Radiophysics. Халюшева Г.Р. - 14 стр.

motion of the weight closely, you’ll observe that as the length of the string decreases, the speed of the weight increases and
vice versa. The longer the string, the slower the speed of the weight. Now, who can tell me, which of Newton’s laws
explains this phenomenon?
          A student: Force equals mass times acceleration.
          Teacher: That’s right. When a body in rotational motion moves in a radial direction, a force acts to speed up the
body, it the radial motion is toward the centre of rotation. Now think, when does the same force slow down the body?
          A student: The force slows down the body, it the radial motion is away from the centre.
          Teacher: Good. Does anyone know what we call this force?
          A student: If I’m not mistaken, it’s the Coriolis force.
          Teacher: No, you are not mistaken. So, this weight on the string experiment illustrates the speeding up and slowing
down effects on the string. In the case of an artificial satellite the string is replaced by the force of gravity. Who can tell me
what happens when the orbit of a satellite comes closer to the Earth’s?
          A student: I can. The radius of curvature of its path decreases, so the satellite must speed up.
          Teacher: Just so! Now, do you happen to know what law explains this effect when observed in cellestial bodies?
          A student: This effect is explained by Kepler’s law.
          Teacher: And what does this law state?
          A student: Let me see, it seems to me that Kepler stated that planets move in elliptical paths, with the Sun at one
focus of the ellipse, and that the line from a planet to the Sun sweeps over equal areas in equal times during all parts of its
path.
          Teacher: Oh, you seem to know the subject perfectly well. But there was also Newton’s third law – the law of
planetary motion. From this, Newton derived the inversesquare law for circular orbits. By the way, this law was derived by
at last three scientists besides Newton: by Robert Hooke, Edmund Halley and Christopher Wren. Do you know anything
about these scientists?
          A students: Well, Robert Hooke stated the principle of the spring balance.
          Teacher: And what about Halley?
          A students: I’ve read of Halley’s comet. Maybe it was he who predicted its approach?
          Teacher: Yes, the prediction was made at the end of the 17th century. Afterwards the comet was seen at regular
intervals of 75 years. Yet, Hally was unable to solve the problem of elliptical orbits himself. So he came to Newton and was
surprised to learn that the latter had solved it two years before. But as Newton had lost his calculations, he was forced to
perform the detailed mathematics all over again. You can well imagine the impression Newton’s work produced. It was in
1863. Then, Hally insisted that Newton should prepare his work for publication. As a result, in 1687 appeared the greatest
scientific book Mathematical Principles of Natural Philosophy, which contained the laws of motion, the law of gravitation
and much of Newton’s mathematical achievements. Now, what do you know about Wren?
          A student: Well, I’m not sure, but it seems that this name is connected with architecture. Or was it another Wren?
          Teacher: You are right. Wren was an outstanding English architect, the one that built St.Paul’s Cathedral in
London. There is the bell. After the interval I’ll give you some problems to solve.

         2.4.9 Notes to the Text

        A force acts to speed up the body – действует сила, которая ускоряет движение тела
        inverse–square law for circular orbits – закон обратный пропорциональности силы притяжения квадрату
расстояния для круговых орбит
        was surprised to learn – к своему удивлению узнал