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Science and Astronomy Questions
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| Watsisname | Date: Tuesday, 01.11.2016, 06:51 | Message # 901 |
 Galaxy Architect
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| Quote spacer (  ) can you explain to me how to know in which diraction the Net force is?
like in the second law questions
when i draw it like in what you did i have hard time to find the net force. the mg and normal force are ok but the net force i always stop there.
Ah, well there's a few things to say about that. First, have you been introduced to vectors and how to add them? If not, then you don't need to worry about the drawing. 
How to know the direction of the net force.
In this case, we know the direction that you are accelerating. It must be upward, same as the elevator. Then we know the direction of the net force (the combination of all the forces acting together) on you as well. Newton's Second Law says the direction of the net force on an object is the same direction as its acceleration.
Now what if we are trying to find the net force, but don't know the acceleration? What if all we know are the directions and magnitudes of each of (possibly several) forces acting on it? In that case, we can use vector addition. The idea is to represent each force with an arrow, whose direction corresponds to the direction of the force, and its length corresponds to the magnitude of the force. Then the net force is found by drawing all the vectors together, tip to tail. A youtube video explaining this can be found here (particularly from 3:35 to 7:55).
Also, I forgot you asked for further examples to practice on with density. So I'll give you one. Hopefully not too challenging, but I also don't want to make it trivially easy.
Consider the Earth. Our beautiful blue planet. 
Let's crush it until it becomes a black hole.
My question for you is:
How dense would the Earth be, right at the moment we crushed it enough to form a black hole?
Got it? Okay, here is some helpful info:
Einstein's theory of general relativity tells us that any object will become a black hole, if it is compressed within a sphere of a certain critical size. The radius of that sphere (which we call the "Schwarzschild radius") depends only on the mass of the object itself, and a few constants of nature. The formula is:
where:
G is the gravitational constant: 6.67x10-11 m^3/kg/s^2 (meters-cubed per kilogram per second-squared),
M is the mass of the object (Earth = 5.97x1024 kg)
c is the speed of light (3.00x108 m/s)
Good luck!
Added: Oh, and let's say you have until November 13 and I'll post the solution then. I don't want you to feel pressured to work on it too quickly.
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| spacer | Date: Tuesday, 01.11.2016, 15:41 | Message # 902 |
 Star Engineer
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Israel
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| Watsisname, mmm didnt understand much how to do the massxgravitational constant.
6.67x10-11 m^3/kg/s^2x5.97x10^24 kg?
"we began as wanderers, and we are wanderers still"
-carl sagan
-space engine photographer
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| Watsisname | Date: Tuesday, 01.11.2016, 17:03 | Message # 903 |
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Galaxy Architect
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| Yes, the way you wrote it is exactly right.
The mass and the gravitational constant are numbers, but both numbers have units associated with them. In the MKS ("meters-kilograms-seconds") metric system, mass is measured in kilograms, and the gravitational constant is measured in cubic meters per kilogram per second-squared.
If we multiply G by M, then the units will be (m^3)/(kg*s^2) multiplied by (kg). The kilograms will cancel, leaving (m^3)/(s^2). Then you'll get new units again after you divide by c^2. Indeed, it should simplify to just meters, since the units on the right hand side of the formula must be the same as the units on the left hand side. The left hand side is R (radius), which is in meters.
This technique of working with the units, or "dimensions" of the quantities in a calculation is known as "dimensional analysis", and is a very useful tool.
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| steeljaw354 | Date: Tuesday, 01.11.2016, 21:37 | Message # 904 |
 World Builder
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Pirate
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| What if Jupiter was a brown dwarf?
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| Alek | Date: Wednesday, 02.11.2016, 04:32 | Message # 905 |
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| Quote steeljaw354 ( ) What if Jupiter was a brown dwarf?
I'll run a Universe Sandbox simulation overnight and inform you of the answer tomorrow.
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
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| Alek | Date: Wednesday, 02.11.2016, 17:33 | Message # 906 |
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| So, if Jupiter was 30 times its current mass, but had about the same orbit, then within just a few thousand years it would make all the planets beyond its orbit be pulled inward in such a way that the orbits would be very eccentric and Saturn would be in danger of being slingshotted out of the solar system completely. As for the inner solar system, the orbits would stay stable but Earth might get hit with a few asteroids because eventually Jupiter's gravity would slow down most of the asteroids in the asteroid belt, especially the smaller ones, and they would fall into the inner solar system.
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
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| steeljaw354 | Date: Wednesday, 02.11.2016, 19:02 | Message # 907 |
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World Builder
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| I mean if it was like that from the start if it formed that way.
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| Alek | Date: Wednesday, 02.11.2016, 19:21 | Message # 908 |
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| Quote steeljaw354 ( ) I mean if it was like that from the start if it formed that way.
Oh
Well in that case, the planets that are now beyond Jupiter would probably have to be farther away from the sun then they are now, and Saturn would probably be either smaller or nonexistent, there would be no asteroid belt and most of that debris would probably be moons of Jupiter or would be Earth-orbit-crossing asteroids, and Mars might either be smaller or more likely nonexistent, and due to the higher number of impacts here on Earth, life would either not exist or be very different.
