Bản chất của vật lý trong cuộc sống
[...]... metal The crucial point was that the total mass of the entire apparatus was exactly the same before and after the reaction Based on many observations of this type, Lavoisier proposed a general law of nature, that mass is always conserved (In earlier experiments, in which closed systems were not used, chemists had become convinced that there was a mysterious substance, phlogiston, involved in combustion... cycle However, the curve of the motion is so gentle that under ordinary conditions we don’t notice that the local dirt’s frame of reference isn’t quite inertial The first demonstration of the noninertial nature of the earth-fixed frame of reference was by Foucault using a very massive pendulum (figure c) whose oscillations would persist for many hours without becoming imperceptible Although Foucault did... decreasing very much at this moment, there is little effect on him (U.S Air Force) Observers in different inertial frames of reference will disagree on velocities, but agree on accelerations Let’s keep it simple by continuing to work in one dimension One frame of reference uses a coordinate system x1 , and the other we label x2 If the positive x1 and x2 axes point in the same direction, then in general... point of this discussion is not to get you to do numerical exercises with E = mc2 (at this point you don’t even know what units are used to measure energy), but simply to point out to you the empirical nature of the laws of physics If a previously accepted theory is contradicted by an experiment, then the theory needs to be changed This is also a good example of something called the correspondence principle,... synonym for ugliness If we have to keep on adding more and more forms of energy to our laundry list, then it’s starting to sound like energy is distressingly complicated Luckily it turns out that energy is simpler than it seems Many forms of energy that are apparently unrelated turn out to be manifestations of a small number of forms at the atomic level, and this is the topic of section 2.4 Discussion Questions