-Velocity-

Apathy, ignorance, and human stupidity are what killed space exploration. If the public had more of a hunger for it, the politicians would follow.

Here's some plots demonstrating the paradoxical link between increased dust in the air and decreased dust on the MER solar panels. Both of the plots are from the same source. Spirit- Opportunity- Both images- P. M. Stella and J. A. Herman, “The Mars surface environment and solar array performance,†in Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE, 2010, pp. 002631–002635. The "dust factor" is a measure of the amount of sunlight that makes it through the dust layer on the solar cells, so the higher the dust factor, the less dust (the maximum value is 1.0, of course, where 0% of sunlight is blocked by dust accumulation on the solar cells). Tau is an expotential term that's related to the amount of direct sunlight that makes it to the surface. Basically, the rovers would take a picture of the Sun, and its brightness would be used to compute the atmospheric extinction tau value according to the formula I = Io*exp(-tau) where I = observed intensity of sun Io = known actual intensity, no extinction ANYWAY, observe the cyclical pattern of tau values. At a periodic interval, tau tends increase, typically with three spikes. This increase corresponds to the powerful summer hemisphere summer, where the high eccentricity of Mars' orbit brings it closest to the Sun simultaneously to the southern hemisphere experiencing its summer season. This leads to a lot of dust storms. Notice that the dust factor (inversely proportional to the amount of dust covering the arrays) tends to be the highest during this stormy, dusty season on Mars. This is especially true for Spirit. This is because, like I said, the winds that bring dust into the air also clean the dust off the panels. The amount of dust cleaning by these winds was unexpected, and this is really what allowed the rovers to last so long. - - - Updated - - - Finally, notice the huge jumps in dust factor- sometimes it will increase all of sudden. These are known as "cleaning events". We believe that the MERs get struck by large, random gusts of wind- perhaps even dust devils, and these gusts remove a huge amount of the dust accumulation all at once. These also tend to happen during the stormy, dusty season on Mars, but are a bit more random. Here's a before and after image of a rover's sundial. I believe this is from the big the cleaning event Spirit experienced during its first Martian year (see the plot for MER-A above).

Incorrect, here is a quote from a paper on the subject- P. M. Stella and J. A. Herman, “The Mars surface environment and solar array performance,†in Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE, 2010, pp. 002631–002635. The main reason the rovers have lasted so long on PV power is the unexpected cleaning events. In a nutshell, the same forces that lift dust into the air (wind) also cleans the rover's panels. When it gets really dusty, it also tends to clean the dust away too, and it ends up being a sort of self-limiting process, though things can still get bad, so both rovers also had a bit of luck. I have a power point presentation on it, but I don't know how I could share it with you guys.

Since we're already ignoring the laws of physics, I'd say create an anti-gravity field, and use the anti-gravity field to create a perpetual motion machine. Have the perpetual motion machine drive a generator that charges up some capacitors. Once the capacitors are at full charge, you discharge them as the power source for a particle accelerator that creates antimatter. Cool the antimatter and store it in a magnetic trap. Keep doing this for a while, then hold the alien planet for ransom with your giant antimatter ball.

They will probably just get hot, as they're dropping all their voltage across their internal resistances, but some battery types can certainly catch fire or explode, as already mentioned by others. Several years back, I made the mistake of putting a mostly discharged 9 V battery in my pocket. There was some loose change in there too, and one of the coins shorted the two terminals together. Next thing I knew, something in my pocket was most uncomfortably warm (and getting warmer), and I had to empty my pocket pronto!

Exactly, but it would be a fairly small resistance, so it might be possible to damage your good battery from having too high of a current.

Newtons are used by engineers and scientists constantly, for any unit that involves force. I look at it differently. When your friend says, "I weigh 70 kilograms", what he is really meaning is "I mass 70 kilograms", because we know he lives on Earth. If he were to say "I weigh 70 kilograms", and he lived on Mars, then you'd have to ask him what he meant. But it is true that scales that give weights in kilograms are actually measuring kilograms force, unless it's a balance scale.

Not quite a short circuit, but you're right that it's generally a bad idea to connect a fully charged battery to a fully discharged battery. However, there's nothing necessarily wrong with putting batteries of the same type and same charge level in parallel.

Not quite, the internal resistance only dissipates power if there is current flowing. The battery with less charge would stop charging when the open-circuit voltage of the two batteries is equal. In other words- equal voltage when disconnected (no current flowing) = no current flowing when the two batteries are connected together, because you need a voltage difference for there to be a current flow.

I know, but it's not going to be used in physics or in a physics book. Let's not confuse the guy, please. At least he doesn't have to do some problems in U.S. customary units, like physics books here in the U.S. will do. They'll throw in a problem where everything is in feet, inches, gallons (or, God forbid, tablespoons), pounds force, pounds mass, PSI, horsepower, etc. Those problems are most easily solved by just converting the initial problem statement into SI, solve the problem, then convert the answer back to U.S. customary to make the book/teacher happy.

