More Science

[Homer]

Okay, I have a couple of questions now, about science, and layman's answers would be appreciated.

1) OK, its a given that the more mass an object has the more gravitational pull it has. When one stands on a planet, that planets grvity pulls on the mass of the person, and the result is registered as weight. Here is my question, shouldn't a planets mass affect nearby objects? For example, a ship nears a planet that masses three times the Earth. (For this example the ship has no artificial gravity). If it were to land a 100 kg man from Earth would feel he weighed 300kg, as the pull is three times as strong.

Shouldn't the ship pass through a zone where everyone feels 1g, the 2g, and so on until they landed? I have been told NO by some sources, but logic dictates, that not increasing gravity as one closes, makes no sense.

As a side note, this guy, our Mr. Science says it is the one thing they got right in the Black Hole the movie, as the Palomino is being drawn in the opening sequence, the gravity is sucking in the ship the the crew is in zero g inside. Shouldn't they be drawn toward the bulkhead nearest the source of the gravity well? Especially if it is dozens of g's??

This other one is tougher. We know stars die. When they die they expel matter into the void creating nebulae. Much of this matter forms planets and new stars. I was watching a show saying the universe will die a cold and dark place with little or no light, and not transfer of heat. Why would this happen? Wouldn't star formation continue ad infinitum? Or relatively there of? I mean the show said that as stars die nothing will replace them. BUT we know that a single star death can generate several new stars, just using the Pleiadies as an example, many stars coming out of a single nebula. Why would this NOT be true of the future, and why does an expanding universe exaggerate the calims? BTW, we are talking about a documentary called Universe 2000 (I think), from TLC, not SF. Has anyone else heard of this and know what the completet theory is, and can you explain it in layman's terms?

I hope to use the data in future games, but I nedd more info.

[Phantom]

I think I saw the show you are talking about. I'm not sure that I understand anymore of it then you do...no hard science background here.

About the second part of your question, wouldn't the universe "eventually" run out of the material to make stars after having done so over X billions of years? Some, please, correct me if I am wrong, but I think that was the idea they were trying to convey.

Unfortunatly, my group is no longer around...Two of my buddies, who know way more the subject then I ever will, figured out the backward acceleration caused when a Shiva-class battleship fired its spinal mount from a stand still. Yeah, what can I say. They had alot of time on thier hands that day I guess. Anyway, they have tried to tell me about gravity phenomena...Way too deep for me.

[Robert Lai]

Okay, my physics class was long ago, but here goes ...

Although larger masses exert stronger fields, their gravitational pull is governed by an inverse proportion ... so that while the sun is far more massive than you or I, if we're standing side-by-side, I have a stronger gravitational influence on you than the sun does.
(This is often used by skeptics to make light of astrology, i.e. the obstetrician taking you from the womb has a greater pull on you than Mars or Jupiter.)

I believe that curve is not a linear one, i.e. 10,000 feet up isn't automatically 1/10 off the planet's gravitational pull, and so on. So the 'zones' you were postulating are likely so small as to be unnoticeable unless you're hovering at a fixed altitude.

As for the 'never-ending' universe, you're caught in one of the great debates of cosmic theory: is the universe steady-state (i.e. stars die, raw materials recombine to form new stars, life goes on) or finite (stars die, there is LESS material from which new stars can form, and eventually the universe will go dark). Arguments can be made in either direction.

How can there be less material? Stars burn by fusion, with lighter elements becoming heavier ones (from hydrogen to iron, mostly) ... so when they end their lives, there will be less material likely to form a new star.

What you are seeing in the Pleiades is not necessarily the rebirth of stars from older material, but newborn stars that have not yet burned off the wispy clouds of hydrogen left from their formation.

Hope that helps.

Bob

[Imagus]

Originally posted by Homer
Okay, I have a couple of questions now, about science, and layman's answers would be appreciated.

1) OK, its a given that the more mass an object has the more gravitational pull it has. When one stands on a planet, that planets grvity pulls on the mass of the person, and the result is registered as weight. Here is my question, shouldn't a planets mass affect nearby objects? For example, a ship nears a planet that masses three times the Earth. (For this example the ship has no artificial gravity). If it were to land a 100 kg man from Earth would feel he weighed 300kg, as the pull is three times as strong.

