Physics foibles

Posted on August 18, 2007 by Steve

When Richard Feynman was asked to review textbooks for the California Board of Education, he was continually incensed by the errors he found:

Finally I come to a book that says, "Mathematics is used in science in many ways. We will give you an example from astronomy, which is the science of stars." I turn the page, and it says, "Red stars have a temperature of four thousand degrees, yellow stars have a temperature of five thousand degrees . . ." -- so far, so good. It continues: "Green stars have a temperature of seven thousand degrees, blue stars have a temperature of ten thousand degrees, and violet stars have a temperature of . . . (some big number)." There are no green or violet stars, but the figures for the others are roughly correct. It's vaguely right -- but already, trouble! That's the way everything was: Everything was written by somebody who didn't know what the hell he was talking about, so it was a little bit wrong, always! And how we are going to teach well by using books written by people who don't quite understand what they're talking about, I cannot understand. I don't know why, but the books are lousy; UNIVERSALLY LOUSY!

Anyway, I'm happy with this book, because it's the first example of applying arithmetic to science. I'm a bit unhappy when I read about the stars' temperatures, but I'm not very unhappy because it's more or less right -- it's just an example of error. Then comes the list of problems. It says, "John and his father go out to look at the stars. John sees two blue stars and a red star. His father sees a green star, a violet star, and two yellow stars. What is the total temperature of the stars seen by John and his father?" -- and I would explode in horror.

Has physics education improved since then? Test yourself with the following statements. Which are true, and which are oft-repeated misconceptions?

  1. Beams of light coming from the sun are parallel.
  2. An aircraft wing creates lift because air has to travel farther over the top surface than the bottom.
  3. Sound travels better through solids.
  4. The mass of an object is not related to the rate at which it falls.
  5. Electricity is the result of electrons moving through a conductor.
  6. Ponds form a skin of ice on their surface because ice is less dense than fluid water.
  7. Ignoring air resistance, an object dropped into a tunnel through the center of the earth would oscillate from end to end indefinitely.
  8. A lemon and metal strips can be used to light a flashlight bulb.
  9. Infrared light is a form of heat.
  10. Re-entering spacecraft are heated by friction with the air.

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Posted by beowulf | August 23, 2007 | 20:27:09

# Beams of light coming from the sun are parallel.

emanating from a sphere (or nearly a sphere) the rays must necessarily be non-parallel - however, they can be assumed to be parallel when striking the surface of the earth

right as far as it goes. the faster air creates a low pressure area and this low pressure area above the wing is responsible for the lift.


true - unless it begins to fall faster than about 0.6c where the massy equivalent of time dilation becomes large enough not to be ignored

true (I'm probably wrong on this one)



yes, weakly

??? - as far as I can tell that statement is nonsense. infrared light and "heat" are both electromagnetic radiation.

true (maybe)? is there something else that could cause the friction?

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