# Tell us an interesting random fact you stumbled across (Part 2) **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [July 25, 2024, 3:06pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785 "2024-07-25T15:06:02Z")\ **Posts on this page:** 20\ **Page:** 125
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 3:02pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2481 "2025-05-26T15:02:39Z")
> [@Xocomil](#): > > However, falling under gravity doesn’t _feel_ like acceleration. Einstein says otherwise. No experiment can distinguish between being in a gravitational field and/or experiencing uniform acceleration. See: [Equivalence Principle.](https://en.wikipedia.org/wiki/Equivalence_principle) Put another way…gravity _feels exactly_ like uniform acceleration. The two cannot be distinguished. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [May 26, 2025, 3:48pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2482 "2025-05-26T15:48:00Z")
> [@Pleonast](#): > > General relativity uses geometry and frames of reference to describe the inertial motion of matter. Does this mean that a thing always moves in a straight line (apart from other externally-applied forces) but GR identifies the curvature of spacetime due to gravity as, essentially, the redefinition of what a straight line is? ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 26, 2025, 4:40pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2483 "2025-05-26T16:40:28Z")
Yes, that’s essentially correct. To avoid confusion, the term usually used is “geodesic” rather than “straight line”. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [May 26, 2025, 5:15pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2484 "2025-05-26T17:15:17Z")
Right. To extend that, a geodesic is the shortest possible line on a curved surface. That makes it the most energy efficient pathway and the natural way a massed body would move in space (without exterior forces). On the surface of a globe, the geodesic connects two points with the shortest travel distance. Airplanes normally travel along these routes, which is why so many routes cross arctic territories. And why flatearthers have to flatly deny that southern hemisphere flights exist. That sounds insane because it is, but no other out is available on a flat earth. ---
**Author:** ![pjd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pjd/32/3009_2.png) [@pjd](https://boards.straightdope.com/u/pjd)\ **Post date:** [May 26, 2025, 5:34pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2485 "2025-05-26T17:34:44Z")
> [@Frodo](#): > > Also the question did not clarify that the cities were on Earth That’s why the correct answer is c. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 26, 2025, 5:42pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2486 "2025-05-26T17:42:34Z")
> [@Whack-a-Mole](#): > > Einstein says otherwise. No experiment can distinguish between being in a gravitational field and/or experiencing uniform acceleration. See: [Equivalence Principle.](https://en.wikipedia.org/wiki/Equivalence_principle) > > Put another way…gravity _feels exactly_ like uniform acceleration. The two cannot be distinguished. You’ve got that exactly backwards. When you’re falling is when you’re not accelerating. It’s when something is stopping you from falling, like the floor or a chair, that you’re accelerating. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 6:50pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2487 "2025-05-26T18:50:33Z")
> [@Chronos](#): > > You’ve got that exactly backwards. When you’re falling is when you’re not accelerating. It’s when something is stopping you from falling, like the floor or a chair, that you’re accelerating. What? You can’t be serious. (bolding mine for emphasis) > Einstein’s first step towards that theory was the realization that, even in a gravitational field, there are [reference frames](https://www.einstein-online.info/en/explandict/reference-frame-1/) in which gravity is nearly absent; in consequence, physics is governed by the laws of gravity-free special relativity – at least to a certain approximation, and only if one confines any observations to a sufficiently small region of space and time. **This follows from what Einstein formulated as his _equivalence principle_ which, in turn, is inspired by the consequences of free fall.** - [SOURCE](https://www.einstein-online.info/en/spotlight/equivalence_principle/) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 26, 2025, 6:56pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2488 "2025-05-26T18:56:24Z")
Sit in a chair holding an accelerometer. The accelerometer reads 1 g. Jump out of a plane holding an accelerometer. The accelerometer reads 0. The equivalence principle is basically just the statement that the accelerometer is correct. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [May 26, 2025, 7:02pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2489 "2025-05-26T19:02:17Z")
My instinctive guess is that a “force” and a geometric explanation of acceleration should be inter-equivalent. We just haven’t come up with convincing geometric interpretations of the other three forces, and we haven’t come up with a consistent interpretation of gravity in terms of quantum force bosons. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 7:07pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2490 "2025-05-26T19:07:55Z")
ISTM that’s just two different reference frames. One where you “feel” gravity and one where you do not. The Equivalence Principle still applies in both though. You cannot do an experiment to determine whether you are in a gravitational field or are uniformly accelerating. Astronauts in the ISS do not “feel” gravity but the Equivalence Principle still applies to them (see my cite above). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 26, 2025, 7:10pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2491 "2025-05-26T19:10:27Z")
