Can the elastic force in the spring be mutated? Liu Ruiyang (Juye County Experimental Middle School, Shandong Juye 274900) has such an example in a magazine: as shown in Figure 1, there are three identical balls A, B and C, respectively. The light rope, light rod and light spring are fixed and in a stationary state. What is the magnitude and direction of the acceleration of A, B and C at the moment of cutting the horizontal, light and light springs in the horizontal direction? Figure 1 is mentioned in the analysis: the key to analyzing this problem is light rope and light The change of the elastic force in the rod and the light spring. The elastic force in the ideal light rope and light rod can be abrupt, and the elastic force change does not require time, and the change of spring elasticity takes time and cannot be changed. The author thinks that this is not appropriate for the spring.
From Newton's second law F=ma, because of m0, a, the time used for the motion displacement x is t=2xa0. Therefore, the spring force in the spring can be abrupt, which is also found in the Shanghai college entrance examination questions. If you can't mutate, the moment the pin is removed, the acceleration of the ball should still be zero, but this contradicts the test. According to the statement that it can be mutated, the problem can be solved. For the spring on the right side of Figure 1, when the left horizontal spring is cut, one end is fixed at the other end and the other end has a small ball of mass. For the same reason Newton's second law is: a = Fm, t = 2xa, because m0, F0, x0, so t0, that is, the spring tension can not be abrupt in this case. In general, whether the elastic force of the light spring can be abruptly changed can be as follows: (1) When the spring end is free, the elastic force can be abrupt; (2) When there are objects at both ends of the spring, the elastic force cannot be abruptly changed.
Using this method to detect neutrinos is really a needle in the sea, and its arduousness can be imagined. The Davis experiment lasted for about 30 years, and a total of about 2000 e were detected. Observing the solar neutrino directly proves that the interior of the sun is indeed undergoing a nuclear fusion reaction from hydrogen polymerization to helium. However, compared with the theoretical value of the solar neutrino, the flow rate is less than half. This is the famous case of the missing sun neutrino. In the 1980s, Xiaochai Changjun and others used the deep-water Cherenkov technique in Japan. Another large neutrino detector buried in the mine. This is a large pool of dense photomultiplier tubes. When a neutrino collides in a large pool to produce a high-energy electron, the Cherenkov photons generated by the electrons in the water are detected by the photomultiplier tube. In the 1990s, Xiao Chai Changjun and others further developed this technology, and built a super-Kamioka detector with 50,000 tons of water and more than 10,000 photomultiplier tubes.
On February 23, 1987, a supernova (SN1987A) broke out in the Great Magellanic Cloud. This is the first time in 400 years that there are so close supernovas visible to the naked eye. Xiaochai Changjun's Kamogawa detector observed the neutrino from this supernova, which is the first time humans have observed cosmic neutrinos other than the sun. This type of detection is extremely difficult, and they actually detected 12 out of the 11016 neutrinos that hit the detector. This successful detection directly proves that a neutron star was formed during the supernova explosion. The original neutrino was produced when the proton was converted into a neutron during the supernova explosion. The discovery of Raymond Davis and Xiao Chai Changjun opened up a new field whose importance lies in the birth of neutrino astronomy and X-ray astronomy, opening two new windows for human observation of the universe. Their awards are well deserved.
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