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Online Comics => Escape From Terra => Topic started by: Jtuxyan on August 03, 2009, 02:15:34 pm

Title: Physics Does Not Work that Way [Falling Assasin]
Post by: Jtuxyan on August 03, 2009, 02:15:34 pm
Gravity decreases with the square of the distance, regardless of source. So if this planet had 60% earth gravity at the surface, it will have 60% equivalent earth gravity at any altitude (IE, at say, 10,000ft, it will have 60% of 10,000ft gravity on earth). So in theory, the assassin should already realize how well and truly screwed he is.

Then again, this is all clearly a setup for something. Put me down for Tobi saving him.  ;)
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 03, 2009, 04:25:27 pm
Gravity decreases with the square of the distance, regardless of source. So if this planet had 60% earth gravity at the surface, it will have 60% equivalent earth gravity at any altitude (IE, at say, 10,000ft, it will have 60% of 10,000ft gravity on earth). So in theory, the assassin should already realize how well and truly screwed he is.

Very good pickup, but you forgot to factor in TLP's rotation (and the rotation of the atmo and airskin). The berg was put in an equatorial orbit so that it could be slowly transfered to a closer orbit in contact with the airskin to be "milked". When the pale man landed on the airskin, he did so near the equator. The airskin and Damocles Station are in synchronous orbit above TLP. So along the equator, TLP's gravity is matched by the centrifugal force of its rotation. Hence, there is only micro-gravity in the vicinity of the equatorial airskin.

Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Jtuxyan on August 03, 2009, 04:28:43 pm
Very reasonable! Though, the assassin still should have been able to figure out that microgravity corresponded to significant surface gravity.

Then again, he obviously isn't the brightest assassin in the night sky.  ::)
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 03, 2009, 06:46:44 pm
Very reasonable! Though, the assassin still should have been able to figure out that microgravity corresponded to significant surface gravity.

Then again, he obviously isn't the brightest assassin in the night sky.  ::)

Or even the brightest meteor!

Actually, some clues as to his perceptions were given as he alit. Like most people he only has a limited understanding of how things work. The transport pod was highly automated and just dealt with the conditions as they were, not as the Pale Man might have assumed. See strip 218.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Azure Priest on August 04, 2009, 03:15:45 am
Bwahahaha! Unless he lands right on them, he will surely fail in his mission. Even IF he lands on them and that kills his target, he's certainly not going to walk away from this one. SPLAT! And unless, this genius has some kind of anti-grav device, (he already mentioned that he didn't) I don't see him being able to sufficiently slow the assassin's descent in any manner that won't result in deceleration trauma.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: hans_meier on August 04, 2009, 09:18:42 am
It's not the fall that gets you.....it's the sudden stop at the end.........that's going to leave a mark.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Brugle on August 04, 2009, 06:55:42 pm
Gravity decreases with the square of the distance, regardless of source. So if this planet had 60% earth gravity at the surface, it will have 60% equivalent earth gravity at any altitude (IE, at say, 10,000ft, it will have 60% of 10,000ft gravity on earth). So in theory, the assassin should already realize how well and truly screwed he is.

Then again, this is all clearly a setup for something. Put me down for Tobi saving him.  ;)

With reasonable assumptions, gravity varies as the square of the distance from the center.  10000ft is tiny compared to the earth's radius, so gravity at 10000ft above the earth's surface is almost the same as at the surface.  10000ft is a significant fraction of TLP's radius, so gravity at 10000ft above TLP's surface is much less than at the surface.

Initially I thought that Tobi would save him, but what for?  He's unlikely to know anything useful.  (Of course, Tobi may enjoy saving lives.)
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: quadibloc on August 04, 2009, 08:23:02 pm
Actually, some clues as to his perceptions were given as he alit. Like most people he only has a limited understanding of how things work. The transport pod was highly automated and just dealt with the conditions as they were, not as the Pale Man might have assumed. See strip 218.

This makes sense as a way to deal with what is a vaild objection: that the orbital parameters of his ship should have tipped him off.

But then, our pair enjoying refreshments with the planetoid's owner were also surprised by the gravity later than they should have been... so being highly automated is apparently common in this future.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Sean Roach on August 04, 2009, 10:24:29 pm
Well.  It's probably the first planet they've been on with a functioning beanstalk.
Also, in 201, the Guzmans handed off navigation to the tower, so they weren't directly involved in orbiting the vessel either.
Even then, they knew enough to ask questions, and did.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Brugle on August 05, 2009, 08:51:29 am
But then, our pair enjoying refreshments with the planetoid's owner were also surprised by the gravity later than they should have been... so being highly automated is apparently common in this future.
They noticed weirdness in strip 198 and more in 202.  Jumping to a conclusion (that the planetoid has a higher average density than normal matter) when other explanations are possible would not be intelligent.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: jrb on August 05, 2009, 10:30:23 am
Gravity decreases with the square of the distance, regardless of source. So if this planet had 60% earth gravity at the surface, it will have 60% equivalent earth gravity at any altitude (IE, at say, 10,000ft, it will have 60% of 10,000ft gravity on earth). So in theory, the assassin should already realize how well and truly screwed he is.

