Newtonian Mechanics

What’s weighs a newton?

posted Sunday, 25 April 2010

The newton is a unit of force. Weight is a force that we are all familiar with. Which of the following fruits has a weight that is closest to one newton?

macintosh apple red delicious apple cavensish banana
McIntosh Apple (151.3 g) Red Delicious Apple (216.4 g) Cavendish Banana (160.0 g)
valencia orange tangerine tomato
Valencia Orange (178.0 g) Tangerine (96.7 g) Tomato (152.8 g)
chicken egg    
Chicken Egg (65.9 g)    

Use the weight formula.

W = m g

Solve for mass. Substitute one newton for weight and one standard earth gravity for gravity.

m =  W  =  1 N  = 0.102 kg = 102 g
g 9.8 m/s2

The 96.7 gram tangerine comes closest to this value. Not all tangerines weigh 98.7 grams, however, so this is only a rule of thumb. There are certainly apples, bananas, oranges, tomatoes, and other fruits out there with a mass of approximately 102 grams and a weight of approximately one newton.

Those of you familiar with multiple choice tests should have eliminated the chicken egg as a possible answer. A chicken egg is only metaphorically the "fruit of the chicken".

A related problem for Americans only. Verify the rule of thumb that one newton is approximately equal to a quarter pound.

Here’s the way I usually do it — using values I’ve memorized from years of use.

 W =  mg 
 2.2 lb =  (1 kg)(9.8 m/s2) 
  1 lb =  4.45… N 
 1 N =  0.224… lb 

Here’s a more accurate way to do it — using values that are exact by definition.

 W =  mg 
 1 lb =  (0.45359237 kg)(9.80665 m/s2) 
 1 lb =  4.44822162… N 
 1 N =  0.224808943… lb 

Not quite a quarter pound, but you get the idea.

0.20 lb  <  0.224808943… lb  <  0.25 lb
 ⅕ lb   <  1 N  <  ¼ lb

The fraction 9/40 gives a decimal expansion of 0.225, which is accurate to three significant figures. Not my favorite fraction, but it gets the job done. With sixteen avoirdupois ounces in a pound, one newton is also about 3½ ounces.

1 N ≈  9 lb  ×  16 oz  =  18 oz  = 3½ oz
40 1 lb 5

Science caught in the Web 2010-04-17

posted Saturday, 17 April 2010

  • space stations (centrifugal force)

Science caught in the Web 2010-04-03

posted Saturday, 3 April 2010

Frisbee patent family tree

posted Sunday, 14 February 2010

US Patent D137521 US Patent 1404132 US Patent 2690339
Walter Frederick Morrison, inventor of the Frisbee, died Tuesday, 9 February 2010 at the age of 90. US design patent 183,626 for a "flying toy" was issued to Morrison on 30 September 1958. The Wham-O toy company (which also sold the hugely popular hula hoop) bought the rights to the Frisbee from Morrison in 1957 in return for lifetime royalties. US Patent D183626 Patent writers are required to cite "prior art". Morrison cited three US and one French patent in his application. He was in turn cited by at least 16 later patents — including a redesign of the Frisbee by Wham-O employee Ed Headrick, who claims to have been the toy’s true inventor. Headrick’s patent has been cited at least 81 times.
US Patent 4212131 US Patent 5290184 US Patent US Patent D266528
US Patent D295429 US Patent D310692 US Patent <empty>D346413 US Patent D346626
US Patent D347452 US Patent D349930 US Patent D390282 US Patent D405847
US Patent D464380 US Patent D552690 US Patent 5721315 US Patent 3359678
3930650 3948523 3959916 4031655 4080753 4086723 4132029 4151674 4151997 4153252 4152863 D251927 4157632 4174834 4196540 4204357 4205484 4216611 4253269 4265454 4288942 4431196 4456265 D275976 4516947 D286657 4669995 4681553 4737128 D295429 4802875 4889347 D310691 5009623 D337623 5232226 5254077 D341390 5263819 5269716 5290184 D346413 5326110 D349930 D350783 D356717 5423705 5484159 D369191 5531624 5540610 5553570 D386221 D386222 D386223 D387817 D388134 D390282 5799616 D398939 5816880 5829714 D401288 D401289 D402318 5964636 6073588 6179737 D445461 6585551 6755711 6764371 6918809 6971940 6991508 7081032 7217169 7270332 D562918 D564877 D568091

Science caught in the Web 2010-02-06

posted Saturday, 6 February 2010

Science caught in the Web 2010-01-30

posted Saturday, 30 January 2010

Science caught in the Web 2010-01-23

posted Saturday, 23 January 2010

Compressed Air Magazine

posted Friday, 1 January 2010

Compressed Air Magazine (CAM) was established in 1896 "to promote the capabilities of compressed air" — a new technology at the time. Compressed air is still important at the dawn of the Twenty-first Century, but the first few decades of this periodical are more fun to read than the current editions. (Check out the selections at the end of this post.) All 114 years are available for free — if you register — through the CAM website. Google Books has managed to scan a few volumes as of 2010. The Google scans look nicer, but the CAM website is absolutely complete and up to date.

I came across this particular article in after watching a documentary on Russia Today about the Moscow subway system. Twenty minutes into the video, a subway motorman comments on unusual barometer readings in certain tunnels. As he says this, he waves his hands in front of his instrument panel.

Is this a common event? Is barometric pressure routinely measured by subway motormen? I still don’t know, but a quick search turned up this article in CAM.

The author measured the barometric pressure in the first and last cars of a 1914 New York City subway train. At the time, the subway system was less than a decade old an consisted of only a single line — one that started in Brooklyn, ran up the east side of Manhattan, went crosstown on 42nd Street, continued uptown on Broadway, and ended in the Bronx. (This route is now a part of three different subway lines.) He was able to measure pressure variations caused by elevation changes and by position within the train. The latter of these effects would have been much more subtle in 1914 when subway trains were only three cars long. (Trains are now eight cars long on these lines.) I see a potential problem for The Physics Hypertextbook in here somewhere.

Flipping through the pages of this book brought me to this next data gem about a pneumatic grain elevator.

Mass flow rate appears to be directly proportional to the horsepower of the motor. Once again, how do I make this into a problem for The Physics Hypertextbook? Please enjoy the following selections from Compressed Air Magazine as you prepare your answer to these questions.

gas mask patent

The World’s Smallest Snowman

posted Thursday, 31 December 2009

The Hand of Google

posted Monday, 28 December 2009

I was trolling the Internet the other day looking for historical quotes about energy. I came across this mysterious image on the third page of a book at Google Books.


Behold, the hand of Google. Note that the hand of Google only needs to protect its fingertips. Competitors take note. The palm of the hand of Google is unprotected.

I also found the quote I was looking for. It’s one of the first written examples of the word energy being used in its modern sense.

The term energy may be applied, with great propriety, to the product of the mass or weight of a body, into the square of the number expressing its velocity.

This quote is from Thomas Young — of Young’s modulus and Young’s double slit experiment. I found it in Volume I of his 1807 magnum opus A Course of Lectures on Natural Philosophy and the Mechanical Arts. The image with the pink tipped hand came from Google’s copy of Volume II. They do not have a fully searchable copy of Volume I available yet. I had to go to U Penn’s Online Books Page to find both volumes. Volume I has all the text, so if you’re looking for a good Young quote start here. Volume II is mostly diagrams, so if you’re looking for old-timey scientific images for your website or ID3 art start there.