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Message 2070308 - Posted: 10 Mar 2021, 8:09:46 UTC - in response to Message 2070307.

No, the forward momentum of the satellite is the stronger force, with gravity as the weaker force causing it to drop slightly...

The earth's gravity, for our example, acts to change the direction of travel of the satellite. Otherwise, the satellite would continue onwards on a straight line path and would no longer be a satellite.

Note that the 'change in direction' is the act of the satellite enjoying a freefall acceleration towards the earth.

As Douglas Adams beautifully explains, the trick is to enjoy that freefall but to always miss the ground...

A satellite always misses the ground due to enjoying enough orbital velocity such that as it accelerates towards the earth, it has enough perpendicular orbital motion such that the earth always remains perpendicular to that orbital motion despite the continual freefall acceleration towards the earth.

This all works beautifully for a round sphere for the earth.

A flat earth would be somewhat problematic for orbits!
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Message 2070311 - Posted: 10 Mar 2021, 11:21:15 UTC - in response to Message 2070308.

No, the forward momentum of the satellite is the stronger force, with gravity as the weaker force causing it to drop slightly...

The earth's gravity, for our example, acts to change the direction of travel of the satellite. Otherwise, the satellite would continue onwards on a straight line path and would no longer be a satellite.

Note that the 'change in direction' is the act of the satellite enjoying a freefall acceleration towards the earth.

As Douglas Adams beautifully explains, the trick is to enjoy that freefall but to always miss the ground...

A satellite always misses the ground due to enjoying enough orbital velocity such that as it accelerates towards the earth, it has enough perpendicular orbital motion such that the earth always remains perpendicular to that orbital motion despite the continual freefall acceleration towards the earth.

This all works beautifully for a round sphere for the earth.

A flat earth would be somewhat problematic for orbits!

International Space Station, only 420km above Earth, where people are weightless, because gravity is so weak,
Forward motion - 27,600 km/h
Downward motion - 2 km/month
ID: 2070311 ·
rob smith
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Message 2070312 - Posted: 10 Mar 2021, 11:58:32 UTC - in response to Message 2070311.

Well, yes and no.
The tangential velocity component of the space station is such that the vertical component of its free-fall and so it is pulled into, what appears to us to be a circular orbit. Think of spinning a ball on a string around one's head - the string is "gravity", the ball the space station, and one's head is the earth. At any instant the ball is moving tangential to the described circle, but the ball is pulled by the string to describe an arc; stop spinning the ball around and it stops following that arc... Not a prefect analogy, but a fair starter for ten.
The station is subject to drag (yes, even up there, drag!!) which causes it to slow down a tiny bit, and so loose ~2k per month and it has to be sped up a tiny bit every now and then to compensate.
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Message 2070313 - Posted: 10 Mar 2021, 12:34:18 UTC - in response to Message 2070312.

I agree that the loss of height is due mainly to loss of momentum rather than the pull of gravity.

Which leads me to one of my favourite quiz questions. What objects do you speed up to move them backwards and slow down to move them forward?
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Carlos
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Message 2070314 - Posted: 10 Mar 2021, 13:14:06 UTC - in response to Message 2070313.

Speeding up puts orbiting objects into a higher, longer orbit. Relative velocity is thus decreased because of the greater distance to cover. Slowing down brings them down into a shorter orbit. So that relative velocity increases due to the short cut. So the answer must be the grease gun dropped in space Nov 18, 2008
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Message 2070323 - Posted: 10 Mar 2021, 13:38:05 UTC - in response to Message 2070311.

International Space Station, only 420km above Earth, where people are weightless, because gravity is so weak...

Ooooooer!

I think you'll find that "up there" you'll still have most of our earthly freefall acceleration of 9.8 metres per second per second. Compared to the radius of the earth, 'up there' ain't very far away.

Hence. do a Blue Origin and rocket straight up there (zero orbital velocity) and you come straight back down falling such that you accelerate towards the ground at that 9.8m/s2. The joyriders enjoy the thrill of 'weightlessness' as they too plummet back to the ground at the same increasing speed as does the capsule around them. Until that is eventually air resistance slows the capsule and the joyriders gently bump into the lower end to start to 'feel' ever more of their 'weight' again as the capsule slows down.

In the ISS, the astronauts feel themselves to be weightless due to being in freefall. They just happen to be falling in formation with the rest of the ISS.

