Wikipedia:Reference desk/Archives/Science/2009 April 18

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April 18

Coriolis force on a river in the northern hemisphere

"A straight river flows with speed v in a direction α degrees East of North. Show that the effect of the Coriolis force is to undermine the right bank. Does the magnitude of the effect depend on α?"

My brain has shut off, I don't even know where to start! Thanks for any help,

Mathmos6 (talk) 00:15, 18 April 2009 (UTC)

This seem's to be a homework. Is that the case? I hope it isn't because the statement "the effect of the Coriolis force is to undermine the right bank." is actually incorrect. Dauto (talk) 01:01, 18 April 2009 (UTC)

WP:DYOH Smartse (talk) 01:16, 18 April 2009 (UTC)

Oh dear, it is part of my set work, yes! Perhaps that explains why I've spent so long trying to understand why and getting nowhere - what does happen then? I've read through the wiki article on the effect but I'm still not completely certain, gah! Mathmos6 (talk) 01:41, 18 April 2009 (UTC)

I think it should be true in the northern hemisphere. The rotation of the earth about its axis gives the water angular momentum. As the water moves north, it gets closer to the axis, so conservation of angular momentum means it tries to rotate more rapidly about the axis, like an ice skater drawing in her arms to spin -- this pushes it against the right bank. Looie496 (talk) 01:51, 18 April 2009 (UTC)

Okay, so assuming this is talking about the northern hemisphere, does the angle east of north affect the magnitude? Or equivalently, I suppose, will you have a different effect if the magnitude of α is 0/90 degrees? You should have no effect along the hemisphere and 100% of the effect northwards, right? Mathmos6 (talk) 01:58, 18 April 2009 (UTC)

The effect doesn't depend on the angle $\alpha$. The coriolis force will indeed push the water rightward. The problem with the statement is that this rightward push will very lightly raise the water level on the rightside but that does not undermine the riverbank. To undermine the riverbank you would need an effect that speeds up the flow of the river on its right side. Coriolis effect doesn't do that. Dauto (talk) 02:10, 18 April 2009 (UTC)

Actually, a flowing river, being a fluid, would also be deflected rightwards as it flows. I am not certain the effect would be great enough to cause undermining of the river bank, but it may do things in the large scale like cause subtle differences in the overall way rivers flow across open plains and the like... --Jayron32.talk.contribs 21:31, 18 April 2009 (UTC)

The effect makes the river level rise slightly on its right side. That doesn't undermine the river bank. Dauto (talk) 19:51, 19 April 2009 (UTC)

Recycling efficiency - plastics vs steel

Plastics & steel are 2 key components of modern industry. Both can be recycled, both *are* widely recycled. I'm wondering which is more "efficient" ?

I place that word in quotes because I can think of two methods of comparison (and perhaps you can think of more?):

Resource cost to recycle 1 ton of product into raw materials for plastic vs steel

OR

Recycling cost : original manufacturing cost ratio for plastics vs steel

What do you think? 61.189.63.224 (talk) 05:17, 18 April 2009 (UTC)

I'll try a qualitative answer here: steel is more efficient to recycle overall. I base this statement on the fact that steel is more widely recycled.

One factor in this is that it's more easy to collect and sort the steel. Crushing a car is easier than sorting six million pieces of plastic, and a bridge or a ship can pretty much be just thrown into a mini-mill. Plastics come in a wide variety of types (look at the number inside the recycling symbol on plastics, it goes up to at least nine) and are difficult to segregate since they need humans or spectroscopic/laser methods to sort. Steels by contrast can be sorted by weight and magnetic properties.

Another factor is that steel is much more dense than plastic. This comes into play when considering the cost of transporting the material back to the recycling facility, since steel "weighs out" before it "cubes out". This means that the trucks/trains/ships are carrying their maximum load, which is usually more fuel-efficient. Put another way, you probably need fewer trucks to ship the equivalent amounts of steel and plastic for their strength-weight-volume ratios.