Then again, this is all clearly a setup for something. Put me down for Tobi saving him.  ;)

You get it nearly correct, then contradict yourself in the second sentence.  Gravity follows an inverse-square law; if you double the distance, you decrease the gravitational force to one-quarter.  From strip 217, we know that the surface is 5km from the center of the asteroid.  Strip 202 says that the rock is out at 50km.  Ten times the distance is 1/100th the gravity, or 0.0061g.  There is no problem with the physics.  The assassin will go splat, but won't realize it until it is too late.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Rocketman on August 05, 2009, 06:33:04 pm
jrb:
    I'm going to have to disagree with you on the last point, that the assassin will go splat alright, but he won't realize it until it's too late.  Sheer instinct will tell him that he's traveling much too fast towards the ground and using his reaction gun as it shows he is he's starting to realize it.  The same way if you fall asleep at the wheel of a moving car and suddenly wake up and realize that your heading right for a tree and even hitting the breaks is not going to stop the car in time.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 06, 2009, 06:30:47 am
Gravity decreases with the square of the distance, regardless of source. So if this planet had 60% earth gravity at the surface, it will have 60% equivalent earth gravity at any altitude (IE, at say, 10,000ft, it will have 60% of 10,000ft gravity on earth). So in theory, the assassin should already realize how well and truly screwed he is.

Then again, this is all clearly a setup for something. Put me down for Tobi saving him.  ;)

You get it nearly correct, then contradict yourself in the second sentence.  Gravity follows an inverse-square law; if you double the distance, you decrease the gravitational force to one-quarter.  From strip 217, we know that the surface is 5km from the center of the asteroid.  Strip 202 says that the rock is out at 50km.  Ten times the distance is 1/100th the gravity, or 0.0061g.  There is no problem with the physics.  The assassin will go splat, but won't realize it until it is too late.

Cool, people who understand physics.  It should however be noted that his terminal velocity will be much much lower on TLP than it would be on earth.  This combined with his little adjuster gun trying to slow his decent may well make it so that he 'walks away' with only some broken legs.  Add in how advanced the medics here are, and he may well survive the ordeal.  I'd need to do a few calculations to see just what his terminal velocity would be, as I don't think it is as simple as 60% of earth's terminal velocity... Though it might be.  Anyone who has taken physics more recently than me want to verify before I break out some paper?

P.S.  Rocketman- I think by 'too late' he means after the point that he can do anything about it, which it basically was the instant he got close enough to TLP that its gravity equaled or exceeded the force that his gun thing could put out.

P.P.S.  Did the math, he should actually end up falling just a bit under 60% of earth's terminal velocity, which would put him at roughly 114 feet/s or 34.7 m/s  Still a very hard fall, and still likely deadly, but also survivable.  Any guesses on how much thrust his gun puts out?
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 06, 2009, 09:48:38 am
Cool, people who understand physics.  It should however be noted that his terminal velocity will be much much lower on TLP than it would be on earth.  This combined with his little adjuster gun trying to slow his decent may well make it so that he 'walks away' with only some broken legs.  Add in how advanced the medics here are, and he may well survive the ordeal.  I'd need to do a few calculations to see just what his terminal velocity would be, as I don't think it is as simple as 60% of earth's terminal velocity... Though it might be.  Anyone who has taken physics more recently than me want to verify before I break out some paper?

Terminal velocity has nothing to do with surface gravity. Terminal velocity is concerned with only three variables, escape velocity (a function solely of mass), distance fallen and air resistance. The velocity of objects impacting a celestial body approximate escape velocity in a vacuum. (A bit more more for objects that already had a speed exceeding escape velocity, a bit less for objects falling from less than an infinite distance.)

P.P.S.  Did the math, he should actually end up falling just a bit under 60% of earth's terminal velocity, which would put him at roughly 114 feet/s or 34.7 m/s  Still a very hard fall, and still likely deadly, but also survivable.  Any guesses on how much thrust his gun puts out?

Escape velocity for TLP is a bit under 900 kilometers per hour. If TLP had no atmosphere, our bad guy would hit at some high percentage of that speed. Because there is an atmosphere, however, he would accelerate during his fall until he reached a terminal velocity of about 200 kph. Why? Because TLP's atmospheric density is approximately that of Earth's, and about 200 kph is the fastest a person can fall through that much atmosphere, irrespective of the strength of the gravity field.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Rocketman on August 06, 2009, 10:50:27 am
Lets see 900 kph equals about 549 miles an hour minus whatever the reaction gun can slow him down and the likelyhood that he's also wearing body armor that should help keep his insides from coming outside, it's just remotely possible that he could survive this.  Many years ago I worked with a guy that messed himself up badly.  He was drunk and running his motorcycle over a hundred miles an hour when he lost control and slammed into a telephone pole.  The telephone pole was buried 6 feet into the soft sandy soil and the impact knocked it clear out of the ground but he didn't die.  One of the reasons was that he was so plastered that his body was loose.  For the next six months or so he as moving around like he was 90 years old when he was in his early 20's though.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: jrb on August 06, 2009, 11:41:51 am
jrb:
    I'm going to have to disagree with you on the last point, that the assassin will go splat alright, but he won't realize it until it's too late.  Sheer instinct will tell him that he's traveling much too fast towards the ground and using his reaction gun as it shows he is he's starting to realize it.  The same way if you fall asleep at the wheel of a moving car and suddenly wake up and realize that your heading right for a tree and even hitting the breaks is not going to stop the car in time.

That's what I meant.  He has time to realize it before he dies, but by then it is far too late to do anything about it.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Sean Roach on August 06, 2009, 01:00:45 pm
That stark terror as he can literally see death approaching at 120mph.  Couldn't happen to a more appropriate character than a cold blooded killer.  Except perhaps his paymaster.

