Wikipedia:Reference desk/Archives/Science/2016 September 4

= September 4 =

addiction
How do people get addicted to non-addictive things, for example an addiction to watching anime? — Preceding unsigned comment added by 200.52.200.10 (talk) 00:26, 4 September 2016 (UTC)


 * Behavioral addiction --Tagishsimon (talk) 00:29, 4 September 2016 (UTC)


 * "I used to be all messed up on drugs. Then I found the Lord. Now I'm all messed up on the Lord!" -- Cheech and Chong. ←Baseball Bugs What's up, Doc? carrots→ 00:37, 4 September 2016 (UTC)


 * "I believe in the Church of Baseball. I've tried all the major religions, and most of the minor ones. I've worshipped Buddha, Allah, Brahma, Vishnu, Siva, trees, mushrooms, and Isadora Duncan. I know things. For instance, there are 108 beads in a Catholic rosary and there are 108 stitches in a baseball. When I learned that, I gave Jesus a chance. But it just didn't work out between us. The Lord laid too much guilt on me. I prefer metaphysics to theology. You see, there's no guilt in baseball, and it's never boring, which makes it like sex... I've tried 'em all, I really have, and the only church that truly feeds the soul, day in, day out, is the Church of Baseball." --Annie Savoy in Bull Durham --69.159.61.86 (talk) 07:55, 6 September 2016 (UTC)
 * I would certainly dispute your classification of anime as non-addictive... Double sharp (talk) 12:56, 9 September 2016 (UTC)

Feynman Lectures. Lecture 20
Link: www.feynmanlectures.caltech.edu/I_20.html Can anybody explain, if we are trying to rotate wheel in such way to make axle vertical, then we put forces in vertical plane, not in horizontal. But according Feynman forces in horizontal plane appear. So who puts the forces actually?Username160611000000 (talk) 05:15, 4 September 2016 (UTC)

I think mentioned forces appear by themselves and when we resist them we apply another forces by our hands. Is it correct? — Preceding unsigned comment added by Username160611000000 (talk • contribs) 05:33, 4 September 2016 (UTC)
 * Convenience link - Rotation in space. See gyroscope, precession, and conservation of angular momentum.  The total angular momentum of the system (wheel + person + table) is conserved.  Initially, the angular momentum vector of the wheel is horizontal, so there's no vertical angular momentum.  When the axle is rotated, the angular momentum is transferred from the wheel to the table, so a torque is applied in the horizontal plane to rotate the table - if we ignore friction, the vertical angular momentum of the system will be the same (zero), but is now made up of equal and opposite components, one due to the rotation of the person and the table, and the other due to the wheel.  Your second statement is correct - the person's hands apply force to the wheel (in the vertical plane), which is transferred via the person's body and feet to the table, where the forces act in the horizontal plane. Tevildo (talk) 06:47, 4 September 2016 (UTC)


 * Feynman tries to explain the origin of forces. When we rotate wheel, we change L. So automatically must appear torque which can be replaced by forces F and -F. These forces appear not by us, but by themselves. If chair would be seized up we would feel these forces in hands. But if chair can freely rotate, we also feel forces, but can't resist and start rotating. E.g. we put wheel (fig. 20-2 ) at zero gravity and push one end of the axle up. In what direction will the wheel rotate? Username160611000000 (talk) 07:53, 4 September 2016 (UTC)
 * For the wheel in figure 20-2, gravity isn't relevant - the x-axis and z-axis can be in any direction, as long as they're perpendicular to each other and to the y-axis (defined by the axle). The wheel (and whatever is moving it) will rotate so that the net angular momentum about the x and z axes is zero.  Incidentally, if the chair in the first example can't rotate, the angular momentum doesn't disappear - instead, it's transferred from the wheel to the Earth, causing a (very small) movement in the Earth's axis. Tevildo (talk) 08:17, 4 September 2016 (UTC)


 * Still do not understand. Are F and -F on fig. 20-2 real? — Preceding unsigned comment added by Username160611000000 (talk • contribs) 09:18, 4 September 2016 (UTC)
 * Yes, these are real forces applied to the axle. There will be a corresponding reaction force in the person's arms - see Newton's Third Law.  Tevildo (talk) 09:29, 4 September 2016 (UTC)


 * Well, to be precise Feynman would have to draw 2 figures: on first he would have to show torque without F and -F, on 2-nd show forces without torque. But maybe torque itself is a replacement for something? Username160611000000 (talk) 10:02, 4 September 2016 (UTC)
 * I see your point - the rotation creates a torque, which produces a force on the structure that supports the axle. If the position of the support isn't defined, we can still calculate the torque, but not the force.  Tevildo (talk) 10:40, 4 September 2016 (UTC)

What means spherical angle sign ∢ on this summary for the lecture photo: http://www.feynmanlectures.caltech.edu/img/FLP_I/f20-00/f20-00.jpg (you need visit [www.feynmanlectures.caltech.edu/I_20.html page] first otherwise image will be forbidden)?? — Preceding unsigned comment added by 24.230.128.154 (talk) 14:50, 6 September 2016 (UTC)
 * "∢ Mm" is Feynman's abbreviation for "angular momentum", and "∢ vel" for "angular velocity". Tevildo (talk) 22:17, 6 September 2016 (UTC)

Naat and other genetic material identification tests
How do urine tests which detect genetic material work? Does it only detect it if in the urethra? Will it not detect if it's in the blood? 82.132.219.124 (talk) 12:27, 4 September 2016 (UTC)


 * The DNA is found in the cell nucleus - it doesn't matter where the cells come from as long as they have a nucleus (note that red blood cells don't). Urine is easier to obtain than blood, and always contains some cells (from the kidneys or from other parts of the urinary system). Wymspen (talk) 14:32, 4 September 2016 (UTC)
 * But what about Naat tests for bacteria, for example that entered through a cut somewhere or is in your lymphatic system? Wouldn't a urine test rely on the bacteria being somewhere in the urinary system?  Or is the bacteria or traces of it always likely to be in the urinary system regardless of when in your body is infected with it? 82.132.219.124 (talk) 17:33, 4 September 2016 (UTC)


 * Ref link: nucleic acid amplification test. Rojomoke (talk) 21:40, 4 September 2016 (UTC)
 * I've seen the article but it doesn't really answer my question. 82.13.100.15 (talk) 16:55, 5 September 2016 (UTC)

Pressure filtration
What types of filters are used in industry for filtration at pressures of 300-1000 psig? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 21:09, 4 September 2016 (UTC)
 * What fluid? Air, water, oil? Tevildo (talk) 21:24, 4 September 2016 (UTC)
 * Water or other aqueous media. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 22:32, 4 September 2016 (UTC)
 * For water at that sort of pressure, we're in the Reverse osmosis region. Filters for this application are usually of the Thin-film composite membrane type, made from polyamide and polysulfone components. Tevildo (talk) 23:47, 4 September 2016 (UTC)
 * And for more coarse particles? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:53, 5 September 2016 (UTC)
 * Microfiltration, Ultrafiltration, and Nanofiltration are used to remove larger particles - these processes take place at lower pressures than reverse osmosis. This manufacturer's brochure has a useful summary. Tevildo (talk) 09:56, 5 September 2016 (UTC)
 * Thanks! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 01:22, 6 September 2016 (UTC)