Yes, it applies to them. They feel nothing, therefore they are not accelerating. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 7:12pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2492 "2025-05-26T19:12:38Z")
> [@Chronos](#): > > They feel nothing, therefore they are not accelerating. What? They are in orbit. They are constantly accelerating. See: [Centripetal Acceleration](https://courses.lumenlearning.com/suny-physics/chapter/6-2-centripetal-acceleration/) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 26, 2025, 7:26pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2493 "2025-05-26T19:26:10Z")
OK, picture a spacecraft in the depths of one of the great intergalactic voids, with its engines off. We can agree that that spacecraft is not accelerating, right? Well, an astronaut in that spacecraft would feel the same thing, and make all the same measurements, as one in the ISS. If they’re making the same measurements, then they have the same acceleration. If an astronaut at the ISS were accelerating, their path would deviate away from a geodesic. But that only happens if there’s some real force acting on them. But there isn’t any real force, only gravity. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [May 26, 2025, 7:28pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2494 "2025-05-26T19:28:51Z")
> [@Whack-a-Mole](#): > > The Equivalence Principle still applies in both though. You cannot do an experiment to determine whether you are in a gravitational field or are uniformly accelerating. With the caveat of course that uniform acceleration corresponds to a gravity source infinitely far away i.e. no tidal forces. Or as you said “if one confines any observations to a sufficiently small region of space and time.” ---
**Author:** ![Slithy\_Tove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/slithy_tove/32/18248_2.png) [@Slithy\_Tove](https://boards.straightdope.com/u/Slithy_Tove)\ **Post date:** [May 26, 2025, 8:09pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2495 "2025-05-26T20:09:15Z")
Parachutists are subject to a form of this. They exit the aircraft being thrown forward by its momentum and don’t feel the drop. By the time this force is spent they’ve reached terminal velocity and don’t experience acceleration. Lacking visual reference they may become disoriented during the sensation of floating. This was the cause of the [1997 Antarctic parachute disaster.](https://www.southpolestation.com/trivia/90s/skydive.html) The participants who’d used Automatic Activation Devices, mostly Norwegians, survived. Norwegians seem to have the best outcomes at the South Pole ---
**Author:** ![Frodo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/frodo/32/302_2.png) [@Frodo](https://boards.straightdope.com/u/Frodo)\ **Post date:** [May 26, 2025, 8:11pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2496 "2025-05-26T20:11:22Z")
Except for that whole base that disappeared mysteriously in 1982… ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 8:50pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2497 "2025-05-26T20:50:39Z")
Are you suggesting the Equivalence Principle only applies in a few, particular circumstances? ---
**Author:** ![Treppenwitz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/treppenwitz/32/3445_2.png) [@Treppenwitz](https://boards.straightdope.com/u/Treppenwitz)\ **Post date:** [May 26, 2025, 8:56pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2498 "2025-05-26T20:56:14Z")
And in a shocking change of tone, I discovered yesterday that seminal rocker Little Richard was discovered by Sister Rosetta Tharpe. What?? I am incredulous that I didn’t know this. > Little Richard referred to her as his favorite singer when he was a child. In 1947, she heard Richard sing before her concert at the Macon City Auditorium and later invited him on stage to sing with her; it was Richard’s first public performance outside of the church. Following the show, she paid him for his performance, which inspired him to become a performer. Jeez, they even made an album together… > **[Little Richard & Sister Rosetta Tharpe | Smithsonian Institution](https://www.si.edu/object/little-richard-sister-rosetta-tharpe%3Anmaahc_2014.98.17ab)** (If you don’t know who Sister Rosetta Tharpe is, time to fight some ignorance.The Godmother of Rock And Roll. > **[Sister Rosetta Tharpe](https://en.wikipedia.org/wiki/Sister_Rosetta_Tharpe#)** > > Sister Rosetta Tharpe (born Rosetta Nubin, March 20, 1915 – October 9, 1973) was an American singer, songwriter and guitarist. She gained popularity in the 1930s and 1940s with her gospel recordings, characterized by a unique mixture of spiritual lyrics and electric guitar. She was the first great recording star of gospel music, and was among the first gospel musicians to appeal to rhythm-and-blues and rock-and-roll audiences, later being referred to as "the original soul sister" and "the Godm Was she good? Was she ever! [![](https://img.youtube.com/vi/jGPx4ancGhg/hqdefault.jpg "Sister Rosetta Tharpe - Didn't It Rain-Live In Manchester, England 1964") ](https://www.youtube.com/watch?v=jGPx4ancGhg) BTW the weather’s pretty typical for Manchester. That is all.) j ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 26, 2025, 9:13pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2499 "2025-05-26T21:13:57Z")
No, it applies in all circumstances. That’s why we can absolutely definitely say that objects in orbit aren’t accelerating. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 26, 2025, 9:20pm UTC](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2500 "2025-05-26T21:20:11Z")
> [@Chronos](#): > > That’s why we can absolutely definitely say that objects in orbit aren’t accelerating. See the [post above.](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785/2492) Everything in orbit is under constant acceleration. Maybe we are talking past each other. [Previous page](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785.md?page=124) [Next page](https://boards.straightdope.com/t/tell-us-an-interesting-random-fact-you-stumbled-across-part-2/1004785.md?page=126)