And steel has the big advantage in thermodynamics that you just have to remelt it, you don't have to reform the molecular structure. With steel, you just make a melt, check its properties, then throw in a little more of what you need to get the exact metal alloy you're trying to produce. With plastics, you have to deal with thermal dissociation of the plastic molecules and more severe negative properties of the contaminants. Steelmaking is a metallurgical process, plastic is a chemical process.

As I said, those are qualitative impressions. If you had a million steel computer cases sitting beside a million plastic cases just outside your recycling facility, I'm not sure which one would win. I'd put my money on the steel though. The economics of recycling are very complex. But since people will come over to your house and tow your old car away for free, whereas they won't come over to get your plastic bags for free - again I'm betting on steel. Franamax (talk) 23:16, 18 April 2009 (UTC)

Recycling economics is complex; the deciding factor however in determining if it is economically feasible to recycle a material is in having uses FOR the recycled material. Take rubber tires as an example. They are a complete nuisance as a waste product (take up a lot of space, never degrade, etc. etc.) and so should be an ideal candidate for recycling them. However, they are completely worthless in that regard, as there are so few uses for recycled tire rubber. There are a few weird esoteric uses, such as paving running tracks and things like that, but really you can't even use it to make new tires out of, its a worthless material, so there is really no good reason to recycle it. The chemistry of plastics is similar. With steel cans, you melt down the steel cans and make more steel cans. Its simple and easy and means that you will always have enough demand to make steel recycling economically feasible. With plastics, it just doesn't work that way. You can't melt down plastic milk jugs and make more plastic milk jugs; the chemistry just does not support that sort of application. Sometimes, you can use the recycled plastics for alternate applications, but like with the rubber tires example, the demand created by these alternate applications is just not enough to make it as econimical as metal recycling. --Jayron32.talk.contribs 04:56, 19 April 2009 (UTC)

I thought they fed milk jugs back to the cows who made them! And I'm pretty sure we ship all our old tires to Springfield, that fire's been burning for 20 years now. :) Franamax (talk) 20:13, 19 April 2009 (UTC)

Power production from sea water by electrolysis process.

Would it be efficient to seperate hydrogen from sea-water by electrolysis process and then to produce electrocity by using the hydrogen in a gas turbine? —Preceding unsigned comment added by Shamiul (talk • contribs) 07:59, 18 April 2009 (UTC)

No. See First law of thermodynamics for why you cannot win, and Second law of thermodynamics for why you cannot break even. Splitting a water molecule requires exactly the same amount of energy that is returned when you recombine it. But none of the processes are 100% efficient - i.e. you lose energy. As a rough ballpark figure, in you configuration I would expect the loss to be around 60%. --Stephan Schulz (talk) 08:46, 18 April 2009 (UTC)

Certainly that isn't going to work in terms of getting free energy (but then there is no possible way to get free energy - period - because of the laws of thermodynamics). But there may be reasons to do it anyway. For example - it's proving very difficult to design batteries to make electric cars a particularly viable option - so using the electricity to make hydrogen and putting the hydrogen into the car makes some sort of sense. Also, if you were to supply power from wind turbines or nuclear power exclusively - then there would be times of day when you'd be producing more electricity than you need - and turning that energy into hydrogen, which you'd store and burn later when the need for electricity is higher. So there are reasons to do it - but none of them relate to getting energy for free - which is completely impossible by any means. I think Stephan's estimate of a 60% loss is an under-estimate. There aren't many gas turbines that are more than 60% efficient - and electrolysis is at best only about 80% - there are bound to be other losses. I'd be surprised if you got back 40% of what you put in. Probably, a gas turbine would be a bad way to get electricity from hydrogen - hydrogen fuel cells seem like a better bet. SteveBaker (talk) 20:02, 19 April 2009 (UTC)