Now for the clever bit:

To fall around the earth (to be in an orbit), you contrive the orbital velocity to be such that a change in velocity (note that velocity is speed along a direction = momentum) of freefall towards the earth (9.8 m/s2) nicely gives you exactly the right 'delta-v' to always turn your direction to guide you around the earth.

(Your angular momentum remains constant, whereas the directional moment is constantly changing direction so as to continue to point along the orbit.)

And then there is the game of conservation of energy for going slower so as to then speed up again when then falling down into stabilizing in a lower orbit...

Edit: Didn't anyone tell the Blue Origin Marketing Team that "blue" usually indicates that the passengers are suffering a lack of oxygen?
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Carlos
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Message 2070337 - Posted: 10 Mar 2021, 15:57:47 UTC

Thanatos, in ancient Greek religion and mythology, the personification of death. ... Thanatos was the son of Nyx, the goddess of night, and the brother of Hypnos, the god of sleep. He appeared to humans to carry them off to the underworld when the time allotted to them by the Fates had expired.
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Message 2070369 - Posted: 10 Mar 2021, 20:59:45 UTC

As we know what goes up must come down. The trick is keeping it up. I thought you could use a few more orbital mechanics numbers.

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Message 2070378 - Posted: 10 Mar 2021, 22:34:33 UTC - in response to Message 2070369.

Thanks for that. Very good!
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kittyman
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Message 2070749 - Posted: 15 Mar 2021, 11:51:09 UTC

Jesus-----terrorist?
WTF???
"Freedom is just Chaos, with better lighting." Alan Dean Foster

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Message 2070752 - Posted: 15 Mar 2021, 12:04:21 UTC - in response to Message 2070749.

Jesus-----terrorist?

That all depends on whether you side with which of:

• King Herod
• The People's Liberation Front of Judea
• The Pharisee(sp?)
• Pontius Pilot
• A Goatherder
• A Carpenter

Keep searchin',
Martin

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Message 2070754 - Posted: 15 Mar 2021, 12:10:14 UTC - in response to Message 2070749.

Jesus-----terrorist?
WTF???

He, and some of his followers, attended a training camp run by John the Baptist, who was executed for his crimes, in AD 28 or 29.
He hung out with known terrorists like Simon the Zealot. The Zealots would later go on to stab Romans and Roman sympathisers.
He vandalised the Temple and smashed up traders tables. John 2:13 onwards
He said the Temple would soon be destroyed. Mark 13:2
He said, “I did not come to bring peace, but a sword” (Matthew 10:34)

And if alive today would not get permission to enter the U.S.
ID: 2070754 ·
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Message 2070869 - Posted: 16 Mar 2021, 22:27:40 UTC

Shocked.
No responses.
ID: 2070869 ·
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Message 2070871 - Posted: 16 Mar 2021, 22:29:56 UTC - in response to Message 2070869.

Alleluia?
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Carlos
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Message 2070932 - Posted: 17 Mar 2021, 14:32:04 UTC

In my teen years BASF was synonymous with cassettes. I don't know if Memorex out sold them but BASF was considered, in my circle, the gold standard.
History of BASF Cassettes.
ID: 2070932 ·
kittyman
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Message 2070933 - Posted: 17 Mar 2021, 14:39:25 UTC - in response to Message 2070932.

Oh yeah.
I sold a ton of BASF cassette and video tape when I worked at a high end audio dealer when I was in my 20's.
Many kitty moons ago....LOL.
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kittyman
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Message 2070936 - Posted: 17 Mar 2021, 14:56:24 UTC

A very iconic piece of history, actually.
The music video for Video Killed the Radio Star was the very first video that launched MTV.
Remember when?
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W-K 666
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Message 2070938 - Posted: 17 Mar 2021, 15:20:18 UTC - in response to Message 2070936.

Sequence completed.
ID: 2070938 ·
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Message 2070967 - Posted: 17 Mar 2021, 17:53:47 UTC

https://en.wikipedia.org/wiki/Tokamak
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rob smith
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Message 2071156 - Posted: 19 Mar 2021, 9:04:05 UTC

Recently there have been a few entries that do not have a link to the last post, but to one further back in history.
This can happen when two respond within a short time of each other (say a couple of minutes), which is fair enough. However some have been tens of minutes "late". If you find your post is very late, and doesn't link to the current last word then either hit the red-x, or (preferred) edit your post with a new word - either of these actions will save your bar bill in Rocky's, or a moderator hiding your word (which in this game can cause lots of "fun" and is very much a last resort).
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