大物振动课件解析.pptVIP

Answer: All three.A stable equilibrium point is needed. In addition, some sort of disturbance is required to set the object in motion (otherwise the object would simply remain at the equilibrium point). Finally, friction should be small or absent, otherwise the object doesn’t oscillate but just returns to the equilibrium point without overshooting it. Answer: 3.The velocity is zero at the maxima and minima of the curve.At these points, the curve is concave either up or down, and so the particle is accelerating.The particle has zero acceleration at the points of inflection of the curve, which occur at those times t for which x = 0. At these points, the curve has nonzero slope and so the velocity cannot be zero. Answer: 1. If released from its new position, the object accelerates upward and passes the equilibrium point with nonzero velocity. The object has therefore gained kinetic energy. The two forms of potential energy present are elastic potential energy of the spring and gravitational potential energy. Even though the latter decreases as the object is pulled down, the sum of the two must increase for the object to be able to gain kinetic energy. Answer: 2. Oscillations are an interplay between inertia and a restoring force. The extra person doubles both the rotational inertia of the swing as well as the restoring torque. The two effects cancel. Answer: 1. By standing up, the distance of the center of mass to the pivot point is reduced. The restoring torque decreases linearly with this distance; the rotational inertia as the square of it. Thus, the rotational inertia decreases more and the period decreases. Answer: 1.The frequency of the envelope of the beat function is proportional to the difference in frequency between the two waves.The greater the difference in frequency, the greater the frequency of the envelope. Answer: 2. The frequency of the oscillation within the beats is equal to the average of the original frequencies. Answer: 2. After 1/30th of a