Sleep

Last night, I had approximately five hours of sleep and not suprisingly, I am unable to think about mathematics today. Similarly, with regards to learning vocabulary (from another language), my short term memory did not seem to be up to its uaual standard. I also seem to be consistently thinking about sleep the whole day, unable to do much. I have thoroughly read the article on sleep but could not find the answer to this question - thinking in which areas of mathematics is affected most by a lack of sleep (and which areas are affected the least) and which aspects of thinking in general, are affected by a lack of sleep? I think this reference desk is the best place to post but hopefully I will get answers from the Wikipedians at the other reference desks. Also forgive any errors in my writing. :) --PST 10:55, 18 April 2009 (UTC)

Have you read Sleep deprivation? I wouldn't expect getting only 5 hours sleep for one night to have a significant effect, though. Plenty of people sleep that little routinely (studies vary in their conclusions about whether that is a good idea or not). I expect your problem is not that you are too tired, but rather that you are too sleepy. You need to do something to wake yourself up - I find sugar and light exercise to be the best way to do that. Once you've woken up and got going, you should be fine. --Tango (talk) 12:49, 18 April 2009 (UTC)

Thanks for your advice and comments. The other question I have is about sleeping too much. If I were to sleep in, although having slept for 10-12 hours, I feel sleepy 2 hours after having woken up. Describing it as sleepy might be inaccurate - rather it is a temporary drowsy sensation. Is it better for thinking, to sleep for around 10-12 hours or more, or a moderate amount? For me, it is usually around 8-10 hours of sleep that is the best for logical thinking. --PST 14:27, 18 April 2009 (UTC)

I know what you mean - I find sleeping too long leaves me kind of fuzzy. Again, exercise seems to help (just 10 minutes brisk walk in the fresh air is often enough). I think a typical amount of time to sleep is 6-8 hours, although opinions vary on what is best (I remember a study that showed people that sleep an average of 6 hours a night live longer than those than sleep 8, which is the opposite of conventional wisdom). --Tango (talk) 14:59, 18 April 2009 (UTC)

Having a short (20 minute) midday nap can help immensely if you aren't sleeping enough at night. Our article Sleep is full of useful advice and data. SteveBaker (talk) 19:52, 19 April 2009 (UTC)

I agree - it's amazing how much better I feel after a short nap when I haven't been sleeping properly. However, it seems from the OP's question that the lack of sleep was a one-off, so hopefully they slept properly the next night and all is well now. --Tango (talk) 21:58, 19 April 2009 (UTC)

These seem like the symptoms of caffeine addiction to me. Give up tea and coffee and you will feel alert all the time, and go to sleep quickly and wake up alert and refreshed. The few days or weeks after giving up caffeine will not be so good. 78.147.2.142 (talk) 11:29, 22 April 2009 (UTC)

hiv transmission

can hiv be transmitted through kissing?

and

which is more likey a way of hiv transmission, swallowing cum or bareback sex?

 —Preceding unsigned comment added by 71.198.192.120 (talk) 14:57, 18 April 2009 (UTC) 

I believe HIV can be transmitted through kissing, but it is quite unlikely. Cuts, sores, bleeding gums, etc. can increase the risk, though. Unprotected vaginal or anal sex is almost certainly a greater risk than oral sex, although cuts, sores and bleeding gums do, again, increase the risk. I remember an excellent table being linked to in a previous ref desk question showing the risks of various sexually transmitted infections being transmitted is different ways. I'll try and find it. --Tango (talk) 15:04, 18 April 2009 (UTC)

Found it. It doesn't specify its source, though, so no guarantee of accuracy. --Tango (talk) 15:07, 18 April 2009 (UTC)

The only was HIV could be transmitted through kissing if the receiver has some form of cut in their digestive tract before the stomach. If not, the virus will be broken down in the stomach. It's pretty rare to catch HIV this way.