Edit.  I don't suppose they have the technology to go through what's left of his gray matter and map out some of his memories, do they?  Perhaps not.  Hopefully they'll get his PDA mostly intact.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 06, 2009, 02:41:11 pm
Edit.  I don't suppose they have the technology to go through what's left of his gray matter and map out some of his memories, do they? 

Nope, he's brain soup.

Hopefully they'll get his PDA mostly intact.

Better than that.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: NeitherRuleNorBeRuled on August 06, 2009, 02:46:16 pm
Hopefully they'll get his PDA mostly intact.

There's almost certainly some information in his vehicle; of course it is likely set up to destruct if not accessed "properly".  Then again, Tobi probably has better tech to get at it than the pink man's organization.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Jtuxyan on August 07, 2009, 03:11:28 am
The radius of LP is stated to be ~5km, while the radius of the earth is 6,378.1km. By the inverse square law, then, for our party to be experiencing 60% of earth gravity on the surface of LP, it must have 1/976,323th the mass of earth. This tells us that the mass of LP is ~6.11E18 kg. At less than 1/50,000th the size of the smallest planet, Mercury, it is also 1/150th the size of Ceres, the largest asteroid on record. With that in mind, it could conceivably have gone undetected for a considerable time, not being that gravitationally significant -- only it's density makes it special.

I still strongly disagree with all of the politics presented in this comic -- but I am left with no choice but to give it the science stamp of approval!

SCIENCE
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 07, 2009, 10:16:03 am
Why? Because TLP's atmospheric density is approximately that of Earth's, and about 200 kph is the fastest a person can fall through that much atmosphere, irrespective of the strength of the gravity field.

Terminal velocity is the fastest an object can move through the atmosphere in free fall, and has nothing whatsoever to do with escape velocity.

Terminal velocity is affected by three things.  First, the density of the atmosphere, which in this case is presumed to be about the same as Earth's.  Second, the drag coefficent of the falling object.  Human is human, so his will be the same since he doesn't have a parachute.  And the final factor is the gravity by which the object is affected.  This is because gravity exerts a downward force on the object, while wind resistance exerts an upward force, which grows larger with velocity.  Thus if you have lower gravity and thus lower downward force, then you need a lower amount of wind resistance to equal that downward force, and thus you fall at a lower speed.

So you decrease the speed of an object in freefall by doing the following: increasing gas density, increase drag coefficient of the object, or decreasing gravity.  In this case the last one was achived, so he falls at a slower speed as I already stated.  A google search will tell you all of this in about 10 seconds.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 07, 2009, 10:27:28 am
.. I still strongly disagree with all of the politics presented in this comic -- but I am left with no choice but to give it the science stamp of approval!

SCIENCE

Well, I bet there are readers who see the science as a needless distraction from the politics. Oh well, that's why there are horse races.

Tell you what, if you are ready to reveal political flaws you believe you see, or better yet, offer some superior alternatives, I'm ready to discuss the issues. That is, until we get too far away from ELF and Scott pulls the plug on the discussion.   ;)
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 07, 2009, 10:47:41 am
You obviously don't know much about terminal velocity. 

And you obviously don't know much about tact, diplomacy or simple good manners. However, I am a tolerant man and readily abide children fools.

Terminal velocity is the fastest an object can move through the atmosphere in free fall, and has nothing whatsoever to do with escape velocity.

OF COURSE it does. As I stated, escape velocity is the highest velocity an object in free fall can reach. Assume a body with an escape velocity of 1 kph. Care to guess what terminal velocity would be for a man free falling from 1000 kilometers though an atmosphere with pressure equal to earth's? Hint: it ain't 200 kilometers per hour.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 07, 2009, 11:36:28 am
Terminal velocity is the fastest an object can move through the atmosphere in free fall, and has nothing whatsoever to do with escape velocity.

OF COURSE it does. As I stated, escape velocity is the highest velocity an object in free fall can reach. Assume a body with an escape velocity of 1 kph. Care to guess what terminal velocity would be for a man free falling from 1000 kilometers though an atmosphere with pressure equal to earth's? Hint: it ain't 200 kilometers per hour.


I do apologize.  I realized how tactless that was after I posted it and changed it.

Escape velocity is the velocity that an object would need to reach in order to break out of the gravitational pull of another object.  For instance a rocket needs to reach escape velocity to get into outer space where it is not longer affected (significantly) by earth's gravity.  Terminal velocity is the highest velocity an object in free fall can reach.

Quote from: Wikipiedia link=http://en.wikipedia.org/wiki/Escape_velocity
In physics, escape velocity is the speed where the kinetic energy of an object is equal to the magnitude of its gravitational potential energy, as calculated by the equation,

    U_g = \frac{-Gm_1m_2}{r}

It is commonly described as the speed needed to "break free" from a gravitational field

And it really doesn't matter how high an object falls from as to what its terminal velocity is except in that the atmosphere is less dense the higher you go, and thus has a higher terminal velocity.  Thus if you assume that air resistance slows the decent to terminal velocity before the fall ends, it doesn't matter if you fall from 200 feet or 200 light years, the terminal velocity will be identical.

So yeah, I don't really care how massive an object is, or how high it falls from, terminal velocity will not change at a given altitude (on earth) provided that it has the same drag coefficient.  Now, it is possible to go faster than terminal velocity, and it is possible to go slower than terminal velocity.  Starting from a higher altitude means that at that high altitude your terminal velocity will be higher, so thus when dropping to a lower altitude it is possible to temporarily fall faster than terminal velocity.  It is of course also possible to fall a short enough distance that you never reach terminal velocity.  Neither of those things however change terminal velocity.

