Joined: May 2005 Gender: Male Posts: 3,144 Location: Hamilton, Ontario
Re: Can't register? « Result #2 on Mar 22, 2013, 3:18am »
Hi George,
Sorry about that. The forum is currently down due to some unexpected server issues. But once it is back (hopefully soon!) please go ahead and register again. I'll make sure you are approved this time.
I was able to create a new account without any error messages.
I can ask Proboards Tech Support about the problem, but I'll need more information. What browser are you using? Are you accessing the forum through a proxy server?
Hi LunarOrbit, I have tried unsuccessfully to register a couple of times now... perhaps its my ISP address being on your 'suspect list' as I have read on here that you have spamming from lots of ISP address!
I live in the Czech republic and my ISP is 194.228.20.164...hope I can join soon, great forum with some obviously talented people.
Joined: May 2005 Gender: Male Posts: 3,144 Location: Hamilton, Ontario
Technical difficulties « Result #4 on Mar 2, 2012, 1:04am »
Looks like my web host is experiencing some kind of technical difficulties because not only is ApolloHoax.net down, but so is their website. Hopefully everything will be back soon.
It's midnight here and I'm going to bed. If it's not back by the time I wake up I'll try to get some answers.
Joined: May 2005 Gender: Male Posts: 4,620 Location: Lost Deimos Moonbase
Re: The "DPS should have dug a blast crater" Meme « Result #6 on Feb 22, 2012, 10:21pm »
Quote:
But when cooking from the hip I can guess better in Fahrenheit, but only because I've been using those units all along. I would expect my counterpart in Italy to be more familiar with Celsius oven settings and what you cook at what temperature.
Depends on what you are cooking, but in general for something you want to slow cook probably 180, for a cooking but not making crunchy go for 200, and to get that crunchy crispy outer, 230.
« Last Edit: Feb 22, 2012, 10:22pm by PhantomWolf »
It must be fun to lead a life completely unburdened by reality. -- JayUtah
"On two occasions, I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question." -- Charles Babbage (1791-1871)
Please feel free to register. In order to weed out spammers I have it set to require my approval for new accounts. Registering with the same name that you use here will make it easier for me and will speed up the process. I'll try to approve accounts as quickly as possible.
I will be locking this forum probably over the weekend, so I highly recommend that you don't start any new threads here. For existing threads I suggest starting a thread on the new forum and continuing the discussion there. You can quote the last post of the old thread and link to it if you'd like.
Also, if anyone would like to copy the first post of a thread that they started here then by all means, I think that would be a good idea. I can copy individual posts myself, but they will have my name assigned to them so it's better if the original author copies them.
I hate that I have to say this, but please do not register using the name of anyone else here.
Jay, I am not going back to the site. But I was interested as this guy seemed to have actually put some effort into the drawings and calulations unless he got them from someone else. I had never seen this kind of effort outside of YouTube.
Ranb
It was frenat. Same as I use everywhere. I only used the account to track the nonsense posts there anyway.
Update: I was contacted (by PM) by Rerevisionist, the moderator of that forum, and he said he reactivated my account. They periodically make accounts inactive if they haven't posted. I mentioned that I may not post, that I mainly used the account to track new posts. His next PM revealed he didn't even know what that meant and that even unregistered users could read all posts. I explained that only if you were registered with an active account could you get emails informing you of new posts. His response? A Pm that I can't read as my account is now inactive again. How open-minded!
I've heard from other people ka9q's complaint about the relative obscurity of the slug unit, but to me, who cares?
Indeed, how many non-scientist Europeans know what a newton is or how to use it?
Quote:
When dealing with Apollo related stuff I'm often back to using EES because that's what we see in the NASA documents.
...who were technically required to use SI but habitually received a waiver on the grounds that the contractors' knowledge base and designs were in EES. Clavius uses both: EES in main text, SI in parentheses. But this is sporadic because I grow bored doing comprehensive checks of the site for such consistencies.
Quote:
For instance, I can't visualize the stature of a man 180 cm tall and 85 kg, but I can someone 5'-11" and 187 lbs.
Indeed, the larger question for non-scientist users is familiarity in the face of arbitrary definitions. At a certain point a temperature is just an arbitrary setting on the oven knob, and it largely doesn't matter to me what the actual number is as long as the recipe and the knob agree. But when cooking from the hip I can guess better in Fahrenheit, but only because I've been using those units all along. I would expect my counterpart in Italy to be more familiar with Celsius oven settings and what you cook at what temperature.
I had a nice long post explaining all about why to and not to include gravity, but Explorer crashed
I hate it when that happens.