As for your second question, the former could only result in transmission if the above provision still applies. The latter, however, is much more likely as anal sex is, quite frankly, done in an area not designed for such activities and can result in more cuts within the anal canal. If semen enters a cut, it can transmit the virus to the other person. Regards, --—Cyclonenim | Chat  16:06, 18 April 2009 (UTC)

Unprotected oral sex is NOT safe sex. There's plenty of HIV-susceptible tissue in the tonsils. The exceedingly low risk of mouth-to-mouth kissing (see page 3 of the PDF) is probably related to how unlikely it is that saliva will contain infectious HIV. --Scray (talk) 16:22, 18 April 2009 (UTC)

There have not been any documented cases of HIV transmission by French kissing. This paper discusses reasons for the low HIV content in saliva. Despite this, the CDC cautions against French kissing with HIV positive people due to theoretical risk of transmission. Axl ¤ [Talk] 16:56, 18 April 2009 (UTC)

There is also a chart detailing the chances of contracting HIV (and eventually AIDS) from various sexual and non-sexual activities at AIDS#Prevention. ~AH1^(TCU) 01:04, 21 April 2009 (UTC)

Figuring out when a star does heliacal rising

Hello Science Deskers! (a) If I know the right acension and declination of any star, how do I do the calculation to figure out when that star has its heliacal rising? (I'm hoping there is a way to do some math and get an answer such as "19 days after the summer solstice", that kind of thing.) (b) Once I figure out the answer, how would I adjust it to figure out when that star would have had its helical rising for any year in the past (such as 5 or 10 or 15 thousand years ago)? Thank you, WikiJedits (talk) 16:00, 18 April 2009 (UTC)

What you need is a planisphere. Make sure you get one that is for the latitude where you live. You can also get free ones off the internet you can print yourself or software you can run, just try googling for it. If you want to do the trigonometry yourself, you will need a book, this one iss very old (1834) but because it is out of copyright you can view it online or print it out. I don't think trigonometry has changed much since then. SpinningSpark 17:12, 18 April 2009 (UTC)

Thank you SpinningSpark. I have found a planisphere but can't figure out how to read a heliacal rising from it. For example, I put Spica over where it says Eastern Horizon, but the earliest time it gives is 5 am and the month over there is November. I know sunrise is way after 5 am in November. Is there a way to work it out by doing a calculation instead? I have looked at the book but it is way beyond me. Is there a method a beginner could use? (Also, do you or anyone else know the answer to my question b?) Thanks again, WikiJedits (talk) 01:52, 19 April 2009 (UTC)

My Planisphere is the Philips' one like the picture in the article so if you look at that you will understand what I am talking about. You are right that the first step is to put Spica on the Eastern horizon. The moving part of the planisphere has a time scale, and the fixed part has a calendar. At any particular date, this will tell you the time Spica will rise. If you look for 19th April, you will find that Spica is rising at about 7pm in the Northern hemisphere. This depends on your latitude which is why it is important to get a planisphere for your own location. Ok, so 7pm tells you that Spica is rising in the night sky (or before) at the moment and is nowhere near its heliacal rising. Next you look around the scale till you find a date at which the timescale is showing the time of sunrise for that date (again dependant on your location). 6am is at 30th October on the planisphere, so if sunrise is at 6am on that date, then that is the also the heliacal rising of Spica.

If you cannot deal with the trigonometry in that book, then you are not going to be able to do the calcualtion by hand. I suggest you get some software to do it for you, or else go and learn the maths first.

For 5 or 10 years in the past, there is virtually no difference to the date of the heliacal rising. For thousands of years in the past, you must take into account the precession of the earth. To do this you must first locate the position of the North Celestial Pole in the epoch which you are interested in. You can get that from this diagram. Next, you must move the pivot point of your planisphere to the location of the ancient North Celestial Pole (don't destroy your good one, print a throwaway one off the internet). Then you just proceed as before.

Hope that's all you needed to know. SpinningSpark 10:07, 19 April 2009 (UTC)

Thank you, I really appreciate the time you've taken. Think I get it now - I need a table of sunrise times and to compare it to the times and dates shown on the planisphere. Got one off timeanddate.com and doing that for Spica again (at 30N) gives me a best match with October 17, 5:58 am. Additional question 1 - the heliacal rising isn't exactly at sunrise, is it? Do I need to allow extra time? Would it be better to pick July 3 when sunrise is at 4:58 am? Cos that's quite a difference.