I didn't say brighter, I said they remain in sunlight when the rest of the crater is in shadow. Have you not seen this picture yet? See how the spots remain illuminated by the Sun when the rest of the crater is mostly in shadow? That is an obvious indication that the spots can't be in a deep depression, and they really are probably on the top of a hill or mountain. The brightest spot is even right where you'd expect the central peak of a crater to be.

The unit of force is Newtons. Weight is force generated by the product of mass (kg) and gravitational acceleration (m/s^2), and is given in Newtons as well. People sometimes (incorrectly) give weight in kilograms, because we all feel about the same gravitational acceleration.

No, it actually looks like these features are at high altitudes, as they are in light when most of rest of the crater floor is in shadow.

Is styrolit the name of the material the floor was made out of? I didn't really understand the questions if not. I think the OP needs a basic physics book, like a high school textbook. If he/she going to hopefully go to college, then the college can take it the rest of the way. Also, one is going to need high school algebra skills to get started in calculus.

Don't forget you have to multiply by 9.81 m/s^2 to get the force in Newtons... kg is a unit of mass. 75 kN/m^2 is a unit of force per surface area- of pressure. So you multiply that by your surface area (12 m^2) to get the maximum force. Divide the previous answer you got (in Newtons) by 9.81 m/s^2 to convert from Newtons to kilograms. You should ignore atmospheric force, you don't build floors over a vacuum. There is going to be a roughly equal atmospheric pressure on the other side too. Unless you're supposed to factor in the buoyancy force... which would be ridiculous because it would fairly negligible. I may not be interpreting your problem right though, because they give you the thickness of the floor, I think, and you don't use it. But they often give you things you don't need in physics problems to try to trick you into using them.

Viewing light as a solely particle phenomenon, you're going to run into things that don’t make sense. Like everything else, electromagnetic radiation is a wave phenomenon, and you can’t understand how it works without acknowledging this. Let’s look at a partial example of how light reflects off of a perfect electric conductor (PEC). The electric field must go to zero in a perfect electric conductor. Metals are very close to being PECs, which is why they are “shiny†when polished smooth as compared to the wavelength of light. A PEC can support a surface charge, so they can have electric fields that are normal to their surface, but any tangential electric fields are neutralized by the flow of charge. Furthermore, the accumulation of surface charges screens any normal electric fields and prevents them from penetrating into the PEC. For simplicity, I’ll only show you half of a solution- I’ll only look at electric fields and one polarization case, but it will hopefully get the point across. Imagine an incident electromagnetic wave coming in from a random angle. In this example, the polarization is such that the electric field is tangential to the surface of the PEC. When that electromagnetic wave reaches the surface of the PEC, the boundary condition of the PEC- that tangential electric fields go to zero- forces the surface to "launch" a reflected wave that exactly cancels out the electric field right at the surface boundary. There are boundary conditions that apply for magnetic fields too, and that relate them to surface currents, and these are equally important, but I’m trying to keep things simple here, so I’m only presenting half of the solution. Suffice it to say, the boundary conditions set that the direction of the reflected wave follows the law of reflection (the angle is the same but opposite). But hopefully, this example should get the point across that you really can’t ignore the wave nature of light. - - - Updated - - - But it's not true that the same photons were absorbed and re-emitted in route. The photons are absorbed and their identities- as much as they can be said to have identities- is gone. The photons that are re-emitted are of a different wavelength, and contain different quantum information. They are entirely different particles. Imagine that you shine an invisible ultraviolet laser beam (just as an example, but any light source of any wavelength would do for this example) on a piece of metal and heat that metal until it's glowing red-hot, then turn the laser off and record the photons emitted by the heated metal. The metal continues to glow even though the laser is off, because energy is stored in vibrations of the particles that make the metal up. The photons emitted by the red hot metal are NOT coherent ultraviolet laser light. They are entirely different photons, and emitted at a spread of wavelengths determined by the temperature of the metal and Planck's law for thermal blackbody radiation. THAT is what is going on inside the Sun. It is entirely false to claim that photons in the center of the Sun can ever make it to the surface. It is only the energy produced in the center of the Sun makes it the surface.

This is a ridiculous discussion. Things with an albedo of 0.2 are not white on any reasonable scale where white-gray-black are defined by their albedos. All you have to do is put something next to it that has an albedo of 0.9 and you will see that they do no longer appear white. Your point is non-existant because you're comparing apples and oranges. In our normal everyday experience, white-vs.-gray-vs.-black is comparative to a well illuminated background. You cannot apply your normal everyday experience to astronomy. In astronomy, the background- space- is extremely dark. So even something with an albedo of 0.001 could appear white (if it was color neutral), while on Earth, it would appear jet black. If you want the words "black", "gray", and "white" to have any meaning at all in an astronomical context, you have to define a range of albedos that correspond to these colors. Any reasonable range is not going to put an albedo of 20% as "white", because then most color neutral objects would be "white". Ice would be the same "color" as most rocks. That would be silly. In my experience, I have only ever seen things with very high albedos are called white.