Quote from: Wikipedia link=http://en.wikipedia.org/wiki/Terminal_velocity
A free-falling object achieves its terminal velocity when the downward force of gravity (Fg) equals the upward force of drag (Fd). This causes the net force on the object to be zero, resulting in an acceleration of zero.[1]

This also shows quite clearly shows that the gravity that is affecting an object factors into its terminal velocity.

So yeah, if he is a human, and is falling in an atmosphere that is roughly the same as Earth's, and has 60% of Earth's gravity at its surface, he should hit the ground at roughly 60% of a human's terminal velocity on Earth, which is roughly 120 Kilometers per hour, as I already stated. Edit: Though I suppose I did so in m/s as that is my preferred method of velocity when dealing with physics.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 07, 2009, 03:45:13 pm
I do apologize.  I realized how tactless that was after I posted it and changed it.

Accepted and I in turn apologize for my snotty retort. <shake>

... So yeah, if he is a human, and is falling in an atmosphere that is roughly the same as Earth's, and has 60% of Earth's gravity at its surface, he should hit the ground at roughly 60% of a human's terminal velocity on Earth,

I understand what the Wikipedia article is saying, however, the falling body is still has a mass of (for example) 75 kilos. I still think that mass will continue to accelerate until it reaches escape velocity, hits the ground or until air resistance equals the inertial mass of those 75 kilos. But I'm not a physicist, I only play one on the internet. Assuming, arguendo, that he hits the ground doing 120 kph, though, the result is pretty much the same. In mountain climbing there is a saying that goes something like this, "after the first 50 feet, it's all academic."
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Jtuxyan on August 07, 2009, 04:20:35 pm
.. I still strongly disagree with all of the politics presented in this comic -- but I am left with no choice but to give it the science stamp of approval!

SCIENCE

Well, I bet there are readers who see the science as a needless distraction from the politics. Oh well, that's why there are horse races.

Tell you what, if you are ready to reveal political flaws you believe you see, or better yet, offer some superior alternatives, I'm ready to discuss the issues. That is, until we get too far away from ELF and Scott pulls the plug on the discussion.   ;)

I fear such a discussion would not be productive. I'm a liberal who actually likes government and is pro-gun control and anti-religion. I think Escape from Terra is interesting, but it's as far from my beliefs as you can get.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 07, 2009, 05:20:29 pm
I fear such a discussion would not be productive. I'm a liberal who actually likes government and is pro-gun control and anti-religion. I think Escape from Terra is interesting, but it's as far from my beliefs as you can get.

Well see, we already have one belief in common.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Scott on August 09, 2009, 09:25:41 pm
Discuss away. If the topic drifts too far from EFT, I won't pull the plug but will move the discussion to the "Talk Amongst Yourselves" section and you can continue it there.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: KBCraig on August 10, 2009, 12:46:48 am
I've always considered "escape velocity" to be a misnomer, and not because it's actually a speed instead of a velocity.

The speed necessary to escape gravity's pull is anything >0, given sufficient time and fuel. "Escape velocity" refers only to kinetic energy, not powered flight.

Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 10, 2009, 01:22:55 pm
I've always considered "escape velocity" to be a misnomer, and not because it's actually a speed instead of a velocity.

I am sensing what we lawyers call "a distinction without a difference." So I'll bite, my dictionary defines both speed and velocity as "distance traveled per unit time." Am I missing something here?
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 10, 2009, 08:25:43 pm
I've always considered "escape velocity" to be a misnomer, and not because it's actually a speed instead of a velocity.

I am sensing what we lawyers call "a distinction without a difference." So I'll bite, my dictionary defines both speed and velocity as "distance traveled per unit time." Am I missing something here?

He is saying that he -isn't- talking about speed vs velocity (there are slight differences in physics), but by the fact that any speed moving away from an object with gravity will eventually get out of it's gravitaional field, it could just take a while.  He is saying it "should" be called "Escape Kinetic Energy".

And very true, 120 kph vs 200 kph, your still fairly screwed either way.  But you throw in body armor possibly absorbing some small part of the impact, his adjuster gun decreasing that by a few more KPH, and the fact that even a fall from a plane can occasionally be survived, and the kind of quick response and high grade medical treatment he could be receiving, and there is a very notable chance, especially if the plot line requires him to survive. :)
?
As for the max falling speed, think of it like this:  You stop accelerating when forces in opposite directions are equal right?  Like if you press your hands together, even though both have lots of force, neither are going anywhere.

So, since force is measure in newtons which is (kg * m)/s^2 or mass x acceleration, the downward force is based on mass and gravity (which is where we get weight from, and why you weigh different amounts on earth, the moon, and in space).  Now, the upward force is going to be based on air resistance.  No fancy formulas here, but I think we can agree that as speed goes up, air resistance goes up, thus a higher amount of force.

So, lower gravity = lower downward force.  Lower downward force = less upward force in order to have no net acceleration.  Less upward force = less air resistance.  Less air resistance = lower falling speed to achieve the air resistance needed.  Lower falling speed = lower falling speed = lower terminal velocity.

Hope that made sense.  We may learn rather soon if he survived or not though, as the medics will likely call the big man himself and say 'Yep, he's dead Jim' or 'Wow, he actually survived that.'
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Azure Priest on August 10, 2009, 09:00:43 pm
The technical difference between Speed and Velocity is that velocity has a directional component, speed does not. For example, the SPEED of light does not change, but the Velocity does when light's reflected, refracted, or in any other way is made to change direction.

