Comments on: Guess about 2 people will snark about this title

Guess about 2 people will snark about this title

Gyan — Tue, 18 Oct 2005 10:49:02 -0800

- approximations and the fun behind them.

By: weapons-grade pandemonium

weapons-grade pandemonium — Tue, 18 Oct 2005 11:02:53 -0800

Good post, Gyan. I read an interesting article on the Fermi principle in The Sciences magazine. When the first atomic bomb went off in New Mexico, Fermi threw some torn pieces of paper into the air, and from the distance they flew he estimated the power of the explosion. After all the official math was done, he was not far off the mark. Approximation works because, as when rounding off a restaurant bill, the errors tend to fall both directions and cancel one another.

By: justkevin

justkevin — Tue, 18 Oct 2005 11:13:59 -0800

Interesting stuff. My sister and I had a "back of the envelope" question this weekend: If there's a penny in my car's change drawer, how many miles will I drive before its extra weight has consumed its value in gasoline? Is it more or less than the expected lifespan of the car?

By: raedyn

raedyn — Tue, 18 Oct 2005 11:20:13 -0800

Cool link, Gyan. Thanks. We all use these ideas regularly (some more adeptly than others). It's interesting to step back and look at the process in more detail.

By: Smedleyman

Smedleyman — Tue, 18 Oct 2005 11:24:58 -0800

Not a snark - but must you have your thumb out, one eye shut, pencil behind your ear and your tongue sticking out the corner of your mouth while viewing the site? Some interesting stuff

By: donfactor

donfactor — Tue, 18 Oct 2005 11:36:22 -0800

Yeah, terrific site if you know what I mean

By: mkultra

mkultra — Tue, 18 Oct 2005 11:39:42 -0800

I love this stuff. I took a "we're going to explain the universe and how old everything is" course for non-scientists in college and this was the first thing our prof taught us. It's incredibly useful when you think about how much multiplication we (well, me at least) go through in our daily lives. OK, justkevin, how does this sound- your car weighs a ton (2000 lbs). A penny weighs .01 lbs. Your car holds 15 gallons of gas, and averages 20 mph, so a full tank will push you, let's see... 205 X 10 is 200, add another half that, and your car goes 300 miles on a tank of gas. At $3/gallon, that's about $50 to fill your car. $50/300mi is... well, 100/300 is .3, half that is $.15 per mile. Call it $.20, since we rounded down just before. A penny will take you 1/20 of a mile (.05mi). The penny is 1:(2X10^5) the weight of the car. If it takes $.20 to push the entire car 1 mile, it takes 20/(2X10^5), or 1/(10^4), or $.0001 to push the penny a mile. Ah, crap. Now my logic is failing me. How do I reconcile this all? Rewrote this page 1998.Mar.28. C'mon, what were you expecting?

By: weapons-grade pandemonium

weapons-grade pandemonium — Tue, 18 Oct 2005 12:08:25 -0800

On the other hand, if you don't have that penny in the car, you are destined to get a pile of change from that anal cashier when the bill is $40.01 and you give her three twenties and she doesn't have any tens or fives, sorry.

By: Smedleyman

Smedleyman — Tue, 18 Oct 2005 12:23:26 -0800

"Yeah, terrific site if you know what I mean posted by donfactor at 11:36 AM PST on October 18 [!]" Anal cashier, if you know what I mean.

By: selfmedicating

selfmedicating — Tue, 18 Oct 2005 12:26:45 -0800

mkultra and justkevin - so after 100 miles, the penny has cost a penny's worth of gas. Damn. Those fast food wrappers on the floor are costing me a fortune.

By: raedyn

raedyn — Tue, 18 Oct 2005 12:40:33 -0800

mkultra - I think you made it more coplicated than neccesary, but your logic is generally good. If the car averages 20 mpg*, and a gallon costs $3, then it costs $3 to push the whole car 20 miles. $3.00/20= $0.15 per mile to push the whole car. (I'll round up to $0.20 since the math is easier, and I'm in Canada where gas is actually more than that). Same answer, much simpler way of arriving at it. The problem is with your assumption re: the weight of a penny. It's not .01 lbs, but 0.1 oz, which is about 0.001 lbs. So you were off by an order of magnitude. The penny is 1/(2*10^6). It takes $0.20 for the whole car to go a mile, so 20 cents times the weight of the penny = $0.0000001 to push the penny a mile. The question was: how many miles will I drive before its extra weight has consumed its value in gasoline? Is it more or less than the expected lifespan of the car? So we are solving for D in the (made up) equation D*cost to push the penny a mile = $0.01 $0.01/$0.0000001 = 100,000 miles which is less than the expected lifespan of the car *I asssume you meant mpg, since mph has nothing to do with it. On preview: I don't know where selfmedicating got his/her answer from, but it's just wrong. It doesn't make sense.