Let me also add to your explanation that when a body moves horizontally, there is no change in its potential energy. When energy is added to the body it's all kinetic.
As a body moves upward, its potential energy increases as altitude is gained. The gain in potential energy comes at the sacrifice of kinetic energy. As kinetic energy decreases, so does velocity.
Someone who weighs himself in the bathroom at 51 kg that morning and goes to work as an engineer dealing with forces in newtons is going to have just as much mental anguish as the person who weighs himself at 112 lbs and then has to go to his own engineering office and reckon the mass of a beam in slugs.
I agree. Both systems are valid and I don't think it makes a bit of difference which system is used. I've heard from other people ka9q's complaint about the relative obscurity of the slug unit, but to me, who cares? It doesn't matter to me whether or not my barber knows what it is, all that matters is that my engineer and scientist colleagues know what it is.
Putting aside the fact I made a stupid mistake earlier today, I'm generally comfortable with either system of units. In my job (US construction industry) I work almost exclusively in EES. For my web page I prefer SI because I have international readers. When dealing with Apollo related stuff I'm often back to using EES because that's what we see in the NASA documents. I definitely prefer SI for anything having to do with thermodynamics.
When solving problems related to my rocketry or aerodynamics studies, I prefer working with SI units; however, I have trouble getting a feel for measurements in SI. For instance, I can't visualize the stature of a man 180 cm tall and 85 kg, but I can someone 5'-11" and 187 lbs.
Joined: May 2005 Gender: Male Posts: 4,620 Location: Lost Deimos Moonbase
Re: The "DPS should have dug a blast crater" Meme « Result #13 on Feb 22, 2012, 5:27pm »
I had a nice long post explaining all about why to and not to include gravity, but Explorer crashed, and since Prof is likely to ignore it anyway......
So the abridged version...
F = mat
where at = a + gp
and gp is the acceleration vector component of gravity in the plane of the Force vector we're looking at
Now we have two basic situations, one is where our plane is vertical to the local gravity field and so gp = our local g and where the other is when the plane is horizontal to the local gravity field and so our gp = 0m/s2 regardless of where it is in the universe because gravity is a vector that has no horizontal component to it. (Note that a combination of these two planes can be used to represent any force vector possible which is why they are the simplest planes to work with to demonstrate the point.)
So given that...
F = m (a + gp)
First let's take a hovering spacecraft of mass 2,500kg. Since it is hovering, a = 0m/s2
Since we are dealing with the Vertical Plane we know that;
On Earth gpv = 9.81m/s2 On Moon gpv = 1.63m/s2
so on Earth...
F = m (a + gpv)
F = 2500kg (0ms2 + 9.81m/s2) F = 2500kg x 9.81m/s2 F = 24,525N
On the Moon
F = m (a + gpv)
F = 2500kg (0ms2 + 1.63m/s2) F = 2500kg x 1.63m/s2 F = 4,075N
Hopefully this expains why you need less thrust on the moon, it's not the mass that has changed, but the acceleration you need to overcome.
Now let's look at a ball moving horizontally in both places. Remember that in the horizontal plane, gph = 0m/s2 because gravity has no horizontal component.
Our ball will have a mass of 0.5kg and we'll throw it with an acceleration of 48m/s2 taking 1s to do it.
so on Earth...
F = m (a + gph)
F = 0.5kg (48ms2 + 0m/s2) F = 0.5kg x 48m/s2 F = 24N
On the Moon
F = m (a + gph)
F = 0.5kg (48ms2 + 0m/s2) F = 0.5kg x 48m/s2 F = 24N
Note that the answer is identical in both equations. Force that is horizontal to the local gravity vector doesn't change regardless of where it is in the universe.
So how does that effect the energy?
Well Ek = ˝F.a.t2
so regardless of where the horizontal force occurs, the Ek it transmits will be the same.
In the case of the balls in the above example, 576J
This should also explain why your don't change the density (which is mass/volume) as mass doesn't change, and why you don't consider gravity when dealing with horizontal motion, such as dust being blown across a surface.
ETA: Something I should have noted, and did in the longer version (yes it was longer ) is that while the ball leaves our hand with the same velocity in both examples (since v = at and a and t are the same in both examples) it will go futher on the Moon because after leaving our hand the lower gravity means it will take longer to reach the ground allowing it to travel a much greater distance.)