Additional question 2 - About the past calculation, I must be doing something wrong? I drew the north celestial pole circle on the rotating part of the planisphere and put the pin in a different place along the circle. But this didn't seem to make much difference (other than the planisphere not fitting together so well). For example, I tried it for halfway around the circle, or about 10,000 years ago, and putting Spica on the eastern horizon still has the fall months aligning with the morning times, when I would expect it to be the spring months. Do you know what I'm missing? Much thanks for all your help, WikiJedits (talk) 19:42, 19 April 2009 (UTC)

Turning radius of a vehicle

The turning radii of all four or more wheels of a vehicle are always different.What does the mean turning radius given in their specification mean? —Preceding unsigned comment added by 202.70.64.16 (talk) 17:10, 18 April 2009 (UTC)

Mean turning radius is the radius through which the centre-line of the vehicle turns. It is usually defined at the front wheels, the mean radius is different along the length of the vehicle in general. SpinningSpark 17:38, 18 April 2009 (UTC)

Car manufacturers sometimes talk about the "turning circle" which is the smallest circle within which the car can do a complete 360 turn...that's a more useful measure - and refers not to the wheels but to the parts of the vehicle that stick out the most. For a car that has lots of "stuff" sticking out behind the rear wheels (like a US-style school bus), that can be a significantly larger number than the radii of the circles made by the wheels. For my car, the number in the handbook specifically excludes the door mirrors! SteveBaker (talk) 19:46, 19 April 2009 (UTC)

You probably won't be surprised to hear there are several different definitions. One useful one is the kerb to kerb diameter, ie effectively the narrowest road you can turn round in. The wall wall diameter is often used in Germany, I think it is a DIN standard. The Japanese use something else again. Greglocock (talk) 10:22, 22 April 2009 (UTC)

Sedimentary rock, evaporites: How does gypsum end forming a stratum .50m thick?

Where can I learn about the processes by which gypsum -probably originally sedimented in the form of thin little crystals- end up forming strata half a meter thick and spanning kms?

This question applies (in my curiosity) to all kind of evaporites.

In the articles about evaporites and sedimentary rocks, and in the books I've read, I don't see anything explaining the processes that undergo the evaporites once sedimented. Jorgemelis (talk) 17:17, 18 April 2009 (UTC)

See Dead Sea#Natural history. SpinningSpark 17:51, 18 April 2009 (UTC)

See also Sabkha (a supratidal salt flat), which is an environment in which thick gypsum deposits are often formed, sometimes in the form of desert roses. Evaporation at the land surface causes the rise of brines by capillary action and as these evaporate they deposit salt at the surface and gypsum and aragonite in the subsurface. In deeper water areas gypsum layers may be formed by crystallization at the air-water interface followed by sinking of the crystals to the bottom. Mikenorton (talk) 19:31, 18 April 2009 (UTC)

Lazy smokers

Which of these would improve the overall health of an inactive (no exercise) smoker with a typically bad, high-fat diet more?

• Stop smoking
• Regular exercise
• Improved diet

Cheers. As before, if it's considered a medical advice issue, I have no problem with it being taken down. Vimescarrot (talk) 19:59, 18 April 2009 (UTC)

I doubt there is an answer that applies in all cases. People have lived to be over 100 while smoking 20 a day, so stopping smoking won't necessary improve anything at all (although it most likely will). Exercise and diet are complicated things, there aren't simply "good diet" and "bad diet", "exercise" and "no exercise", so more information would be required. Also, it's necessary to know in what way the person is unhealthy - if they are suffering from Emphysema, stopping smoking will almost certainly improve their health more than the other two, for example. --Tango (talk) 20:26, 18 April 2009 (UTC)

I wondered if I might get that. Since I'm just curious in general, not looking at anyone or any particular set of circumstances in particular, I probably can't get a real answer as such - though anyone is welcome to come in with more input and opinions. Vimescarrot (talk) 20:37, 18 April 2009 (UTC)