Yep!

Shouldn't the ship pass through a zone where everyone feels 1g, the 2g, and so on until they landed? I have been told NO by some sources, but logic dictates, that not increasing gravity as one closes, makes no sense.

Ok, nice easy one to start with!

This is and is not the case! As long as it's not actually using its engines, the ship and everything inside it are in freefall - what this means is that the gravity is affecting everything equally. The ship is being affected by the gravity causing it to accelerate toward the planet at the relevant rate (approx 10 m/s/s on Earth), and so are the inhabitants. The entire environment is affected the same way so no one feels anything.

The trick of freefall flights on aircraft, where the the plane dives straight downwards to generate weightlessness relies on this. A skydiver also feels no pull as he falls.

If the ship is trying to stay up by using its engines, then the inhabitants will fall towards the surface closest to the planet and then will feel "weight" which is actually the surface of the ship holding him up. A planet's surface does the same job.

Incidentally, in a stable orbit, the ship is falling "past" the planet, being constantly pulled acrosstowards it, but never quite enough to hit it. Hence in orbit, a ship is in freefall.

Straight answer - yes the ship feels the gravity increase, but since it's reaction is to fall faster, along with everybody on board, nobody can tell.

As a side note, this guy, our Mr. Science says it is the one thing they got right in the Black Hole the movie, as the Palomino is being drawn in the opening sequence, the gravity is sucking in the ship the the crew is in zero g inside. Shouldn't they be drawn toward the bulkhead nearest the source of the gravity well? Especially if it is dozens of g's??

Your mate is spot on - the Black Hole also got the ship stretching right as well (as did Space Above and Beyond). Close to a black hole, the gravity varies drastically over a matter of feet. If you were to fall feet downwards into one, your feet would be pulled harder than your head, and as Stephen Hawking might put it, you're looking at human spaghetti...

On this note, Robert is almost right - gravitational strength follows an inverse square law, like light. Double your distance (from the centre of the planet, not the surface), and quarter the strength.

This other one is tougher. We know stars die. When they die they expel matter into the void creating nebulae. Much of this matter forms planets and new stars. I was watching a show saying the universe will die a cold and dark place with little or no light, and not transfer of heat. Why would this happen? Wouldn't star formation continue ad infinitum? Or relatively there of? I mean the show said that as stars die nothing will replace them. BUT we know that a single star death can generate several new stars, just using the Pleiadies as an example, many stars coming out of a single nebula. Why would this NOT be true of the future, and why does an expanding universe exaggerate the calims? BTW, we are talking about a documentary called Universe 2000 (I think), from TLC, not SF. Has anyone else heard of this and know what the completet theory is, and can you explain it in layman's terms?

I think the general consensus these days runs like this.

Einstein's relativity states that energy and matter are interchangeable (the basic point of the notorious e=mc2). The total amount of matter/energy in the universe was fixed at the big bang. You can take it one way or the other, but you can neither create nor destroy it outright.

To create a new star the material and energy has to come from somewhere, and when it dies, that material goes somewhere. Where it comes from is other stars.

However, a lot of matter and energy from dying stars disappears into dead-end careers. Energy gradually spreads as far as it can - this is called entropy, and ultimately, all the universe will be the same temperature. Matter regularly ends up clumped with other matter - and large chunks land in black holes - once that happens it's completely useless.

Basically, the most likely future for the universe is heat death. The universe gets bigger, more energy disipates out into it to fill the gaps and entropy takes over. You get a lot of dead matter sitting in a single very low temperature environment (certainly too cold to sustain any further creation).

Of course, there is the big crunch to worry about. If the amount of matter in the universe is over a certain value gravity will slam everything back together in a reverse of the big bang. I think that is largely proved unlikely now though.

I hope to use the data in future games, but I nedd more info.

I hope this helps - please ask if you need more clarification.

[calguard66]

The reason you feel weight on earth is because you're in contact with the surface. If you weren't in contact, like skydiving you wouldn't feel the weight... just like those pictures you see of the astronauts training for zero-g in an aircraft in a long dive. They are within the atmosphere, but still weightless because they are falling.

