In the early 17 th century people argued that the earth can't be rotating because the don't feel any movement. How fast would the earth have to rotate for us to feel the effect of rotation and have no doubt of its rotation?
How fast would the earth have to rotate for us to feel the effect of rotation and have no doubt of its rotation?
There is a possible way of estimating this - or at least putting a lower limit on it. Consider life on a ship. The crew (even on a very small one) very soon get used to the curved courses that ships take and they easily cancel it out in their brains. The rate of turn on a large tanker is a lot faster than the Earth's motion and, more importantly, it is not uniform over time but I wouldn't mind betting that experienced crew would be able to detect some very slight course adjustments. To put a figure on it, perhaps 360°/hour would be too slow to be detectable (compared with 24hours we all experience).How fast would the earth have to rotate for us to feel the effect of rotation and have no doubt of its rotation?
Right: there is nothing to "feel" except the magnitude of the acceleration and there is no way to tell the difference between gravitational and rotational. If you're on a different planet with a 10% different apparent g, you might notice, but there's no way to tell by "feel" how much of that is gravity and how much is rotation.Let's put it this way: If the Earth was spinning fast enough so that it attained orbital speed at the equator, then objects at the equator would be "weightless". However this still only results in the Earth making 1 rotation in roughly 90 min. Could you easily detect that you were rotating that slow?.
So while you could deduce the spin of the Earth by traveling North and South and noting the difference in gravity as you did so, and this difference would be easier to measure as the speed of rotation increased, you still wouldn't be able to "feel" it when standing in one spot.
Wait a minute. Potential does not change with latitude. But the g you measure with an accelerometer is not potential. It is the [magnitude of the] gradient of the potential.Earth's surface is equipotential to the extent it fits the theoretical geoid. The g you measure with an accelerometer while sitting on Earth's surface does not vary with latitude:
Yes. The geoid will always be at right angles to the local direction of ##\vec g##. That's not the same thing as saying that it is a surface where local ##\vec g## has a fixed magnitude.Earth's shape is caused by that g.
I was thinking that mgh (Work) would be noticeable when lifting and climbing. Going up a slope is the equivalent of a bigger g. (I think that must be right) I wouldn't just be Weight Force that counts in general 'getting around' in a different g. But it al depends what the rules are to this particular game, I think.But we are not talking about any slopes. Just an equipotential surface -- flat and level.
When cycling, the bicycle takes care of the vertical load. Bigger g is irrelevant. Slope and wind resistance are the enemies. Good wheel bearings and properly inflated tires make rolling resistance (which can scale with g) largely irrelevant.Going up a slope is the equivalent of a bigger g.
I see what you mean - I shouldn't compare flat cycling with cycling up a slope. But two different slopes would be a valid analogue with the broader experience in different g conditions but we would have to define more precisely what we are comparing with what (before it's handbags at dawn time). Power is actually what counts in getting you exhausted and mg dh/dt has contributions from g and dh/dt. Or, if you carry extra weight up hill, of course. I know from my limited cycling experience that changes in slope are very noticeable, even when you are fit.Bigger g is irrelevant
True... so the change of velocity of 1000mph, over 12 hours I so slight of an acceleration that we couldn't feel it. is that better? (1.3mph per min, ave rate of change)Percentage velocity change is neither well defined nor observable. That's basic Galilean relativity.
Yes, that is better.True... so the change of velocity of 1000mph, over 12 hours I so slight of an acceleration that we couldn't feel it. is that better? (1.3mph per min, ave rate of change)
This question has much to do with human physiology and little to do with physics.
Human perception of acceleration has a big deadband. Flight simulators take advantage of that to give pilot trainees the illusion of unlimited motion even though the actual motion of the simulator is limited.
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