dirtyamerica

We don't want to confuse weight with mass. Sure, the spoilers pushing down on the car would make it weigh more on a scale but the mass of the car stays the same (besides the burning of the fuel, tire wear, etc.) A car with so much mass will have so much inertia, preventing acceleration, no matter how much it is pushing down on the ground. Imagine a bowling ball hanging by a helium balloon. It weighs nothing but will still be difficult to push because it's still made up of more and denser "stuff" (atoms). Or a balloon and a bowling ball inside a space station. Both have zero weight but trying to move the bowling ball will still be more difficult. Weight is a function of gravity (or the downforce of wind). Mass is a function of the amount of elementary particles that the object is made of.

To get 1 gallon of clean water (or "permeate") it will require 1.33 gallons of "feed" water. Typical reverse osmosis units run at a 75% recovery rate (or how much clean water you make). You need a certain amount of water going to waste (called concentrate) to remove the impurities that are left behind. A proper set-up like this will also prevent the membranes from scaling up. ROs are more effective if you are using water that has already been clarified, filtered and degasified.

IIRC, Earth was closer to the sun about 8 months ago than now during its perihelion.

and don't forget to add the acid SLOWLY, not all at once!

or pH paper. Check your local hardware store for swimming pool supplies. They may have a pH test kit.

sound waves also refract

I agree as I work with it frequently (water treatment). The essence of the hand-warmer I once read about and mostly forgot was that a CaO packet is sealed from the atmosphere in its packaging. Once you open the wrapper and knead the warmer the oxygen reacts to the Cao, releasing heat. The calcium hydroxide doesn't leak out of the package because (I forget).. I'm not too helpful but I tried!

I remember reading somewhere about hand warmers made with calcium oxide. ( http://en.wikipedia.org/wiki/Calcium_oxide ) Maybe the above link will help. be safe

copper ions work too

The best way to teach Science is hands-on, whether through lab work or just good old concrete examples. You can drone on about theories but once you give students something tangable to work with it's like magic. I used to teach sciences in a middle school. Fortunately at that level you can stay away from huge equations that might scare some kids. My philosophy was to trick them into liking Science by distracting them with cool stuff. hehe Students learn more by doing Science and applying higher level thinking skills (analyzing, infering, etc), not just by seeing or hearing it.

interesting concept. I've noticed that on some color-coded periodic tables they don't assign H a color.

There is a temperature gradient. It's the why weather stations' thermometers are placed at a standardized height of 4 or 5 feet off the ground.

I haven't read all the way through this thread so forgive me if I'm posting something that's already been said! Science should always be approached in a skeptical perspective, but at the same time, maintaining a "hopeful" one. Nothing in science is a given unless it's a law, up until it's proven...anything is possible. My philosophy on religion and science is that you cannot use either of these to argue, say for example, "how we got here". That's an argument using apples and oranges. They are two totally different trains of thought. So a theologist debating existence (for example) with a scientist is a waste of time because neither persons' ideas can absolutely, without a doubt, be proven. My answer to your question: NO. Whether you're a religious person or not, as a scientist, you shouldn't discount all that is possible. Flat-out believing in everything that was written in the Bible (example) and trusting those who authored it, is the same scenario as being a scientist who is an atheist. Personally, I think that science is a way of proving how God works (via laws, theories and facts), which supports some of what was written in the Good Book (discounting what was surely written out of current societal norms and other cultural "spiciness"). I'm thankful that God has given me the patience and intellect through what we call science to learn about the wonderful gift of this universe and the life He gave us.

also if they have a higher vapor pressure

I once read that it has something to do with how your brain processes events in early childhood..and once these cause/effect relationships are established, they stay with you for life. in my personal experience of this phenomenon (realized at or before kindergarten): for single digit numbers: odds = wet evens = dry anyone else have this? Other than that I have certain chapters of my life that associate with certain feelings or "thought smells" but I can't quite pin a sense to it.

I think that Hawking is still mentally very spry. IMO, "plausible" means: under the proper theoretical conditions, things could happen...although maybe very rare. But yeah, we should be cautious of aliens and their motives (if they exist). We can't even voyage to another planet right now. If they have the technical know-how to come all the way here (perhaps using the distance connotation loosely) then surely they've also built a better mousetrap too. The bigger picture here: I think Hawking continues to think like a scientist: You have to remain skeptical until it can be scientifically proven, without pruning your ideas of what is possible.

OK, wait, so you're asking "how much would the ball appear to weigh based on the force exerted on the scale" forgetting about the spring and all that. Basically, "how much force is the ball hitting the scale with?" So, I'm still agreeing with my previous post, kind of... no matter what happens after it hits the surface of the scale. I hope this is correct but what about velocity = 1/2 x acceleration due to gravity x time squared? Please somebody correct me here if I'm wrong! I thing that F=ma can be used and then F (in Newtons) can be converted into pounds. But you first have to find what the speed of the mass is from a 13ft drop. Basically, I'm converting my thoughts into words here even though it doesn't help. I could go pull out my physics book from my library but I don't want to do all the work for ya (apologies!).

Oh OK, because I was going to say that you answered your own question inside the question (wood comes from trees) LOL! Interesting question though. I'd suggest maybe getting in touch with a university renowned for plant sciences and asking them for some info.

bodies (including planets) that form into a spin do so because of the Coriolis effect. IIRC, only one or two of our planets have a retrograde spin, probably caused by some catastrophic event.

aka permanent magnets

I'm just guessing here but if you're looking for economy, using a cheap air filter will probably be more cost effective than building and paying for the electricity to run an ESP in your house. I can only speak about ESP's based on my knowledge/experience of this application in the industrial setting where huge amounts of airflow would seriously be disrupted by a filter...along with other logistics. Essentially, an ESP contains two types of plates: Discharge Electrodes, which give a charge to the airborne particulates and Collecting Electrodes, which attract the particulates via an oppositely charged static electrical force. The amperage through all of these electrodes are comparitively small compared to the voltage (read: static electricity). Once the particulates are collected on the proper electrode plates, they can be "rapped" off by automated hammers. The clumps of particulates fall to collection hoppers and are disposed of by other systems. I've seen a commercial on tv once about a small, home unit that does the same thing except you have to turn it off and wipe the collecting electrodes off with a rag every so often. I guess if you really wanted to impress your visitors you could follow an ESP up with a wet scrubber system, lol.

what if we assume that the scale has no "spring" to it? He could convert the weight of the 10lb ball into mass. Then calculate the velocity it reaches from 13 feet high (probably converted to meters/sec)....and then what resulting force it would put on the scale. I don't remember the equations from physics so I can't really help beyond this. The answer to the question doesn't seem as simple as F=ma.

electricity

ah, thanks for the link. I guess I didn't do the right search at wiki.. I was under the impression that urea was a waste protein in bio processes...but now I realize how simple the molecule is. I didn't know that urea is in sweat. Interesting. Now I can really freak my wife out next time she kisses my cheek and I'm sweaty from yardwork. heh

lots of long posts here (well, ok, 2) so forgive me it this is repeated in all that text.. Another example of coherent thought is when lions hunt. They use teamwork and have a specific pattern not unlike a football team. It's not just "run and chase after whatever is closest" but instead well planned.