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
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| Alek | Date: Wednesday, 02.11.2016, 19:23 | Message # 909 |
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| Also,
Quote Alek ( ) I don't remember where, but I read an article that states how this "uncertainty" came about and did so in a non misleading way (aka not leading you to believe scientists have thrown out the accelerating universe model, since they explained that the observational data is technically within the margin of error but the measurements agree enough that the theory can't simply be considered rubbish and random chance/noise)
Here's the article I was talking about.
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
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| PlutonianEmpire | Date: Thursday, 03.11.2016, 04:15 | Message # 910 |
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| Here's something more in the realm of psychology: Why do most people find extremely high fields of view attractive, in terms of pictures and video game screenshots? Or why are wide fields of view considered pretty and low fields of view considered ugly?
Specs: Dell Inspiron 5547 (Laptop); 8 gigabytes of RAM; Processor: Intel® Core™ i5-4210U CPU @ 1.70GHz (4 CPUs), ~2.4GHz; Operating System: Windows 7 Home Premium 64-bit; Graphics: Intel® HD Graphics 4400 (That's all there is :( )
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| Watsisname | Date: Thursday, 03.11.2016, 05:48 | Message # 911 |
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Galaxy Architect
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| Interesting question! My guess (and it totally is just wild speculation) would be that it derives from our hunter-gatherer days. Being able to see a wider view of your surroundings is beneficial to gather information about food, resources, predators or rivals and approaching weather. It could be related to why we associate views from high places and mountain tops as being aesthetic.
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| Alek | Date: Thursday, 03.11.2016, 14:29 | Message # 912 |
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| Quote Watsisname ( ) It could be related to why we associate views from high places and mountain tops as being aesthetic.
Which just so happens to be where I take 95% of my SE screenshots 
EDIT: Okay, so, not sure where else to post this, so I will here. Is there currently any software out there right now that can test the stability of orbits over millions or billions of years in a reasonable amount of time (aka not having to dedicate 5 years of my life to wait for a simulation to run a few million years accurately)?
EDIT 2: Also, I've looked everywhere, but is there some sort of substance that could be a liquid with a lower viscosity than glass in a -19.84°F, 0.0247 Atm pressure environment? (It wouldn't have to have water-like viscosity, maybe more like lava? Just something that could move in a reasonable amount of time. Even if it evaporates after a few hundreds or thousands of years, if I can find a way to renew the supply, having it evaporate after awhile would be okay.)
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
Edited by Alek - Thursday, 03.11.2016, 18:19 |
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| Watsisname | Date: Friday, 04.11.2016, 03:10 | Message # 913 |
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Galaxy Architect
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| Quote Alek ( ) Is there currently any software out there right now that can test the stability of orbits over millions or billions of years in a reasonable amount of time (aka not having to dedicate 5 years of my life to wait for a simulation to run a few million years accurately)?
Indeed! There are packaged codes for n-body integrators using a variety of methods, and professional astronomers often use these to study the dynamics and stability of planetary systems. I don't have any experience in this area though, so I'm not sure how difficult it will be to learn how to use them.
https://www.boulder.swri.edu/~hal/swift.html
As for your second question... are we talking of substances which are common in nature, or can it be anything? I'm having a real hard time thinking of anything for this, but maybe Mercury works? This is the only reliable phase diagram I can find though, and it's definitely not clear as to what happens in the low-pressure regime. In these units you're looking at 0.000025 kbar and 244.4 K.
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| Hornblower | Date: Friday, 04.11.2016, 14:46 | Message # 914 |
 World Builder
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| Ok, here's a tough one that I'm dying to know the answer to; What would it be like to have causation without correlation. At first glance it seems impossible, but there could be something.
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| Alek | Date: Friday, 04.11.2016, 15:49 | Message # 915 |
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Pioneer
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| Quote Watsisname ( ) Indeed! There are packaged codes for n-body integrators using a variety of methods, and professional astronomers often use these to study the dynamics and stability of planetary systems. I don't have any experience in this area though, so I'm not sure how difficult it will be to learn how to use them. https://www.boulder.swri.edu/~hal/swift.html
Considering that I have practically no knowledge of programs like that (ones where "parameters" are entered into some type of text file and then the whole thing still needs to be complied) that would be quite difficult, but I guess thats to be expected, since basically everyone using that niche of a program is probably a researcher, which of course would know these things.
Quote Watsisname ( ) As for your second question... are we talking of substances which are common in nature, or can it be anything? I'm having a real hard time thinking of anything for this, but maybe Mercury works? This is the only reliable phase diagram I can find though, and it's definitely not clear as to what happens in the low-pressure regime. In these units you're looking at 0.000025 kbar and 244.4 K.
In this case, as long as it's not too complex of a substance (i.e. the only way it could possibly be made would be through mankind) pretty much anything would work, though the more common the material the better. Mercury seems to work according to that, but I agree, it is sort of unclear, and only barely works..
Too bad Thermo-calc is a hassle to get and seems to be more for metallurgy researchers and the academic version is limited as such that I probably wouldn't be able to find what I'm looking for...
Living among the stars, I find my way. I grow in strength through knowledge of the space I occupy, until I become the ruler of my own interstellar empire of sorts. Though The world was made for the day, I was made for the night, and thus, the universe itself is within my destiny.
Edited by Alek - Friday, 04.11.2016, 15:53 |
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