So what? I'm sure white Labrador retrievers have an albedo of something like 0.3, but are actually called "yellow" labs. "Black" people are actually brown. Gray foxes are not actually gray, and they're not even in the Vulpes family (though they are closely related), so is even really correct to call them foxes? "Fisher cats" do not fish and are a species of marten, so they are as distantly related to cats as your dog is. Might as well call your cat a "flying weasel", it would be just as accurate. Want me to bring up more unrelated examples of poor naming?

You're taking a oft-stated fact about how long it takes energy from the core of the Sun to reach the surface far too literally. Photons produced in the core of the Sun never make it to the surface. Any source that says so is wrong. ENERGY produced in the core of the Sun takes millions of years to reach the surface. If the photons produced in the core of the Sun actually reached the surface, then the Sun would have the spectrum of a 16 million degree Celsius blackbody. We'd be bombarded by vast amounts of gamma rays and x-rays, and life on Earth could not exist. In fact, the Sun has a spectrum of a 6000 degree C blackbody, and its radiant power peaks in visible light, not x-rays or gamma rays. That's because all the photons we receive from the Sun originate on the surface, where it's relatively cool. What actually happens in the Sun is that photons produced in the core (a lot of gamma rays) get absorbed by solar material, heating that material. The solar material then emits new photon(s) at a different wavelength, a wavelength dependent on the solar material's temperature, according to Planck's Law. And also, just because the effective speed of light is slower through a medium (like glass) doesn't mean the photons are actually moving slower. The photons move at light speed between their interactions with atoms, and those interactions don't slow them down, they just absorb/re-emit them. Though really, it's overly complicated to use the particle behavior of light to understand how light propagates through refractive mediums, it's much better to look at it as a wave.

I disagree. The "colors" white, black, and gray are entirely determined by albedo. While the word "white" isn't exactly well-defined, generally, it's going to mean a high albedo, like, I donno, 75% or higher. Gray can in fact appear white, if you compare it to something very dark, like the night sky, but if it was compared to something that was truly white under the same illumination, its grayness would be immediately obvious.

I usually don't use sepatrons. I've tried and successfully gotten them to work before, but I actually found that my rockets always seem to survive being smacked by the ejected boosters, if they get hit at all. Until I have a problem, it's easier (though a bit less realistic, of course) to just not use them.

? An ice-capped cryovolcano? Something must be continuously producing the water vapor they've supposedly detected, because the gravity sure isn't strong enough to hold onto it. And I still disagree with you on whether these spots are grey or white. Remember, the 40% albedo measurement was taken before they resolved the spots. The reflected light was spread over a larger area than it actually subtends. So the reflectivity must in fact be much higher than 40%- so these spots are probably, in fact, "white".

Make the rover and the rocket the same thing. Duh. There's almost no justification for not making the rover and the lander the same thing, not when wheels are so lightweight. I can't understand why so few people to do this. It's by far better than making a separate detachable lander, except for like, Eve (where such a thing is impossible) and maybe Tylo (though I've made single stage lander/rovers for Tylo even), because you simplify your lander so much by doing so, and the lander and rover system becomes 100% reusable. ADDITIONALLY, your rover gains the ability to simply fly over impassible terrain, because except on Tylo, you'll have enough extra DV to make multiple landings. It's a win-win-win design. This is an old Duna rover I made a year back. It was capable of landing on Duna and returning to orbit all by itself. Oh and would also work on the Mun, Ike, etc. The lander in the screenshot was an over-designed (it was actually better than I needed) single stage to-ground-and-back-to-orbit Tylo/Kerbin lander, I was just testing it out on Duna.

Isn't there a fantastically small chance that entropy could actually run in reverse for some indefinite time? After all, isn't entropy at least mostly, or entirely, simply that "disordered" states are more common than "ordered" states, and once you have a huge number of particles, the chances of them progressing from order to disorder becomes, statistically, effectively certain? So the question is, if you waited an extremely long time, through random chance, could entropy reverse itself in a closed system? Like maybe you have to wait 10^100^100^100 years, but eventually, you could observe the entropy in a macroscopic system reverse itself- maybe you might see heat flow backwards (from cold to hot) for a few seconds?

You can implement a self-destruct on it too, for fun. I have a 10,400 ton stock rocket, and I rigged the abort button to fire a bunch of inward-firing sepatrons. The sepatrons cause key root parts to explode, making the rocket disintegrate in a very spectular and satisfying fashion. When I was a little kid, I used to build complicated Lego sets just to throw them off a balcony in my house and see how many parts they would break into... then rebuild them, and do it again. Funny, I'm 30 years old and now with KSP, I still find the same kind of thing satisfying