I want the most precise answer possible. I had originally asked the question: Is it likely that anything in the universe, that is affected by gravity, travels in a euclidean straight line?
I’m sure it could happen by accident, occasionally for some distance. I was wondering what the effect of all the gravitational forces in the universe would have. I realize that is a wide open question, involving particles whose location becomes unknown for small periods and other physics phenomena that I am not going to attempt to characterize. I was counting something rolling on a track, as I assume it is impossible to make a track with a straight line in the euclidean sense. Also, I don’t know what relativistic effects could be involved, and what they do to the definition of a straight line.
I’m going to speculate here. This like many things comes from accepting as true, something heard. I imagine the motivation for someone to say it first was political. Possibly they did not attribute this to Rosa Parks, but presented it as a hypothetical case. Either way, or for some other reason it was said, and then repeated by someone to make a better story. Undoubtedly, political opponents of civil rights would claim that Rosa Parks was ‘manufacturing’ a controversy. This story would appeal to any person who gets tired and has sore feet. Once it gets repeated, and is repeated enough times, people who hear it accept it as true. This is how the ‘big lie’ works in politics. People who hear something more than once will accept it as true. The more times it is said, the stronger the perception of truth comes to the listener. Once public records show it, say in a newspaper article, then someone writing a text book or other educational tool may copy it, and cite the source. Because this was an event in history, it is easier to get into the culture than some other concepts. But not as easy as when a scientist gets a news splash for making an equally false statement. Also, once repeated often, it is a political disadvantage to correct it by those supporting the original truth.
As in many of the cases in this thread, the greatest problem may be removing it from the record. Even in scholarly journals, it is rare for anyone verify the credibility of a cited source. The citations build with each use, and can become nearly impossible to erase. But, over time, as this thread has shown, public awareness of the facts can grow the same way, and supercede the falsehood. Lets hope in every subject, that the factual accounts will win out.
This seems to tie into the public school mantra of ‘individual achievement’, the idea that individual action is a prime moving force in world affairs.
This is, primarily, a simplification effort: Rosa Parks, Jackie Robinson, and Martin Luther King, Jr., are all single people we can point to as the people who broke racial barriers, so we don’t have to bog down the lesson plan explaining the details of post-WWII civil rights activism in America. Hitler is famous, but never a word is mentioned of how the Brownshirt street gang terrorized voters in Germany and ensured results favorable to the Nazis. (That has a further implication that inter-War Germany was a functioning liberal democracy up to the point the Nazis came to power in a free and fair election. This is utterly untrue, but pointing out the flaws would damage the Moral Lesson: Voting Is Evil.) FDR told us to go to war against Japan and Germany and off we all went, without a hint of dissent or question, never mind the groups on both sides that struggled with the question of isolationism versus interventionism throughout the period leading up to Pearl Harbor.
This sidles into the Great Man Theory, which, to be fair, was a lot more popular than it is today. It’s political, of course, because everything is political (as per the official dogma), but it’s primarily a combination of laziness and limited school years. After all, history lessons must eventually give way to mathematics and physics and art and so on.
The tides still have huge problems. So basically what Galileo said was that the earth orbits the sun in a circle and rotates on it’s axis while doing so. This means parts of the earth are travelling in the direction of the orbit and are moving faster and others are moving against the motion of orbit and are moving slower. This causes sloshing which causes the tides. So we get a bunch of testable predictions. They are that there is one high tide a day, it’s at noon, and it’s always about the same height. He then needed to add a hack to explain why his theory doesn’t work. (I mean getting the number, timing and heights of the tides wrong would be pretty glarring to anybody who was actually familiar with them.)
The other weird business is that Kepler actually had an explaination that was on the right track, the tides are caused by the moon. However Galileo dismissed that as silly because he thought the idea of it exerting a force without touching the water as weird. (Guess Galileo never saw a magnet or experienced static electricity.)
But it could be a factor in spectators’ perception of ball curve, and hence a part of the phenomenon. I’m not saying it is, just that it could be.
