Simple Nature - Light and Matter

special “rest frame.” Since the air is moving along with the rotationof the earth, we don’t detect any special phenomena. To get asonic boom, the source of the sound would have to be movingrelative to the air.The Foucault pendulum example 4Note that in the example of the bowling ball in the truck, I didn’tclaim the sidewalk was exactly a Galilean frame of reference.This is because the sidewalk is moving in a circle due to the rotationof the Earth, and is therefore changing the direction of its motioncontinuously on a 24-hour cycle. However, the curve of themotion is so gentle that under ordinary conditions we don’t noticethat the local dirt’s frame of reference isn’t quite inertial. The firstdemonstration of the noninertial nature of the earth-fixed frame ofreference was by Foucault using a very massive pendulum (figured) whose oscillations would persist for many hours without becomingimperceptible. Although Foucault did his demonstration inParis, it’s easier to imagine what would happen at the north pole:the pendulum would keep swinging in the same plane, but theearth would spin underneath it once every 24 hours. To someonestanding in the snow, it would appear that the pendulum’s planeof motion was twisting. The effect at latitudes less than 90 degreesturns out to be slower, but otherwise similar. The Foucaultpendulum was the first definitive experimental proof that the earthreally did spin on its axis, although scientists had been convincedof its rotation for a century based on more indirect evidence aboutthe structure of the solar system.Although popular belief has Galileo being prosecuted by theCatholic Church for saying the earth rotated on its axis and also orbitedthe sun, Foucault’s pendulum was still centuries in the future,so Galileo had no hard proof; Galileo’s insights into relative versusabsolute motion simply made it more plausible that the world couldbe spinning without producing dramatic effects, but didn’t disprovethe contrary hypothesis that the sun, moon, and stars went aroundthe earth every 24 hours. Furthermore, the Church was much moreliberal and enlightened than most people believe. It didn’t (and stilldoesn’t) require a literal interpretation of the Bible, and one of theChurch officials involved in the Galileo affair wrote that “the Bibletells us how to go to heaven, not how the heavens go.” In otherwords, religion and science should be separate. The actual reasonGalileo got in trouble is shrouded in mystery, since Italy in the age ofthe Medicis was a secretive place where unscrupulous people mightsettle a score with poison or a false accusation of heresy. What is certainis that Galileo’s satirical style of scientific writing made manyenemies among the powerful Jesuit scholars who were his intellectualopponents — he compared one to a snake that doesn’t knowits own back is broken. It’s also possible that the Church was farless upset by his astronomical work than by his support for atomismd / Foucault demonstrateshis pendulum to an audience at alecture in 1851.e / Galileo’s trial.Section 1.3 Galilean Relativity 65