« Last Edit: Feb 22, 2012, 5:42pm by PhantomWolf »
It must be fun to lead a life completely unburdened by reality. -- JayUtah
"On two occasions, I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able to rightly apprehend the kind of confusion of ideas that could provoke such a question." -- Charles Babbage (1791-1871)
Re: The "DPS should have dug a blast crater" Meme « Result #14 on Feb 22, 2012, 4:42pm »
A lot of engineering still occurs on Earth rather than in space or on other planets, and so a lot of practical engineering still involves dealing with the force of Earth gravity on some sort of mass. This is what continues to motivate a "simple" system of units that requires few arbitrary conversions.
The metric-speaking world still weighs things in kilograms. The imperial-speaking world still weighs things in pounds. This is because our knee-jerk reaction is always still to determine mass by measuring the force of Earth gravity on it. The casual users of both systems just happened to have fallen on different sides of the fence about which unit to use as the practical measure for non-engineering purposes.
But each tradition has created a consistent subset of units that serves formal engineering. One engineers in SI, not metric. One also engineers in EES, not imperial. The flaw in both approaches comes from reusing familiar quantities and concepts from the looser parent systems. Someone who weighs himself in the bathroom at 51 kg that morning and goes to work as an engineer dealing with forces in newtons is going to have just as much mental anguish as the person who weighs himself at 112 lbs and then has to go to his own engineering office and reckon the mass of a beam in slugs.
Once you realize that all the units involved are arbitrary, regardless of the system, and that the problems we face come not from the beauty or clunkiness of the system but from the inherent inconsistency in the problems we want to solve, the advocacy of one system over another becomes distractive. Yes, standardization is a good goal. But as long as our intuitive notion of mass is so inexorably connected to our planet's gravity, we'll have this problem.
Joined: Aug 2005 Gender: Male Posts: 86 Location: Washington
Re: New version of painted backdrop claim? « Result #15 on Feb 22, 2012, 3:57pm »
frenat, what name did you use on that site?
Jay, I am not going back to the site. But I was interested as this guy seemed to have actually put some effort into the drawings and calulations unless he got them from someone else. I had never seen this kind of effort outside of YouTube.
To be of any practical relevance in demonstrating the lack of a crater it must be demonstrated how 2,644 pounds of thrust will have a negligible effect on an area with lunar regolith that has the effective weight of powdered milk. Someone blowing 5 times into powdered milk will create a deeper crater then is being predicted with a lunar lander.
When you blow into a substance it's not flying away at 1000+ m/s.
You're making the same mistake that a lot of other people make. You seem to believe that adding a large amount of energy to the soil must mean that a large volume of soil is transported away. That is not the necessary requirement. Adding a large amount of energy to the soil can also mean that a small volume of soil is transported away at a very high velocity. Kinetic energy is mv2/2, so a small mass of material at high velocity can have the same kinetic energy as a large mass at low velocity. We know from observation that the soil flew away at very high velocity, so we should expect the volume of material to be small rather than large.
We know the kinetic energy in the exhaust with good confidence. We also know the amount of energy transferred to the soil can be no greater than the amount of energy that's in the exhaust. We also know the estimated velocity of the soil. Given these known values, it is straight forward math to estimate the mass of soil blown away by the exhaust. This has already been done and the answer tells us that a large crater will not form.
A 179 pound ball on earth takes 6 times more energy to move then a 179 pound (29.8 adjusted for gravity) ball on the moon.
As Jay pointed out, it only takes more energy if you are lifting the ball. Let's say we lift the ball 5 feet. At the higher elevation the ball possesses greater potential energy; we therefore have to add energy to the ball to lift it. The amount of energy added to the same ball is 6 times greater at the surface of Earth than at the surface of the moon.
However, the problem we've been dealing with involves kinetic energy, i.e. the energy of motion. A 179 pound-mass ball moving at, say 10 ft/s, has the same kinetic energy on Earth as it does on the moon.
Re: The "DPS should have dug a blast crater" Meme « Result #18 on Feb 22, 2012, 3:07pm »
I understand what you are saying concerning energy transfer. These equations predict 100% transfer of energy at maximum velocity, which does not seem realistic or possible, there would be a variation in acceleration of particles < 1,000 m & >1,000 m / sec.
To be of any practical relevance in demonstrating the lack of a crater it must be demonstrated how 2,644 pounds of thrust will have a negligible effect on an area with lunar regolith that has the effective weight of powdered milk. Someone blowing 5 times into powdered milk will create a deeper crater then is being predicted with a lunar lander.
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) is that while the ball leaves our hand with the same velocity in both examples (since v = at and a and t are the same in both examples) it will go futher on the Moon because after leaving our hand the lower gravity means it will take longer to reach the ground allowing it to travel a much greater distance.)
