MDJH

Today I noticed a "chained pen" (assuming that's what it called; though the "chain" was a series of metal beads connected by an apparently-metal string) with the pen and chain removed from its holder but still connected to each other. I then proceeded to pick it up and, while holding the pen, spin around the "chain" in a circular motion. (Sort of like a standing wave, except instead of up and down it goes around and around... heh, that rhymes.) I noticed that the faster I spun the "chain" the more of a "pull" it felt like there was on the pen... anyone here know what this is?

So were the probes that found the acid passivated beforehand? If so, does that suggest that they suspected it was sulfuric acid before they even sent the probes?

I often hear about how driving more slowly is supposed to save on fuel emissions. Are those who say so referring to "less fuel use per unit of time on the road" or do they mean over time as well? If so, why?

According to Carl Sagan's "heaven and hell" documentary, Venus has clouds made of concentrated sulfuric acid. Wouldn't that react with the metal in the spacecrafts they used for exploring Venus?

So if the algae is grown in deserts... that means it's getting its energy from the sun, right? Why is that more practical than direct solar power?

... I just realized that if a plastic bottle is spinning around in a circle with one end always pointed at the centre, then that end would be moving at a different speed than the other end... am I correct in assuming this? Also, how do you find the speed at one end from the speed at the other end?

What do you mean?

1. Car battery charger? Where could I get one? 2. Inert anode? Like graphite?

Not sure if here or another board would be a better place for this topic but whatever. One popular argument against nuclear power is the possible risk of a nuclear meltdown makes it dangerous, no matter how less and less likely a nuclear accident gets as technology improves, because IF such an accident were to happen, the results would be disastrous. Well, IF such people supported fossil fuels, recent events show their point to be quite moot. But on other forums, I've found that those who actually address this tend NOT to be in favour of fossil fuels, but instead tend to be in favour of wind and/or solar power; which begs the question; how feasible are wind and solar? I've heard many arguments for and against them, and I find it hard to tell who to believe. Some of the arguments I've heard on this subject are questionable at best; the argument that "we need power when the sun is down" obviously doesn't address that we could STORE the energy when it's sunny, and USE the energy when it isn't; in that case, it's a matter of whether or not the AVERAGE power the sun would provide would be more than the AVERAGE power people use. Same for wind; obviously we shouldn't rely on the wind blowing all the time, but on wind power accumulating energy over time. But then again, the case against wind and solar doesn't necessarily rely on such arguments. The question is, how feasible are wind and solar, and why or why wouldn't they be feasible?

I know I've asked about this before, but I was thinking of how to do water electrolysis in a reasonably efficient and/or relatively inexpensive manner. One idea I had was to set up a bucket, throw in some epsom salt (my current bag of epsom salt doesn't specify whether it's the heptahydrate or some other concentration of it though) and add tap water and stir until it's either all or mostly dissolved. Then I'd put in a couple plastic or glass bottles, (one about twice the size of the other) immerse them in the solution until they are filled, then find some way to fasten them upside-down (ie. the open end is facing downwards) and have electrodes set up so as to be insulated outside the bucket, on its way into the bucket, and just about everywhere except either inside the bottles or just below such bottles (preferably the latter, so long as the bubbles would go into the container, since I'd like both bottles to be filled with their respective gases) and connect said electrodes to a power supply that would consist of a combination of AA and AAA batteries connected primarily in parallel, through means of one piece of aluminum foil across all their positive terminals, and another piece of aluminum foil across all their negative terminals. This raises a few questions: 1. How long would it take epsom salt to either reach saturation or get fairly close to it? I ask this because with an unspecified concentration, I wouldn't know how concentrated the epsom salt would be until I brought it to near saturation through stirring, but I wouldn't want to assume too soon that the epsom salt was saturated. 2. A related question, how much voltage does it take to drive electrolysis with epsom salt as the electrolyte, and to what extent does it depend on the concentration? 3. And related to question 2, how would the current be drawn if the batteries are connected in parallel? Would it draw a variety of voltages (ie. from varied effectiveness of the batteries) or would they average out? Would the current be drawn as if each battery-water-battery loop were its own circuit, or as if the combination of batteries were an average power source and the water was the resistor?

What about trees? Would it be worthwhile to make ethanol from them?

I'm not asking for help with homework, (well, not directly anyway) though I can understand why you got that impression. I did introductory physics courses during my first year of university, (didn't learn that thoroughly though) as well as a few more physics courses since, (again, didn't learn it very thoroughly) but I've been unsure about what to major in for a while and have been meandering with all kinds of introductory courses for subjects other than physics; but I've been considering returning to a physics major, and was just trying to refresh my memory on this kind of stuff, thus I'm going through my first year physics book looking for whatever things I don't get, or am not sure if I get, so as to check my understanding.

Well, should I assume that gravitational potential energy and macroscopic kinetic energy are the only forms of energy involved in this case? If so they'd have to land at the same speed, but I'm wondering if there's something I'm missing...

