## How does gravity work? II

How does science work? And what's all this about quantum mechanics?

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thedoc
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### Re: How does gravity work? II

Noax wrote:I heard that the crown was found to be pure gold, and no execution. Same story, but different ending. Was I told the story wrong? Too PC of a school to describe an execution, but it was OK to give us an image of Archimedes running naked down the road?

The balloon in the car thing is also buoyancy. It is an illustration of one of the initial thought experiments for general relativity. Einstein stated that there was no local experiment that could differentiate gravity from acceleration. Hence, a sealed/soundproofed car with the windows painted black and the balloon coming to the windshield: Is the car accelerating or it just parked pointing uphill? Einstein said you can't tell the difference.
If the version you heard had Archimedes finding the crown to be pure gold, then there are at least 2 versions of the story being told, but I have never heard that the crown was found to be pure gold. Just curious, where and when did you hear that version?

Yes, I wanted to include buoyancy as one of the factors in the movement of the balloon, but I couldn't remember it when I wrote the post. Thankyou. Yes I know it's mentioned in the post right before mine, just a bit of brain fade, it happens when you get old.

Noax
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### Re: How does gravity work? II

thedoc wrote:If the version you heard had Archimedes finding the crown to be pure gold, then there are at least 2 versions of the story being told, but I have never heard that the crown was found to be pure gold. Just curious, where and when did you hear that version?
I recall it from a specific history teacher when I was about 14. Funny that I remember who told it. Who the heck knows how sound that memory is.

The method used was to get a brick of gold the same weight as the crown, and immerse that brick in water so the water spilled from the full container. Carefully (no waves) remove the brick and replace with the crown, which should bring the water back up exactly to the top. If water level is lower, the crown has something heavier than gold in it (few materials are heavier), and if any additional water spills, the crown has a lighter impurity. No buoyancy involved. That's how the story was told to me, and I recall being told that the crown passed the test, but I could well be wrong about that.
Yes, I wanted to include buoyancy as one of the factors in the movement of the balloon, but I couldn't remember it when I wrote the post. Thankyou. Yes I know it's mentioned in the post right before mine, just a bit of brain fade, it happens when you get old.
Been there, doing that. Been an awful long time since I was 14.

thedoc
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### Re: How does gravity work? II

Noax wrote:Been there, doing that. Been an awful long time since I was 14.
What bothers me most is when you tell someone something that you have done and they argue with you, saying you couldn't have done it. I made a Nativity candle stand for our church and presented it to the church many years ago, then in 2010 our church burned but the candle stand was saved, it needed a bit of cleaning but it was otherwise OK. Then in 2012 we moved into the new building for the church and when I tried to tell people that I had made the candle stand and it belonged to our congregation, they argued with me claiming that my memory must be wrong.

Noax
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### Re: How does gravity work? II

thedoc wrote:
Noax wrote:Been there, doing that. Been an awful long time since I was 14.
What bothers me most is when you tell someone something that you have done and they argue with you, saying you couldn't have done it. I made a Nativity candle stand for our church and presented it to the church many years ago, then in 2010 our church burned but the candle stand was saved, it needed a bit of cleaning but it was otherwise OK. Then in 2012 we moved into the new building for the church and when I tried to tell people that I had made the candle stand and it belonged to our congregation, they argued with me claiming that my memory must be wrong.
Harsh...

True or False: Noax sings in his Church choir.

thedoc
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### Re: How does gravity work? II

Noax wrote: True or False: Noax sings in his Church choir.
I would hope that you do, I would but I don't have the breath to last for any length of time, due to CHF. Many years ago my wife and I were both in a church choir and the director got the idea that we would sing together better if we knew each other better. So she started asking us to name our favorites, food, TV show, etc. finally it got around to color and I was getting tired of the game. She started with the sopranos and I was in the bass section so I was close to the end, and everyone was giving the typical answer of red, blue, green, etc. It finally got to me and I said my favorite color was 'flesh'. The whole group broke up with laughter and the director decided that we should just get back to singing.

attofishpi
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### Re: How does gravity work? II

Noax wrote:True or False: Noax sings in his Church choir.
It's interesting that you would be in a church choir. Perhaps more interesting is that you might not be singing while in the choir.

Dubious
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### Re: How does gravity work? II

uwot wrote:
thedoc wrote:I made the condition of a closed car with the assumption that no air would be escaping. In a car that is moving at a steady speed no air is moving inside the car, as it is all moving along with the car, just as the atmosphere is moving with the Earth as it orbits the Sun and spins on it's axis. When the car accelerates the inertia of the air moves it to the back of the cabin raising the pressure there and lowering it toward the front, thus the balloon moves toward the lower air pressure, and the opposite occurs during braking. So the movement is due to inertia, and air pressure, the assumption is that no air is escaping or entering the cabin.
Makes sense. Thank you, I've learnt something new.