If we’re going to factor in forces from all over the universe then comparing motion to, say, planet earth seems arbitrary.
In other words, it will depend on your reference frame. Any path can be accurately described as curved or straight depending on the reference frame chosen. And there does not appear to be an ultimate “correct” frame.
w.r.t. the OP, great thread.
Even though I went to a lousy school I’m struggling to think of anecdotes right now.
The only one that comes to mind is when we were told that fainting was a deliberate mechanism to improve bloodflow to the brain (i.e. by falling over). Even at the time (I was about 11) I thought that was daft.
In other words, as the ball gets bigger, it fills a larger portion of your retina. Thereafter any minute eye movement may cause a shift from fovea to periphery and thus the illusion.
I’m afraid I only skimmed this thread, so I apologize if someone already mentioned it, but…
When I was in elementary school, we had an experiment in our science class to see if we could map out the taste receptors on our tongues. We used salt and sugar and tried to see if we could feel which parts of our tongue were tasting which substances. I couldn’t tell which part of my tongue was tasting what, and I didn’t get a good grade…
OK, I though that might be the type of answer. If there were some reasonably large volume of space somewhere out in the ‘dark between the stars’, say one light second in diameter that contained no matter at all, is there any frame of reference that would not depend on matter outside that big empty space. That may not even be a sensible question, but I’m trying to get to the human ‘frame of reference’ to begin examing this. Or perhaps its pointless to think about, something else I’d like to figure out before spending much time on it.
I don’t quite get the question to be honest. It’s not important whether there is any matter around. The point is that reference frames are arbitrary.
I think it’s because the assertion that there is an absolute, privilaged reference frame leads to a contradiction. It’s something to do with the fact that the force felt under acceleration and the force caused by gravity turn out to be manifestations of the same thing. Or something.
(I may have to disappoint you at this point: No, I’m not the ghost of Einstein)
So any path is straight or curved depending on whatever reference frame you choose to view it from.
I thought that by definition movement along a curved path meant that you were accelerating. It might be relative whether the acceleration is caused by gravity or not but there is no reference frame where an accelerating object is not accelerating. Perhaps what you’re thinking of is the idea that a body moving freely under the influence of gravity is traveling on a geodesic through spacetime?
I remember in the third grade taking a quiz in which “What is another name for cooking oil.” was asked.
I answered “vegetable oil”. I was marked incorrect. The correct answer was “salad oil”.
When i odjected, the teacher said, “On page 37 in the textbook, it clearly states cooking oil also sometimes called salad oil.”:dubious:
Later that year, we were told by some “metereologist” that the reason hurricanes were named after only girls was that girl’s names were easier to remember. :dubious::dubious: Of course, this also appeared on a quiz.
We were also quizzed on stuff that that had no revelance to living here in Hawaii like about radiators, chimneys, furnaces, coal, heating oil, snow.:dubious::dubious::dubious:
OK so the first two are a bit stupid … but what’s wrong with the third?
Were they wrong to underestimate how insular Hawaii is, and think that someone might one day leave? Or perhaps that it’s nice and useful to know about such things, even if you won’t personally use them?
I forgot about the geodesic concept. Does that mean in some sense everything travels in a straight line without a force other than gravity acting on it. And also, is there a way to specify the location of a point in the universe, other than relative to some specific thing like the earth? Sorry if I sound dumb on this topic, but I’ve forgotten the details of the few things I’ve known about it.
Correct; all objects follow geodesics in spacetime unless acted upon by a non-gravitational force. Note, by the way, that the spacetime part is crucial: If you just look at the spatial part and ignore time, it won’t necessarily be a geodesic.
Nope. Your reference point doesn’t need to be a specific object like the Earth (you could, say, pick the center of mass of the Earth and some planet around another star), but you have to pick something.
Why not? Kneeling to drink is extremely awkward for quadrupeds, and would leave them even more vulnerable to predators than they are now. All the other ruminants, and I’m pretty sure all quadrupeds, have necks long enough to be able to drink without kneeling.