to ever increasing speeds. If the train is ever slowed, the moon regains its speed.
I don’t know. It seems conceivable that it could work either way. In either case, momentum would be transferred from a rotating system (planet rotating around axis or orbiting around sun) into momentum in a linear system (like a space probe getting launched out of the solar system).
I think the distinction is important because a planet orbiting a star is moving forward through space. The object being slingshot is subtracting some of the planet’s orbital energy and adding it to its own.
The spin of a planet (to my knowledge) doesn’t affect its gravity, and gravity is the important force in orbital mechanics. For instance, I don’t think satellites in space much care which way the Earth is spinning. Rather, they care that it’s exerting a force on them directly downwards, seemingly from its center.
“No scientist ever lost his life because of his scientific views, at least to the knowledge of historians of science.”
David Christopher Kelly an expert in biological warfare and a former United Nations weapons inspector in Iraq was either murdered or committed suicide, but in either case the cause was related to his views on the truth of the weapons-of-mass-destruction claim which was used to justify the Iraq war.
“No scientist ever lost his life because of his scientific views, at least to the knowledge of historians of science.”
I think this is debunked by the case of Nikolai Vavilov, who, according to wikipedia, was imprisonned (and died as a result) largely for his criticism of Trofim Lysenko’s ideas – centrally the idea that acquired characteristics of an organism could be inherited. Mendelian genetics was criticized for being bourgeois and overly determinist and reductionist.
http://en.wikipedia.org/wiki/Nikolai_Vavilov
Matt,
Do you think the XKCD comic about rotation is wrong?
That seems unlikely to me. The comic has hordes of fans, many of whom are physicists. Admittedly, that is an argument from authority rather than logic.
Tristan,
It may be splitting hairs, but I think there is a distinction between being imprisoned until you die and actually being killed because of your scientific views.
Also, lots of scientists have died in the course of doing scientific work. There are accidents, and facilities where scientists work are also targeted in wartime.
I think I certainly require clarification about the XKCD comic; perhaps it’s referring to different mechanics than what we’ve been discussing above.
Having said that, I accept Randall Monroe has (I think) a physics degree and is a very smart guy.
Each turn wouldn’t rob the planet of angular momentum. Starting turning would rob the planet, but then the only thing that would allow additional turns to rob the planet of more angular momentum would be drag with the air (and this effect would also plateau). As long as you’re turning, though, you would push back dawn… But once you stop turning, the Earth gets its angular momentum back.
The moment of inertia of Earth is:
I = 8.034×10^37 kg m^2.
Now, suppose we wanted to delay dawn by a total of 1 second, over the course of a 12 hour period (say, the entire night). The period of the Earth during that time would increase from 24 hours to 24 hours 2 seconds, or a difference in angular velocity of:
Δω = 2π/86400 – 2π/86402
= 2π(86402 – 86400)/(86402 * 86400)
= 4π/(86402 * 86400)
= 1.6833×10^-9 rad/s
This gives the difference in rotational inertia as
ΔL = IΔω
= 1.352×10^29 Js
The moment of inertia of a human body is much harder to find… the best I could find is a model which gives the moment of inertia around a vertical axis as around:
I = 1.5 kg m^2
Now, with the rotational inertia calculation above:
ω = L / I
= 9.016×10^28 rad/s
or 1.434×10^28 rotations per second.
And that’s assuming she’s standing on the north pole… if she’s standing elsewhere on the planet, you get confusing stuff in three dimensions… but I’m pretty sure she’d have to spin even faster just to get that one extra second.
Going the other way, assuming she spins about once per second:
ω = 2π rad/s
L = 4.189 Js
Δω = 5.214×10^-38
which comes to a difference in period of about 1.112×10^-48 seconds.
Now, you’ll notice that the speed in the first part would mean most of her body is travelling significantly faster than the speed of light, and that the time in the second is less than the Planck time. But since I couldn’t be bothered getting into relativity or quantum theory, that’ll do for me.
Sorry for the downer.
Milan,
I think you are splitting hairs. Dying of malnutrition in prison is murder by the state. Also, Vavilov was far from the only geneticist murdered for refusing to embrace the weird soviet turn to Lamarkianism.
The Murder of Nikolai Vavilov: The Story of Stalin’s Persecution of One of the Great Scientists of the Twentieth Century – 2008
http://books.google.com/books?id=2mi7NAOxe-8C&printsec=frontcover&dq=The+Murder+of+Nikolai+Vavilov:+The+Story+of+Stalin's+Persecution+of+One+of+the+Great+Scientists+of+the+Twentieth+Century&hl=en&src=bmrr&ei=yMYnTf-_C42WsgPrv7iiBw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCMQ6AEwAA#v=onepage&q&f=false
The Science of Genetics Under Stalin
by Dr. Farid Alakbarli
“By gaining favor with Stalin, Lisenko gained control of all agricultural science throughout the country, including all scientific institutions, universities and laboratories related to biology, genetics and agriculture.
Stalin embraced the ideas of Lisenko and it wasn’t long before he had Serebrovski and Koltsov shot to death. Vavilov was imprisoned and died of dysentery. Hundreds of other genuine geneticists and selectionists suffered during the Repression as well [especially during the year 1937]. ”
http://azer.com/aiweb/categories/magazine/ai131_folder/131_articles/131_genetics_stalin.html
“…facilities where scientists work are also targeted in wartime.”
Or, if you’re unfortunate enough to be Iranian, during “peace” time, which means time when your state is under constant threats of force, implicit and explicit, from the United States and its regional allies.
“The scientists were targeted by men on motorbikes who attached bombs to the windows of their cars as they drove to work, officials said.
The scientist killed has been named as Majid Shahriari.
President Mahmoud Ahmadinejad has accused “Western governments” and Israel of being behind the killing.
Another scientist was killed in a bomb blast at the beginning of the year.”
http://www.bbc.co.uk/news/world-middle-east-11860928
Science and religion: “No scientist ever lost his life…” and Lysenkoism
“No scientist ever lost his life because of his scientific views”
What about those whose (false) views led them to undertake fatal experiments? I’m sure there are probably plenty of examples.
I can’t find the reference to the calendar claim (your 3rd dot point) in the Wiki article. If this claim is correct, then I am repeatedly guilty of that one. I think I was aware of nearly all the others (though the iron maiden was news to me as well).
The claim about decades/centuries/millennia is now gone.
I don’t know what to believe about it now…