But would the average pressure inside the container be greater than the average pressure outside the container? Let's say it was a small radius (ie. the bottle was about 20cm long, and the opening was about 2cm away from the centre of rotation) and a very fast speed (let's say a hundred metres per second) and this therefore created centripetal accelerations ranging from 45454m/s/s to 500000m/s/s; would the pressure in the bottle be significantly higher than external pressure?

Treating air resistance as negligible for this case, suppose we have three objects thrown FROM one vertical position TO another vertical position; the initial and final vertical positions being the same for each object. They are thrown at the same speeds, but at different velocities; one is thrown at an upward angle, one is thrown at a downward angle, and one is thrown horizontally. Would they have the same speeds, or different speeds, upon hitting the ground?

One major criticism of the use of ethanol as a fuel source is that it's "made from corn" and that switching to ethanol would raise corn prices. But what about hemp? According to , ethanol could be made from hemp as well. If that's true, then shouldn't they be using that instead?

What if it were a plastic bottle with the cap open, would this pressure gradient suck air in from the surroundings?

Yeah, I've heard of "centrifuges" before; our chemistry labs used them to settle insoluble precipitates. I just wasn't sure if the idea of a centrifuge was applied to gases, and I guess it turns out it is. Also, if someone were spinning some container (let's say a plastic bottle) that had one solvent substances on the "outer" end and a solute gas on the "inner" end (let's say filled with carbon dioxide to dissolve in water) would the centrifuge's pressure gradient force more CO2 to dissolve in the water?

Ah ok. So it's in units of angle per units of time, rather than in full circles per time... though I suppose "full circle" would qualify as a unit of angle anyway right? As if "full circle" were a unit of angle measure equivalent to 2pi radians? Also, what about my pressure gradient question?

Ok, another question. Would the current through the load be pulled through as if each battery-to-load-and-back loop were its own circuit?

I was recently thinking about centripetal acceleration (a=vv/r) and I have a few questions about it... 1. Since gravity's variation with depth has a corresponding air pressure variation with elevation, I was wondering if spinning an enclosed container (with air in it) around in a circle such that the same part of it was always facing the centre (ie. similar to how the same face of the moon is always pointed towards the Earth) then if the stronger forces towards the circle's centre (ie. where the radius is closer) would push air enough to the part of the container further from the centre to create a pressure gradient within the container, in addition to whatever pressure gradient already would exist for height. 2. I was thinking about how to find centripetal acceleration as a function of frequency of circling, since speed would be difficult to directly measure. So I thought of the following formulae, where Circ means circumference, T means period of oscillation (as in, seconds for the object to go full circle) Circ = 2*pi*r v_circ = Circ / T T = 1 / f Therefore v = 2*pi*r*f ... and in turn... a = (2*pi*r*f) * (2*pi*r*f) / r a = 4 * (pi*pi) * r * (f*f) Thus my derived formula suggests that acceleration is proportional to the radius, and proportional to the square of the frequency with which the object is rotated (as in, how many times it is spun full circle per second) with the coefficient being the product of 4 and the square of pi. Are there any problems with my methods and/or results?

If I had a combination of several AA and/or AAA batteries, and I had some sort of conductor (let's say a piece of aluminum foil) over all their positive terminals, and another conductor over all their negative terminals, then had some piece of wire go from one conductor, through a load, (like a voltmeter) to the other, would this function as batteries connected in series, or as batteries connected in parallel?

According to Wikipedia, iron is above hydrogen on the activity series. Would hydrochloric acid attack steel, or would the carbon hold the reaction back? Ah, so nitric's corrosiveness has more to do with its anion than its hydronium... would the same apply to other nitrate salts, or does the hydronium still have to be present for such reactions to work? "Oxidized" as in given an oxide compound, or "oxidized" as in loses electrons? And where does the third oxygen atom in the nitrate ion go? So would this mean that a can made of "aluminum" is actually aluminum oxide on the outer surface? Merged post follows: Consecutive posts mergedAnd another thing, what about bases? I've heard that aqeuous sodium hydroxide reacts with aluminum to form hydrogen gas, how do reactions between metals and strong bases work?

One thing about acids that caught my attention back in high school chemistry was that they reacted chemically with metals to form hydrogen gas. Since then, I haven't done much of this in high school or college chemistry labs, but I've looked at youtube chemistry videos too, and found some things about acids and metals slightly confusing. For example, according to , aluminum is resistant to nitric acid; yet copper isn't. Hydrochloric acid, on the other hand, supposedly doesn't react with copper but does react with aluminum. Another thing is how strong bases react with metals too, such as how sodium hydroxide supposedly reacts with aluminum to form hydrogen; so hydrochloric acid and sodium hydroxide placed in separate aluminum containers would react with the containers, but mixing them beforehand would give sodium chloride, which supposedly wouldn't react with the containers? Is there any chart saying which acids and bases react with which metals? Or any way otherwise of finding out whether or not a given acid or base would react with a given metal?

Ah, sort of like with galvanic cells or electrochemical cells. Got it.