News:

Welcome to our site!

Main Menu

why are you an atheist?

Started by randomvim, September 11, 2016, 03:14:56 AM

Previous topic - Next topic

Baruch

Quote from: Cavebear on August 01, 2019, 08:54:28 AM
It's time.

When a body enters a planetary gravity, it speeds up.  So it is in the approach longer than the escape.  Therefore, more escape velocity.  As simple as that may seem, I never heard it explained.  And it bothered the hell out of me.  So one night, I just sat down an thought about it. 

I didn't get it while awake.  I went to bed.  And in the night (brain sorting out questions), it hit me like a wet mackerel to the cheek...

I woke up the next morning and understood what was happening in a flyby maneuver.  My one great conception.  (hey, no children jokes, OK)?

It has to do with gain and loss of kinetic energy.  More KE, more speed.
Ha’át’íísh baa naniná?
Azee’ Å,a’ish nanídį́į́h?
Táadoo ánít’iní.
What are you doing?
Are you taking any medications?
Don't do that.

Cavebear

Quote from: Baruch on August 01, 2019, 03:23:49 PM
It has to do with gain and loss of kinetic energy.  More KE, more speed.

I think spherical geometry.  I  don't know why.  I can just visualize it easily.
Atheist born, atheist bred.  And when I die, atheist dead!

josephpalazzo

Quote from: Cavebear on August 01, 2019, 08:54:28 AM
It's time.

When a body enters a planetary gravity, it speeds up.  So it is in the approach longer than the escape.  Therefore, more escape velocity.  As simple as that may seem, I never heard it explained.  And it bothered the hell out of me.  So one night, I just sat down an thought about it. 

I didn't get it while awake.  I went to bed.  And in the night (brain sorting out questions), it hit me like a wet mackerel to the cheek...

I woke up the next morning and understood what was happening in a flyby maneuver.  My one great conception.  (hey, no children jokes, OK)?

Sorry to rain on your parade, but that's not quite right. The reason the slingshot maneuver is effective it's that the body picks up energy from the rotation of the earth. Why it's also called gravity assisted - the rotation of the earth is effectively assisting the pull of gravity, both acting together to transfer energy to the body. Thus gaining more speed than when it entered into this maneuver. Hope this is clear... :-)

Baruch

Quote from: Cavebear on August 01, 2019, 03:47:11 PM
I think spherical geometry.  I  don't know why.  I can just visualize it easily.

Yes.  That must have a lot to do with it.  Never was very good getting out of the Orthonormal Cartesian system.
Ha’át’íísh baa naniná?
Azee’ Å,a’ish nanídį́į́h?
Táadoo ánít’iní.
What are you doing?
Are you taking any medications?
Don't do that.

aileron

I'm an atheist because a surfeit of data and powerfully-confirmed theories lead us to conclude "God did it" is a failed hypothesis. I see no reason whatsoever to exclude from scientific inquiry the existence or non-existence of supernatural forces.
Gentlemen, you can't fight in here! This is the War Room! -- President Merkin Muffley

My mom was a religious fundamentalist. Plus, she didn't have a mouth. It's an unusual combination. -- Bender Bending Rodriguez

Cavebear

Quote from: josephpalazzo on August 01, 2019, 10:07:12 PM
Sorry to rain on your parade, but that's not quite right. The reason the slingshot maneuver is effective it's that the body picks up energy from the rotation of the earth. Why it's also called gravity assisted - the rotation of the earth is effectively assisting the pull of gravity, both acting together to transfer energy to the body. Thus gaining more speed than when it entered into this maneuver. Hope this is clear... :-)

Wasn't describing Earth orbits.  I was describing non-orbital approaches to and from other planets.  Though it IS accurate for Earth fly-bys from non-orbital approaches...
Atheist born, atheist bred.  And when I die, atheist dead!

Baruch

Quote from: Cavebear on August 05, 2019, 12:01:09 PM
Wasn't describing Earth orbits.  I was describing non-orbital approaches to and from other planets.  Though it IS accurate for Earth fly-bys from non-orbital approaches...

It is all conics, you cone head!
Ha’át’íísh baa naniná?
Azee’ Å,a’ish nanídį́į́h?
Táadoo ánít’iní.
What are you doing?
Are you taking any medications?
Don't do that.

josephpalazzo

Quote from: Cavebear on August 05, 2019, 12:01:09 PM
Wasn't describing Earth orbits.  I was describing non-orbital approaches to and from other planets.  Though it IS accurate for Earth fly-bys from non-orbital approaches...

Maybe my mistake, but your question was: "Have you ever wondered WHY spaceship slingshot pass-bys increase speed?" The slingshot usually occurs around whether it's the earth or any other object like the moon or the sun. I don't know what non-orbital means. In the solar system, you are going to orbit something... unless you have enough energy to escape Helios and go where no man has gone before...

Cavebear

Quote from: josephpalazzo on August 06, 2019, 05:00:04 PM
Maybe my mistake, but your question was: "Have you ever wondered WHY spaceship slingshot pass-bys increase speed?" The slingshot usually occurs around whether it's the earth or any other object like the moon or the sun. I don't know what non-orbital means. In the solar system, you are going to orbit something... unless you have enough energy to escape Helios and go where no man has gone before...