None of that applies to the current discussion, however, except for the Kinetic energy being 1/2 m(ass)* V(elocity)^2.

If our "professional" skips the surface like a stone, he will have a much lower velocity (delta v), than if he hits head on. Considering his angle of descent, unfortunately, the latter is far more likely meaning his suit and body will take most if not all of the Kinetic energy of impact. As opposed to having the Kinetic energy "burned" away by friction. It's like the difference between sliding to home plate and running head first into a flagpole.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Bungalow_Bill on August 10, 2009, 10:43:15 pm
Speaking of physics, how about the sound propagation in that atmosphere? If it's anything like Earth normal, the boy must have one hell of a set of lungs in him. I mean, if that little dot is him, he's a good mile or more away and they can still hear him just fine from inside a sealed environment suit.  :D
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 11, 2009, 07:57:27 am
Speaking of physics, how about the sound propagation in that atmosphere? If it's anything like Earth normal, the boy must have one hell of a set of lungs in him. I mean, if that little dot is him, he's a good mile or more away and they can still hear him just fine from inside a sealed environment suit.  :D

Hmm, good point.  I kinda figured that sound was from something besides him shouting, or that it was simply showing that he was shouting, not that they could hear him.  Just because we 'hear' him from a place where the 'camera' is, doesn't mean that characters near the 'camera' can hear him as well.

My first thought was that it was the sound of his adjuster gun kicked up to max and firing strait down, mostly because you don't see people shouting represented by 'EEEE' generally, usually more of an 'AHHH'.  Or it could have been trying to represent the whistling sound that bombs and Wile E Coyote are famous for.

Edit: Actually, looking back, it certainly does seem as though they can hear him because Bert and Erny are looking around unable to find him, then suddenly can find him seemingly thanks to the sound.

Also, it seems that they do mention the escape velocity as being somehow mentioned as being related to terminal velocity, though I've never seen that before in my years of physics classes.  I'm sure there is some way to relate the two, but they don't seem directly related.  Anyway, the big man himself says 200 kph, but I believe that is a mistake on the part of the author, despite what a good job he did with gravity in general on TLP.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 11, 2009, 12:10:13 pm
Hmm, good point.  I kinda figured that sound was from something besides him shouting...

That is correct. He is aerodynamically very "dirty." He has his thruster device, his rifle, etc. So yeah, Wile E Coyote sound effects from his passage through the air. Speaking of the thruster device. It's thrust is pretty insignificant. It is like similar devices the astronauts use to move about in zero g. It is useful only in a zero or micro-gravity environment. It's useless on TLP.

I'm sure there is some way to relate the two (escape velocity and terminal velocity), but they don't seem directly related.  Anyway, the big man himself says 200 kph, but I believe that is a mistake on the part of the author, despite what a good job he did with gravity in general on TLP.

I think it is indisputable that escape velocity represents the fastest speed a freely falling object can attain before impacting a body. Thus, terminal velocity must always have escape velocity as an upper limit.

With regard to 200 kph, vs. 120 kph, Tobi... yeah Tobi, got it wrong. I will defer to your numbers. And just to get past the idea that our bad guy survived, let's just say he hit head first, against solid rock, at 120 kph. Brain soup. Okay?
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: J Thomas on August 11, 2009, 03:00:43 pm
Quote
I think it is indisputable that escape velocity represents the fastest speed a freely falling object can attain before impacting a body. Thus, terminal velocity must always have escape velocity as an upper limit.

Yes, if by freely falling you mean it starts out its fall at rest and doesn't get new velocity from anything but falling.

Since the gravitational force decreases with the square of the distance as everyone has agreed, he would fall slowly at first and gradually build up speed. And the air resistance is small while the speed is slow. Without working out the numbers I would consider the possibility that he doesn't build up to terminal velocity in the time he has to fall. He could still be going slower. That is, he could still be accelerating when he hits, never getting to the speed that air resistance cancels his acceleration. Or maybe the numbers would show that he does reach terminal velocity, I don't know.

For the plot, all that's important is that his brain is mushed, and that can sometimes happen on earth from a fall of ten feet or less. So there aren't any gotchas here, only yes-buts.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Suna Amlin on August 11, 2009, 11:36:06 pm
I was under the impression that this isn't really a planet and at the core is a teeny-tiny black hole...

The black hole draws like gravity but has limits of reach based on it's size which would reflect in a stronger pull as distance shrinks...   

*shrug*  just a thought ....
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 12, 2009, 07:41:21 am
I was under the impression that this isn't really a planet and at the core is a teeny-tiny black hole...

"Planet," as we have seen of late, is a rather arbitrary designation. TLP is small but massive, thus it is round due to gravity. I guess under the current IAU definition it would be a dwarf planet.

The black hole draws like gravity but has limits of reach based on it's size which would reflect in a stronger pull as distance shrinks... 

The mass of the black hole and the rest of TLP generate gravity just like any other body. The strength of TLP's gravitational pull, varies as to the inverse of the square of the distance. The question that may have you confused is, "distance from what?" The answer is almost always, "from the center of gravity." (I think there may be special cases for non-spherical shapes such as toruses, but for any generally round body, the center of gravity is treated as a point source.)
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: quadibloc on August 16, 2009, 09:00:05 am
I just realized, as I was looking for another item, and so looking back through earlier stips, that there was a tip-off about this. The assassin mused that it was odd that there was no gravity at all, instead of a little gravity, at his distance from Tobi's asteroid. Thus, there could have been any amount of gravity there - he failed to recognize that when in orbit, one is in free fall. So that tells us he didn't check his orbital characteristics to find out what the asteroid's mass was.