Of course, health is highly individualized. One can speak in general terms for what works in averages, but you will always find anecdotes of 110 year old men who sit on their ass all day chain smoking unfiltered Camels and eating 5 pounds of bacon a day and washing it all down with Thunderbird wine. And you can not smoke, not drink, run 10 miles a day, and live by eating nothing but tofu, broccoli, and wicker and die of a heart attack at 45. Behavioral effects on health are measurable across large populations, and you should probably do whatever you can to improve your own health, but you can do nothing at all to guarantee that you will live longer only because you do everything you are "supposed" to do. --Jayron32.talk.contribs 21:27, 18 April 2009 (UTC)

I understand this. Sadly, my mother uses this as justification to continue smoking while immobile in a chair. Vimescarrot (talk) 22:04, 18 April 2009 (UTC)

Yes - but it's a matter of probability. One person in a thousand who does all of those terrible things to their body will survive - but the other 999 will die an early death. Sure, there are anecdotes of individuals who smoked their entire lives and through sheer, blind luck survived. On the other hand, you have people like my father who tragically died in his early 50's from smoking just 10 cigarettes a day - or like my mother who suffered from most of the bllod pressure and heart disease symptoms of a 10-a-day smoker despite never having smoked in her life because of the second-hand smoke. That my father died so young is probably the only thing that saved my mother from doing the same. Picking the one person in a thousand who survived and hoping that you'll also be that lucky one person in a thousand and not one of the 999 more typical cases is exactly like saying "I'm going to give up working and assume that I'll win the lottery" - nobody in their right mind does that yet it's the exact same ridiculous thinking pattern. SteveBaker (talk) 19:29, 19 April 2009 (UTC)

It kind of depends on your exit-strategy. Do you want to live with maximal indulgence and go out with a bang? Suffer through lingering health problems? Exercise will improve your cardiac state, help your lung capacity to a certain extent and improve your feeling of general wellbeing - but there's all that dicomfort and sweating. Improved diet will lessen your risk of atherosclerosis, stroke and metabolic syndrome/diabetes - but there's the factor of being hungry all the time. Quitting smoking improves almost every risk factor there is (not diabetes) - but that could just mean you spend a long life wishing every minute of the day that you could have another smoke.

If quitting the evil weed is off the table, then a little of both of the other two. A half-hour brisk walk every day is a good start and eatcher veggies. But really, anything other than continuing to sit in a chair smoking and eating pork rinds is probably going to be an improvement. In the end though, everyone chooses their own way out the door.

Maybe you need to engage with your mother more - offer to cook some neat recipes and ask her to go out on regular walks with you. That way you get an equal benefit. Franamax (talk) 22:24, 18 April 2009 (UTC)

Exercise should be enjoyable if done correctly (endorphins and all that), and a healthy diet shouldn't leave you feeling hungry unless you are trying to lose weight (which should only by a short term issue). --Tango (talk) 01:02, 19 April 2009 (UTC)

For a heavy smoker, the answer is very likely stopping smoking. The other things make a difference, but unless the person is an inert obese blob, not as huge a difference as smoking. Looie496 (talk) 02:22, 19 April 2009 (UTC)

A mixture of OR, unsourced and read from sources but not cited:

@Tango, granted on the endorphin reward, but they take time to develop hence the initial discomfort. There's also the social factor, which is overall important. I tried working out at a gym once and didn't return. OTOH I will go for multihour walks with my friends or family anywhere and always. And despite the obvious handicap of being a smoker, I love playing squash, just because I'm competing against myself as much as the other player. Plus it's among the most exertive of sports, so you get the good stuff that much faster I suppose. :)

And the unsourced part is to feeling hunger pangs. Perhaps I should call them cravings. Long-term exposure to high-sugar and/or high-fat diets set up feedback rhythyms which can result in habitual behaviour. Our reward systems are treated independently in our wiki articles - since I'm in the "unsourced/OR" bit here, I'll point out the large number of neurons comprising the "gut brain" concerned exclusively with feeding.

