From "
http://stupac2.blogspot.com/2006/09/6-commonly-believed-things-that-are.html"
1. Centrifugal force
There is a lot of confusion about this one. Some people think that the centrifugal force is what causes water to stay in a bucket when you spin it around or pushes you against the door when you take a sharp turn in your car. That’s completely wrong, but not helped by its name, which means “center fleeing”. Some people also call centrifugal force a fake force. This is also wrong. So what’s going on?
When something moves in an circle, it is accelerating. This acceleration is called centripetal, which roughly means “pointing toward the center”. Because acceleration is a vector, it needs a direction, and centripetal acceleration is always pointing toward the center of the circle, hence its name. Thanks to Newton, we know that F = ma, so when a mass accelerates there’s a force. But that force is not what pushes you out, because it’s actually pointed toward the center of the circle. So what’s going on?
Well, Newton also explained this one. What pushes you out is Inertia. Because your body resists changes in its direction, when it undergoes centripetal acceleration it wants to keep going in a direction tangent to the circle. That’s what pushes you against the door and keeps the water in the bucket.
So what about the “fake force” part? Well, in a normal reference frame, the centrifugal force doesn’t exist. But in a rotating frame, it most certainly does. So while we might not need it most of the time, examining forces from a rotating frame requires it. It’s not fake at all.
2. The sky is blue because of the ocean or space.
I cannot confidently say that this is a common belief everywhere, and I sincerely hope it isn’t, but when I was in high school a large number of people did believe it, and no one knew what really makes the sky blue. I won’t even go into why it’s idiotic to think this, because it’s so obvious, but the real cause is interesting and not very well known so I will elaborate on it.
The cause is known as Raleigh scattering. What happens is that the blue wavelengths of the light from the sun are absorbed and then radiated by the gasses in the atmosphere, while the rest of the spectrum remains unaffected. This radiation happens in all directions, meaning that the entire sky looks pretty much the same shade of blue. This is also why the sun looks yellow instead of white, enough of the blue end of the spectrum is removed for it to appear yellow.
It also affects sunset, causing more of the shorter wavelengths to be filtered out as the sun’s light has to pass through more of the atmosphere to reach you.
3. Extra Dimensions
Most people seem to think that extra dimensions are some kind of world parallel to ours, or at the very least have a very muddled understanding of what extra dimensions entail.
Extra dimensions simply entail more coordinates to specify a location in space. For example, in one dimension, only one coordinate is needed to specify an exact location, x. Two dimensions needs two, x and y, and three needs three, x, y, and z. For everyone but String Theorists, we live in a world of four dimension, x, y, z, and t. That’s all that it means when someone says time is the fourth dimension, you need to give a time of an event along with its location in space to locate it exactly.
Anything above four dimensions requires the extras to be “curled up”, which means that they’re very small, so small that the only things that can move inside them are the most fundamental particles of the universe. In string theory, they take the form of Calabi-Yau manifolds, which are extremely complicated mathematical shapes. They occur at every point in space, and to completely specify a location you’d need to also give the extra 6 or 7 (depending on the theory) dimensions.
4. Nuclear power plants can explode like a bomb
I know some extremely intelligent people who believe this, and it’s rubbish. Nuclear power plants don’t have anywhere close to the fissile material needed for the runaway reaction like a bomb. Modern power plants can’t even meltdown like Chernobyl did. It’s actually a great irony of history that the same day that Chernobyl’s reactors overheated the same test was done here in the US, and the reactor passed with flying colors. Safeguards in place today make overheating virtually impossible. The pollution from coal plants is far more dangerous than nuclear power ever will be, but people seem so irrationally afraid of nuclear power that it doesn’t matter that it’s the safest and cleanest means of generating energy (at least once we have a good waste disposal plan, and there are many in the works).
5. Microwave ovens (or other electronics) can cause cancer
No, they can’t, at least without some serious malfunction. They don’t release as much dangerous radiation as a slab of granite. The number one source of radiation encountered by most people (unless you get an X-ray) is the ground. Even if you were to microwave yourself, the radiation wouldn’t give you cancer because it’s on the low-frequency end of the spectrum, meaning it doesn’t have the energy to knock DNA apart, unlike UV, X, or gamma rays. Microwaves do heat up water nicely though.
6. Medieval people thought the world was flat
No, they didn’t. This was made up more or less out of thin air by Washington Irving in his horrid biography of Christopher Columbus. I haven’t the faintest idea why this has become so widespread, since there is ample evidence going against it, but unfortunately it’s still taught.
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