I haven't quite paid the same level of detailed attention to this webcomic as I do to Girl Genius.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Azure Priest on August 19, 2009, 11:10:48 pm
well if not "brain soup"ed, then lobster boiled. The entry angle with the most chance of impact survival ALSO generates the most heat from friction. There's also "chest tererium", "spine impalement", "boulder kiss" and all other rather ghastly forms of death from impact. Considering his last close-up, I'm going with "chest tererium" where his ribs break free of the rib cage and pierce his internal organs.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Brian on August 22, 2009, 03:39:03 am
I want to front-load my comment about the physics in the comic by stating I'm a Ph.D student studying physics and have a B.S. in physics/astro and a minor in math.

You do a damn good job on the physics.  I'm impressed.  Any occasional 'oops' is trumped by the great story and overall feeling of the comic.

Keep up the good work.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Karadan on August 24, 2009, 07:36:11 pm
TLP is small but massive

I love it when people know the definitions of words.

That would make a great shirt.  The letters TLP around the top of a picture of TLP, with the words 'small but massive' underneath.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 25, 2009, 01:37:56 pm
I want to front-load my comment about the physics in the comic by stating I'm a Ph.D student studying physics and have a B.S. in physics/astro and a minor in math.

If you don't mind, I would like to tap you for future physics issues. Please send me your e-mail in a private message.

You do a damn good job on the physics.  I'm impressed.  Any occasional 'oops' is trumped by the great story and overall feeling of the comic.

We try to get it right. Thank you for your kind words. Feel free to call oopses to attention. We need all the help we can get.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Lee A. on August 28, 2009, 04:10:33 pm
#1. It's science Fiction. In Science Fiction things can happen any way the author chooses. It doesn't have to make sense.
#2. It's a comic.  It's a funny book. nothing to get all excited about. It's not life changing you know. (If it is for you, seek help.)
#3. The writer and artists can do it any way they please. It's their work. It's their art. It's their idea.  Questions?  See #1, and #2.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Sean Roach on August 28, 2009, 11:15:32 pm
Nitpick.
#1, it's science fiction.  In fantasy the author can get away with whatever.
Fortunately, our authors are good about staying within what might be.
#2, it's political, and deliberately so.  The idea IS to change your way of thinking, which pretty much does change your life.  Still, it's a fun read, or else no one would bother.
#3, still valid.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on August 29, 2009, 11:49:24 am
#1. It's science Fiction. In Science Fiction things can happen any way the author chooses. It doesn't have to make sense.
#2. It's a comic.  It's a funny book. nothing to get all excited about. It's not life changing you know. (If it is for you, seek help.)
#3. The writer and artists can do it any way they please. It's their work. It's their art. It's their idea.  Questions?  See #1, and #2.

Yes, ultimately it is our universe, but for me, if it is science fiction, not everything can happen, otherwise it is fantasy. So that means that I do not want to deviate too far from science as it is currently understood. If I am going to speculate about something that could be true, like the nature of the surface of Ceres, that is legit, though my guess is based in some knowledge of the planetoid. When I am running in advance of current technology, with things like "meat gourd" chimeras, I try to make it a scientifically valid extension of biotech. Finally, when I go completely off the hook and speculate about quantum entanglement actually being used to communicate classical information, well, while it doesn't appear to work that way, maybe scientists will discover there is a work-around.

That's me. I appreciate corrections and critiques of any bad science that is not meant to be incorrect. Those of you who just want to go along for the roller coaster are aces with me. Those who want to question--even nitpick--are encouraged to do so, up to a point. The purpose of EFT is to entertain and if along the way it makes you think, that is gravy.
Title: Surface Area Usage
Post by: Daavik on August 31, 2009, 05:31:52 pm
So if I'm figuring this right assuming the radius of "the little prince" is 5km that means a surface area around 314 sq km.  30 (10%) for fresh water, 180 (57%) for salt water, and only ~104 km left for living on.  That's a nice size for a small population but it still seems that the salt water area is larger than really needed especially if you need room for homes, research facilities, land recreation areas, farming, etc.
Title: Re: Surface Area Usage
Post by: SandySandfort on August 31, 2009, 08:42:28 pm
So if I'm figuring this right assuming the radius of "the little prince" is 5km that means a surface area around 314 sq km.  30 (10%) for fresh water, 180 (57%) for salt water, and only ~104 km left for living on.  That's a nice size for a small population but it still seems that the salt water area is larger than really needed especially if you need room for homes, research facilities, land recreation areas, farming, etc.

TLP is more of an estate than a world. The population will never be very large. Tobi likes sailing so there is an "ocean." The islands will be seeded with wildlife (including some surprises). With some minor exceptions there will be no farming beyond hydroponics, aeroponics and personal gardens.

(BTW, just to complicate matters, the strip's TLP is different from the original short story's TLP. Short story TLP is 6.133 in diameter instead of 5.133.)   :P
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: Sean Roach on November 12, 2009, 06:45:25 am
Must be a fluke then.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: MacFall on July 16, 2010, 09:08:10 am
I was thinking of ripping off borrowing the Little Prince concept for a story I'm writing (giving credit of course), with a few modifications. I posted the idea on a forum for sci-fi fans and asked any physicists in the house to critique it (I'm no scientist myself, and I don't plan on writing strictly "hard" science fiction but I also don't want to make any really stupid mistakes).

