Commons

m / This Air Force doctor volunteered to ride a rocket sled as amedical experiment. The obvious effects on his head and face are notbecause of the sled’s speed but because of its rapid changes in speed:increasing in 2 and 3, and decreasing in 5 and 6. In 4 his speed isgreatest, but because his speed is not increasing or decreasing verymuch at this moment, there is little effect on him.(figure n) whose oscillations would persist for many hours withoutbecoming imperceptible. Although Foucault did his demonstrationin Paris, it’s easier to imagine what would happen at thenorth pole: the pendulum would keep swinging in the same plane,but the earth would spin underneath it once every 24 hours. Tosomeone standing in the snow, it would appear that the pendulum’splane of motion was twisting. The effect at latitudes lessthan 90 degrees turns out to be slower, but otherwise similar. TheFoucault pendulum was the first definitive experimental proof thatthe earth really did spin on its axis, although scientists had beenconvinced of its rotation for a century based on more indirect evidenceabout the structure of the solar system.People have a strong intuitive belief that there is a state of absoluterest, and that the earth’s surface defines it. But Copernicusproposed as a mathematical assumption, and Galileo argued as amatter of physical reality, that the earth spins on its axis, and alsocircles the sun. Galileo’s opponents objected that this was impossible,because we would observe the effects of the motion. They said,for example, that if the earth was moving, then you would neverbe able to jump up in the air and land in the same place again —the earth would have moved out from under you. Galileo realized18 Chapter 1 Conservation of Mass and Energy