By: raedyn

raedyn — Tue, 18 Oct 2005 12:42:33 -0800

When I said "The penny is 1/(2*10^6)." I meant it is 1/(2*10^6) the weight of the car, of course. (Damn I previewed that several times and never caught that. Sorry.)

By: Phantomx

Phantomx — Tue, 18 Oct 2005 12:46:09 -0800

smedleyman ... awesome comment Those of us in our senior design class had an imitation of our professor that went exactly that way. He always was suggesting back of the envelope calculations as a starting point and when a number was calculated that way he would strike that pose. Our entire class found ourselves doing that outside of the classroom all the time.

By: Phantomx

Phantomx — Tue, 18 Oct 2005 12:55:05 -0800

selfmedicating got his wrong answer from the last line of mkultra's calculation. he had 20/(2X10^5) when it should have been .20 which made the answer .0001 instead of .000001 which makes the answer 10,000 miles. which would also solve the order of magnitude difference between the answers

By: Phantomx

Phantomx — Tue, 18 Oct 2005 12:56:55 -0800

eek, sorry, that last one was a post of half thoughts, I should really put more thought into it. I hope the point gets across though.

By: 445supermag

445supermag — Tue, 18 Oct 2005 13:04:21 -0800

On the penny, the problem is that weight affects gas mileage mostly when accelerating and climbing hills. When traveling at a steady speed weight only adds to rolling resistance (the tires squish out a little more, the axle bearings have a little more friction). Most of the energy is used to overcome wind resistance and parasitic drag on the drivetrain (pumping oil, turning the engine, spinning gears under oil in the trans...). For example, even though a motorcycle may weigh less than 1/4 of a car and have 1/2 - 1/10 the motor, it only gets 2-3 times the mileage (45-80 mpg depending on size, horsepower...). I would decrease your estimates by a factor of 5-10.

By: 445supermag

445supermag — Tue, 18 Oct 2005 13:12:41 -0800

As an after thought, if weight were proportional to mileage, then 3 250 lb. passengers would decrease the milage of the theoretical car by 1/4 (or is it 1/5?).

By: Skwirl

Skwirl — Tue, 18 Oct 2005 13:19:03 -0800

The only way this clock could be more depressing would be if it asked a few questions, calculated your life expectancy and then ticked away at it.

By: alumshubby

alumshubby — Tue, 18 Oct 2005 13:29:52 -0800

Awhile back, there was this thread about the Megapenny Project...

By: PurplePorpoise

PurplePorpoise — Tue, 18 Oct 2005 13:39:50 -0800

Skwirl - that's a fantastic idea. There's the Death Clock which is similar but only takes into account sex, outlook, BMI, and smoking/non-smoking. 590,000,000 odd seconds left for me... (Sat Aug 11th, 2024 - ... WHAT?! I'll be dead by 46?!) Yes, it *does* count down...

By: bz

bz — Tue, 18 Oct 2005 14:23:03 -0800

A great, useful post, indeed. In recent weeks I have seen the "I am sorry for the length of my letter, but I had not the time to write a short one." attributed to Mark Twain and am happy to now know that it belongs to Blaise Pascal.

By: signal

signal — Tue, 18 Oct 2005 18:19:27 -0800

Fabulous. I use this sort of stuff all the time, especially the use-your-body-to-measure-stuff ones, and getting quick dirty estimates of, for instance, how many people a theater holds, how many books a bookshelf has, etc.

By: Kwantsar

Kwantsar — Tue, 18 Oct 2005 19:04:34 -0800

Gyan is MeFi's best poster.

By: Gyan

Gyan — Tue, 18 Oct 2005 20:06:07 -0800

I forgot, you take Paypal, right?

By: Kwantsar

Kwantsar — Thu, 20 Oct 2005 18:17:16 -0800

Now why would you go and cheapen my display of affection like that?

By: Gyan

Gyan — Thu, 20 Oct 2005 20:35:16 -0800

Your asking price was too high. /sheesh..just a joke