Anyway, the physicists seem to think that even a microscopic black hole would compress a planetoid the size of the Little Prince into the size of a golf ball fairly quickly. I.e., using an historical time scale rather than an astronomic one.

I don't know how much research you've done on this - more than me, I'm sure - but there seems to be a consensus to the effect that it wouldn't work very well. Which sucks for me, because now I'm back to O'Neill Cylinders and those aren't nearly as badass as mini-planets with black holes in.
Title: Re: Surface Area Usage
Post by: J Thomas on July 16, 2010, 09:36:57 am

TLP is more of an estate than a world. The population will never be very large. Tobi likes sailing so there is an "ocean." The islands will be seeded with wildlife (including some surprises). With some minor exceptions there will be no farming beyond hydroponics, aeroponics and personal gardens.

Unless he's willing to move a lot of salt, he'll find himself with the amount that's in the rocks he uses. If they don't have much then he'll have a fresh water ocean which is not so bad. If they have excess then he'll need to get rid of some of it or else accept a dead sea with at best brine shrimp.

He could easily wind up with too much arsenic, too much of various heavy metals, too much or too little phosphate, etc etc etc. Our oceans have equilibrated through a very long process that involves water sucked deep and heated and sent back with different minerals, biological processes removing stuff, etc. It might be hard to duplicate. Something you could spend centuries tinkering with. So in the short run it might make sense to arrange to get fresh water some places, and accept that you'll have a wastewater ocean that comes out however it comes out, and you can pay somebody to spend the rest of his life figuring out how to improve it.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on July 16, 2010, 05:53:47 pm
I was thinking of ripping off borrowing the Little Prince concept for a story I'm writing... Anyway, the physicists seem to think that even a microscopic black hole would compress a planetoid the size of the Little Prince into the size of a golf ball fairly quickly. I.e., using an historical time scale rather than an astronomic one.

The Little Prince is already compressed. Did they actually read the strip or did they just the description from you? Remember on the patio when Tobi was explaining TLP? The black hole is vanishingly small. Yes, it has a lot of gravitational attraction, but if you run the numbers, you will see that at the surface it is attenuated to less than a g. So not much up there is going to be compressed. In that conversation, Tobi explained that near the black hole, the planetoid material was compressed into neutronium and that above that, it was compressed into degenerate matter, but as you climb away from the black hole, you find normal (though highly compressed) matter, until on the surface it's less compressed than on earth. Anyway, that's how I see it.
Title: Re: Surface Area Usage
Post by: SandySandfort on July 16, 2010, 06:00:01 pm
Unless [Tobi is] willing to move a lot of salt, he'll find himself with the amount that's in the rocks he uses. If they don't have much then he'll have a fresh water ocean which is not so bad. If they have excess then he'll need to get rid of some of it or else accept a dead sea with at best brine shrimp.

He could easily wind up with too much arsenic, too much of various heavy metals, too much or too little phosphate, etc etc etc. Our oceans have equilibrated through a very long process that involves water sucked deep and heated and sent back with different minerals, biological processes removing stuff, etc. It might be hard to duplicate. Something you could spend centuries tinkering with. So in the short run it might make sense to arrange to get fresh water some places, and accept that you'll have a wastewater ocean that comes out however it comes out, and you can pay somebody to spend the rest of his life figuring out how to improve it.

Possibly true, but that's the pool boy's problem. Nanites, reverse osmosis filters, biotech (arsenic sequestering algae?), etc., can condition the water. Plus with life extension a reality, Tobi can afford to be patient. (Unless they shoot him, of course.)  :-\
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: MacFall on July 16, 2010, 07:03:05 pm
I don't know if they read the comic or not. I did link to it.

Anyway, it won't work for my story because the planetoids are being built rather than found like the LP was. Making a black hole can be explained with believable sci-fi tech; just inventing enough matter to make planets with Earth-like gravity within the solar system cannot. They might as well just be building Earth-size planets out of asteroids and comets and Saturn's rings.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: wdg3rd on July 17, 2010, 01:04:18 am
I was thinking of ripping off borrowing the Little Prince concept for a story I'm writing... Anyway, the physicists seem to think that even a microscopic black hole would compress a planetoid the size of the Little Prince into the size of a golf ball fairly quickly. I.e., using an historical time scale rather than an astronomic one.

The Little Prince is already compressed. Did they actually read the strip or did they just the description from you? Remember on the patio when Tobi was explaining TLP? The black hole is vanishingly small. Yes, it has a lot of gravitational attraction, but if you run the numbers, you will see that at the surface it is attenuated to less than a g. So not much up there is going to be compressed. In that conversation, Tobi explained that near the black hole, the planetoid material was compressed into neutronium and that above that, it was compressed into degenerate matter, but as you climb away from the black hole, you find normal (though highly compressed) matter, until on the surface it's less compressed than on earth. Anyway, that's how I see it.

