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Tuesday, December 3, 2013


In the past few days, I have been reminded of the broad range of expert knowledge among the visitors to this blog.  Professor Goldfarb corrected my false notion that Memorial Hall at Harvard is a memorial to the fallen on both sides in the Civil War [he graciously suggested I might be confusing it with Memorial Church, but no such luck -- I was just wrong.]  Professor Ogilvie of the UMass History Department pointed out that the original creator of Benjamin Franklin "Hawkeye" Pierce attended Bowdoin and Cornell, not Harvard [although I still cling to the fragment of a notion that he might have visited Harvard and seen the inscription].  And several of you responded to my idle and ignorant remark about the lack of serious classical compositions for string trio by pointing me toward significant counter-instances, with none of which I was familiar.

I was turning this over in my mind during my morning walk, when it occurred to me that perhaps all of you collectively might be able to answer some questions that have nagged at me for years.  I could of course try Google, but that is so 2012.  The new thing is crowdsourcing, so let's see whether it works.  Here are three things that puzzle me.  Can anyone shed light on one or another of them?

1.  How does soap work?  I mean, I understand why rinsing your hands in water, rubbing as you rinse, might shake loose some bits of dirt and carry them away, but why does it help to use soap?  By way of contrast, my Dental Hygienist has counseled me that the proper way to clean my teeth is to start by flossing, which if done well loosens the plaque that has built up;  then to brush with a bare brush to complete the removal of the plaque, and then to apply the prescription fluoride toothpaste [after which one is not to eat or drink for twenty minutes, an injunction I honor more in the breach than the observance.]  She says using toothpaste just confuses things and does not do any additional good.  So, if that is true, what good is soap?

2.   How can stunt planes at aerial circuses fly upside down?  I learned all about Bernoulli's Principle and the differential pressure under and over the wing created by the curved upper surface of the wing, thus creating upward pressure that lifts the airplane, but if all of that is true, why doesn't an airplane crash when it flies upside down?

3.  How does friction work?  Friction is a ubiquitous phenomenon, as common as gravity.  But I have no idea how it works.  Why do some things produce friction when rubbed against one another whereas other things do not?  Why is ice virtually frictionless?  In the summer, when it is very warm here in North Carolina even early in the morning during my walk, I am liable to return home sweaty, whereupon friction gets in the way of my taking my T-shirt off, whereas in the Winter, it comes off easily.  How come?

I await your collective enlightenment.


NAL said...

1) Soap removes the oil that skin produces. Dirt adheres to this oil.

2) How Airplanes Fly:

A plane flies upside down. The physical view has no problem with this. The plane adjusts the angle of attack of the inverted wing to give the desired lift. The popular explanation implies that inverted flight is impossible.

3) I don't know. But, a sweaty t-shirt would contact the body in more places than a non-sweaty t-shirt. People sweat less in winter, the body doesn't need as much sweat to keep itself cool.

decessero said...

While i wish i could enlighten your august self on all these profound matters, i shall assay but one. To this end, here are the ten top reasons for using soap:

1. Soap surely represents a significant percentage of the total personal care industry and is thus essential to moneybag’s interests which we must foster.

2. Water alone doesn’t seem to do a great job on the less desirable olfactory signature.

3. Peroxide stings on open skin areas.

4. Salt is too abrasive as well as stinging on open skin areas.

5. Chlorine (bleach) kills germs but can cause tissue damage.

6. Olive oil has its advantages but might prove too slippery for certain activities.

7. Strigils are harsh and a bit archaic.

8. Chocolate discolors and leaves a residue.

9. Soap is particularly pleasant when showering with a friend.

10. Our mommies told us to.

David Auerbach said...

Ice isn't frictionless. But you don't skate (or slip) on ice. You skate (or slip) on (liquid) water. If the ice didn't melt (from the *friction*) then you couldn't skate (or slip)
If I remember correctly friction is very complicated; not descriptively (coefficient of starting friction, coefficient of friction, etc. ) but at the micro level. Something to do with actual interactions (bonds) between the materials. (and remember that when you're experiencing "friction" you might be, in part, falsely counting in the component of force perpendicular to the surface.
Soaps (and detergents) emulsify.

NAL said...

Should I brush or floss first?(ADA):

Either way is acceptable as long as you do a thorough job. However, if you use dental floss before you brush, the fluoride from the toothpaste has a better chance of reaching between teeth. Some people brush their teeth and unfortunately skip flossing because they think their mouth feels clean or they may be short on time or tired and flossing is postponed. That’s not a good idea.

Warren Goldfarb said...

On an earlier matter: Franklin Pierce (the American president) was a Bowdoin graduate. Benjamin Pierce, Benjamin Franklin Pierce was the name of his son, who died at the age of 12. Benjamin Pierce was the name of his father, a Revolutionary War hero and governor of N.H. I think a Bowdoin connection is far likelier than the author's seeing the plaque in Mem Hall. (I do not know whether the B.F. Pierce who is memorialized there had any connection to the president's family.)

Robert Paul Wolff said...

I must say, Warren, that is looking more and more plausible! Oh well, at least I can attest by personal experience for the Beaux Arts trio story.

Seth said...


Typical molecules used for soaps/detergents have a long, straight, oil-like part and a small bulb-like electrically 'polar' (electric charge is sort of lopsided) part. The oil-like part will get mixed into the grease/dirt and the polar/bulb part will mix in with water. This isolates the greasy 'dirt' within a water solution, which allows the water to rinse away carrying the dirt.

The site above has a nice little animation. There are probably better ones available, but they might involve installing Java and other related confusing, error-prone steps.

btw: this behavior of soap molecules is closely related to cell membranes, which are basically 'bilipid' layers. Two layers of 'soap bubble' one inside the other, with the bulb ends facing away from each other.

Robert Paul Wolff said...

cool. Thank you. That makes sense.

David Auerbach said...

There's a wonderful book that covers much of the science behind (some rather particular) everyday phenomena. It's a great browse and a great myth-dispeller.
Harold McGee:On Food and Cooking: The Science and Lore of the Kitchen

A (by now well-known) nugget: when you brown meat (as for for a stew or fricasee) you aren't "sealing in the juices". Cookbooks, even by chefs who should know better, routinely say this. But, once you think about it you realize it makes no sense at all. And yet, there is a good reasoning for browning--just not sealing.

In any case, great book.

Robert Paul Wolff said...

David, inasmuch as you are the potato latke maven, I take your recommendation of this book, with the utmost seriousness.

Unknown said...

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Kind Regards
Daniel Warn