@Looie - oh yes, undoubtedly quitting smoking is much more than the "likely" answer. The way the OP posed it as a simple choice, it wins hands down. I'm pretty sure the various physiologists who attend this page will agree with me on the risk factors. Trouble is that life is a little more complicated than that. You have to address the risk factors that are easiest to change (IMO) first. To use your terminology, the OP was in a way describing an "inert obese blob" they are very concerned about. They wish to modify someone else's lifestyle and outlook. There's a lot of factors there beyond just presenting "what the people on Wikipedia said". But yes of course, quit smoking! Easier said than done. :( Franamax (talk) 03:24, 19 April 2009 (UTC)

These activities complement each other nicely. When a heavy-smoking friend of mine started exercising, he found his desire for cigarettes decreasing. Conversely, if one stops smoking, then one breathes better, and might feel more like getting up and exercising! -GTBacchus^(talk) 02:44, 19 April 2009 (UTC)

The classic studies are MRFIT (Multiple Risk Factor Intervention Trial) and the Framingham Heart Study, although I don't have access to those studies at the moment. This study included 84,129 women. Relative risks of coronary events:-

Relative risk of coronary events over 14 years in the Nurses' Health Study

Risk factor	Increase in relative risk
Poor diet (quintile 1) vs. good diet (quintile 5)	1.90
Smoking ≥ 15 cigarettes per day vs. ex-smoker	3.5
Exercise < 1 hour per week vs. > 5.5 hours per week	1.41

However this study was a cohort study, not an intervention trial. Axl ¤ [Talk] 18:08, 19 April 2009 (UTC)

Give up smoking - by a very large margin. Our article Smoking cessation gives a TON of useful information - what techniques for giving up work best, etc. I'll quote this for you because I think it's inspirational for the person doing the quitting:

The immediate effects of smoking cessation include:

• Within 20 minutes blood pressure returns to its normal level
• After 8 hours oxygen levels return to normal
• After 24 hours carbon monoxide levels in the lungs return to those of a non-smoker and the mucus begins to clear
• After 48 hours nicotine leaves the body and tastebuds are improved
• After 72 hours breathing becomes easier
• After 2–12 weeks, circulation improves
• After 5 years, the risk of heart attack falls to about half that of a smoker
• After 10 years, the chance of lung cancer is almost the same as a non-smoker.

If the person doing the quitting can understand on a day by day basis what's getting better - they'll be more inclined to stick with it.

I don't think you'll get such immediate or profound benefits from either diet or exercise. However, it's very hard to be specific without a lot more information - and in any case, we're not allowed to give that kind of specific medical advice. Probably the very best advice we can give is "Go see a doctor" - they can weigh the pro's and con's with full knowledge of the state of the person involved. SteveBaker (talk) 19:19, 19 April 2009 (UTC)

Having quit once for 8 years, I can testify that the effects are immediate and profound. Not all of them beneficial, like searching the ashtrays in the basement to find stale old butts and light them up for two more drags, right down to the cellulose acetate in the filter. Overall, yes of course it's good to quit smoking (although I didn't have one-half a heart attack in those years, so I can't confirm your statistic ;). But the little trap in my brain circuitry was still poised, it never went away - 8 years later when a friend offered me a $200 Cohiba at a wedding (I just had to destroy that value, c'mon), the trap was sprung.

My point is that all risk factors exist, but some can be mitigated more easily than others. It's not a trinary choice, it's a matter of what can most easily be achieved in the circumstances. GTB puts it well, an overall approach yields synergy. That's not what the OP asked originally, but they later revealed their overall concern - so I suggest an overall approach. It's what I do with my own mum, she's made her own decision to keep smoking - but she smokes nothing when we go hiking. :) PS: I understand that this is not a scientific response Franamax (talk) 19:50, 19 April 2009 (UTC)

Actually, my overall concern is not with my mother. I was genuinely just curious. If I try any sort of logical approach with my mother, depending on her mood, she'll either look at me like I'm a joke, look at me like I'm stupid, or look at me like she's never seen me before. Oh - and thank you, everyone, for your epic input. Uhm...I apologise if you were only doing it because you thought it would be in some way functional. :( Vimescarrot (talk) 23:11, 19 April 2009 (UTC)