Most folks got no idea how the inverse-square principle applies to gravity and other stuff.  They think if you're twice as far from the radio station, just crank up the volume twice as loud.  Shocks them when they move from an area where "classic rock" has control into a region where "traditional country" (or Hip-Hop) has that frequency.  I'd blame public education, except I went through public education (but learned to read first).
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: J Thomas on July 17, 2010, 08:38:20 am
The Little Prince is alreadyThe black hole is vanishingly small. Yes, it has a lot of gravitational attraction, but if you run the numbers, you will see that at the surface it is attenuated to less than a g. So not much up there is going to be compressed. In that conversation, Tobi explained that near the black hole, the planetoid material was compressed into neutronium and that above that, it was compressed into degenerate matter, but as you climb away from the black hole, you find normal (though highly compressed) matter, until on the surface it's less compressed than on earth.

I can imagine a problem with the neutronium falling into the black hole. The faster it falls in the bigger the black hole gets and the faster more neutronium falls in, so that there could be serious problems in historical time. I haven't done the math. The math would depend on assumptions that I can't tell are true.

I don't think this is a gotcha. We currently don't know how to make or find a microscopic black hole and the last I heard nobody knew for sure whether it's possible. We don't know how to pack neutronium around a microscopic black hole in historical time. Etc. So stabilising a black hole at the center of the neutronium (perhaps in some sort of bubble that the neutronium stays out of) is just one more thing that could be discovered in coming centuries.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: SandySandfort on July 17, 2010, 10:23:37 am
I can imagine a problem with the neutronium falling into the black hole. The faster it falls in the bigger the black hole gets and the faster more neutronium falls in, so that there could be serious problems in historical time. I haven't done the math. The math would depend on assumptions that I can't tell are true.

Our hypothetical black hole is 50 nanometers in diameter. A neutron is about one femtometer in diameter or about 1/50,000,000th of the black hole. So the temptation is to believe the black hole can eat all the neutrons very quickly. However, three factors mitigate against this.

1. The number of neutrons that can fall into a 50 nanometer hole over a given time period is still exceedingly small. The percentage change in the mass of the black hole is going to increase only very slowly even if the the neutrons could just tumble straight into it, but they can't.

2. The neutrons do not fall in a straight line. They are caught up in a rapidly spinning accretion disk that resist falling into the black hole with centrifugal force. This is much as why a soap bubble takes so long to go down the whirl pool as the shower water drains.

3. Plus massive amounts of energy in the form of x-rays and other photons are blasted out of the black hole as the accretion ring spirals inward. This causes an enormous pressure outward, which retards the neutrons as they drop into the black hole.

This all goes to tell me that if a naked micro-singularity captured a planetoid, it would take a very, very long time to eat it.
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: ZeissIkon on July 17, 2010, 01:59:55 pm
Escape velocity for TLP is a bit under 900 kilometers per hour. If TLP had no atmosphere, our bad guy would hit at some high percentage of that speed. Because there is an atmosphere, however, he would accelerate during his fall until he reached a terminal velocity of about 200 kph. Why? Because TLP's atmospheric density is approximately that of Earth's, and about 200 kph is the fastest a person can fall through that much atmosphere, irrespective of the strength of the gravity field.

Terminal velocity is a (fairly) simple relationship between air density, aerodynamic drag coefficient of the falling body, and gravity (local to the current altitude); it defines the falling rate at which aerodynamic drag equals the force of gravity.  On Earth, where gravity is effectively the same value from surface to the upper edge of the sensible atmosphere (close to the 100 km international boundary of "space"), this figure varies from over 1000 km/hr at the edge of space (where "sensible" atmosphere means you can get usable reaction against a body moving at near orbital speed) to under 200 km/hr just above the surface.  On another body with the same surface atmospheric density as Earth, terminal velocity would scale with roughly the square root of gravity (because drag scales with the square of velocity); if you have 60% gravity, your terminal velocity would be roughly 85% of the Earth surface figure -- call it 170 km/hr, or not quite twice the "double nickel" speed limit I grew up with.  Not survivable unless you land in something that slows your fall gradually.

There are recorded cases people who have survived terminal velocity falls due to falling on something that slows them gradually, rather than almost instantly like the ground or the surface of water (at 100+ km/hr vertical fall, you may as well hit concrete).  One of the best documented was a WWII gunner from a B17 who fell 20,000 feet (around 6 km) without even a streaming parachute (he couldn't wear the 'chute in the belly turret, so didn't have it with him when the turret was blow out of the aircraft), but landed on top of a tall spruce, stripping branches down one side of the trunk to the ground (and thus stopping in twenty meters or so instead of a few tens of centimeters).  On the other hand, the number of cases of this kind of survival run to around a dozen in the century or so since humans have had the ability to fly high enough to hit terminal velocity in a fall (I don't count skydivers who land with a collapsed parachute, since the streamer still significantly reduces their falling rate).
Title: Re: Physics Does Not Work that Way [Falling Assasin]
Post by: J Thomas on July 19, 2010, 02:16:40 am
I haven't done the math. The math would depend on assumptions that I can't tell are true.

Our hypothetical black hole is 50 nanometers in diameter. A neutron is about one femtometer in diameter or about 1/50,000,000th of the black hole. So the temptation is to believe the black hole can eat all the neutrons very quickly. However, three factors mitigate against this.

I find your reasoning somewhat plausible but not convincing. The pressure at the center of a big glob of neutronium....

But it isn't  important enough to me to do the math. And I'd be disappointed if you did the math when you could be telling a great story instead. I think my handwaving is adequate -- in the time between now and then there could be advances in physics that would show people how to get the effect you want.

I like it that you've thought out a plausible background that might allow the result you want. I'm sure it was fun and it adds depth to the story. Please don't let us science trolls get you arguing beyond the point it stays fun.