The reason you don't feel weight in space is because everything in space is falling...

In orbit you're falling, but forward momentum keeps you missing the planet, so you just keep falling around it instead.

Everything in space is affected by gravity, and everything is in orbit around something else. A spaceship travelling from Earth to Mars is in orbit around the Sun... affected by gravity, but you don't notice because the spaceship is falling just as fast as you are... as if you were in a runaway elevator, floating in the center as it fell. You don't feel gravity until you come in contact with the source of the attraction... in this case, the bottom of the elevator shaft.

[Sarge]

Zero G training in airplanes is done when the airplane is following a roughly parabolic curve, starting at a steep upward angle and tilting gradually forward to level flight and continuing to lower the nose into a dive. It's not possible for most airplanes to dive toward the ground and accelerate straight down at one G long enough to do any zero G training before the wings rip off from the excessive airspeed.

The parabolic curve, OTOH, is such a simple maneuver that I've done it myself in Cessnas and Pipers.

[spyone]

I'll be as helpful as I can, which I think is a lot.

Originally posted by Homer
Okay, I have a couple of questions now, about science, and layman's answers would be appreciated.

1(snip)
Shouldn't the ship pass through a zone where everyone feels 1g, the 2g, and so on until they landed?

Yes and no.
Since gravity is a function of mass and distance, there is a distance from the planet where the force of gravity is 1 g.
However, see below:

As a side note, this guy, our Mr. Science says it is the one thing they got right in the Black Hole the movie, as the Palomino is being drawn in the opening sequence, the gravity is sucking in the ship the the crew is in zero g inside. Shouldn't they be drawn toward the bulkhead nearest the source of the gravity well? Especially if it is dozens of g's??

Not if the ship is falling too. While the people are being draw towards the center of the gravity well (a phenomenon known as "falling" ), so is the ship, and the wall of the ship is falling away at the same speed that the people are falling.
This is how NASA simulates zero-g in an airplane: it dives towards the earth at the same rate as falling, and the people inside float. Which lets you film the movie Apollo 13 if nothing else.

But, if the ship uses engines to slow down, the people go splat against a wall.

This is the exact same phenomenon often called "centrifugal force". When your car turns left, you feel as if you are being pulled to the right. The physics of what's happening, though, are that you are trying to continue straight (due to Newton's Third Law), and the car is moving into your path. It isn't that you are being pressed into the passenger-side door, it's that the door is moving into your way.

This other one is tougher. We know stars die. When they die they expel matter into the void creating nebulae. Much of this matter forms planets and new stars. I was watching a show saying the universe will die a cold and dark place with little or no light, and not transfer of heat. Why would this happen? Wouldn't star formation continue ad infinitum?

First, it is important to remember that matter and energy are the same thing. One can be turned into the other, and this is part of what goes on in stars.

Why will we eventually reach what is officially called the Heat-Death of the universe?
Well, the Third Law of Thremodynamics says that any time energy is transformed, like from heat to motion, some of it "escapes the system". This means, every time energy is used to do anything, some of the energy is lost. If I take 1 unit of heat and use it to produce motion, I get slightly less that 1 unit of kninetic energy (movement). REALLY slightly less, like 0.999999999999999...
Where does the energy go? Somewhere else.

"Escapes the system" means that the energy leaves the thing you are watching. For instance, some of the energy that drives your car is wasted doing other things. Ignoring the inefficency of the engine, the tires are experiencing friction, which is making them warm, so some of that energy is making warm tires instead of motion. The more factors you keep track of, the more energy you account for, but some of it always escapes.

If you are watching everything, the universe is your system. Every time energy is tranformed, some of it escapes the system. So, every time a star explodes, some of the energy is mass flying through space, and some of the energy is used to throw that mass, and some is a bright flash of light, and some is ...... and some of it leaves the universe. A very small amount, but some.

So, if you repeat that process enough times, eventually all the energy will have left.

Actually, to get rid of ALL the energy would require an infinite number of repetitions, but ...... Like the thing where each second you move halfway to the wall and never actually get there, at some point you are close enough to the wall that no one cares about the distance.
And, eventually there will be so little energy left in the universe that no one will care that it isn't all gone.