I have to rethink the explanation.  So a ship goes around a Jupiter flyby to gain speed.  Why does it gain speed?  After all, the gravity pull should equal it towards and from Jupiter.  What is gained should be equally lost.

Now picture the fly-by in 2 equal parts of distance.  Half coming to the nearest approach and half exiting.  On approach, the spaceship is travelling X miles per hour.  So it is in the approach for a certain length of time and Jupiter's gravity acts on it then.  The spaceship gains velocity.

On the exit half, the spaceship is still in Jupiter's gravity but not for as long because it is moving faster.  And gravity is about time.  So when the spaceship is exiting the half of the flyby, it is affected by Jupiter's gravity for less time.  So it exits with a speed gain.

And technically, Jupiter looses that same amount of speed.  It's infitesimal but real. 

But the spaceship was approaching the closest approach (gravity well) longer then it took to exit.  Wikipedia says "Important parameters are the time and distance of closest approach".

I did see something about benefits from the direction of planetary rotation, but I'm pretty sure flybys don't depend on that.

What am I getting wrong?
Atheist born, atheist bred.  And when I die, atheist dead!

josephpalazzo

Quote from: Cavebear on August 08, 2019, 12:29:00 PM
I have to rethink the explanation.  So a ship goes around a Jupiter flyby to gain speed.  Why does it gain speed?  After all, the gravity pull should equal it towards and from Jupiter.  What is gained should be equally lost.

Now picture the fly-by in 2 equal parts of distance.  Half coming to the nearest approach and half exiting.  On approach, the spaceship is travelling X miles per hour.  So it is in the approach for a certain length of time and Jupiter's gravity acts on it then.  The spaceship gains velocity.

On the exit half, the spaceship is still in Jupiter's gravity but not for as long because it is moving faster.  And gravity is about time.  So when the spaceship is exiting the half of the flyby, it is affected by Jupiter's gravity for less time.  So it exits with a speed gain.

And technically, Jupiter looses that same amount of speed.  It's infitesimal but real. 

But the spaceship was approaching the closest approach (gravity well) longer then it took to exit.  Wikipedia says "Important parameters are the time and distance of closest approach".

I did see something about benefits from the direction of planetary rotation, but I'm pretty sure flybys don't depend on that.

What am I getting wrong?

It's well known as gravity assisted - The object flying by gets rotational energy from the planet. It's that simple. You can only reason this by looking at energy, since this is a conserved quantity. So the object cannot get more speed, that is more kinetic energy, it must get it from somewhere else. In this case it's not gravity, which would balance out (KE before = KE after), and so there would be no slingshot effect.

Cavebear

Quote from: josephpalazzo on August 08, 2019, 12:58:25 PM
It's well known as gravity assisted - The object flying by gets rotational energy from the planet. It's that simple. You can only reason this by looking at energy, since this is a conserved quantity. So the object cannot get more speed, that is more kinetic energy, it must get it from somewhere else. In this case it's not gravity, which would balance out (KE before = KE after), and so there would be no slingshot effect.

So you are saying a flyby has to be in the direction of planetary rotation?
Atheist born, atheist bred.  And when I die, atheist dead!

josephpalazzo

Quote from: Cavebear on August 08, 2019, 01:38:01 PM
So you are saying a flyby has to be in the direction of planetary rotation?

Of course. If you go opposite, you'll speed down and the planet will absorb energy. This happens frequently with the earth as comets, asteroids, meteorites and other debris fly by. But over millions of years, these effects cancel out. The other things that don't cancel:  from our atmosphere, as the earth rotates, air molecules are thrown off the planet, reducing the rotation of the earth; there is also a transfer of rotational energy to the moon. There are also other factors not well-known  like earthquakes, but the earth is slowing down, some 2.3 milliseconds per century.

Cavebear

Quote from: josephpalazzo on August 08, 2019, 01:58:45 PM
Of course.

Damn!  I never realized the flybys (to increase velocity) had to go with the rotational direction of the gravity well.

No one ever tells me these things (well, yeah you did, thank you).  And here I thought I finally understood some minor thing about gravity and time...

I think I should just buy 100 cases of wine, sit in my chair, and play Civ2 until someone comes by to dispose of my body and rescue the cats...
Atheist born, atheist bred.  And when I die, atheist dead!

Sal1981

My gymnasium final project was in that in physics. I got what amounts to a C in grades :/ because I effed up the gravitational slingshot equations for it. We didn't have google back then.

https://en.wikipedia.org/wiki/Gravity_assist

josephpalazzo

Quote from: Cavebear on August 08, 2019, 02:13:20 PM
Damn!  I never realized the flybys (to increase velocity) had to go with the rotational direction of the gravity well.

No one ever tells me these things (well, yeah you did, thank you).  And here I thought I finally understood some minor thing about gravity and time...

I think I should just buy 100 cases of wine, sit in my chair, and play Civ2 until someone comes by to dispose of my body and rescue the cats...

Slight correction: rotation direction of the planet, not gravity... Civ2, that still exists??