Simple Nature - Light and Matter

a new form of invisible “mystery energy” that patches things up?This would be like balancing your checkbook by putting in a faketransaction that makes your calculation of the balance agree withyour bank’s. If we could fudge this way, then conservation of energywould be untestable — impossible to prove or disprove.Actually all scientific theories are unprovable. A theory cannever be proved, because the experiments can only cover a finitenumber out of the infinitely many situations in which the theory issupposed to apply. Even a million experiments won’t suffice to proveit in the same sense of the word “proof” that is used in mathematics.However, even one experiment that contradicts a theory is sufficientto show that the theory is wrong. A theory that is immune todisproof is a bad theory, because there is no way to test it. Forinstance, if I say that 23 is the maximum number of angels thatcan dance on the head of a pin, I haven’t made a properly falsifiablescientific theory, since there’s no method by which anyone could evenattempt to prove me wrong based on observations or experiments.Conservation of energy is testable because new forms of energyare expected to show regular mathematical behavior, and are supposedto be related in a measurable way to observable phenomena.As an example, let’s see how to extend the energy concept to includemotion.c / As in figure b, an infraredcamera distinguishes hot andcold areas. As the bike skids toa stop with its brakes locked, thekinetic energy of the bike andrider is converted into heat inboth the floor (top) and the tire(bottom).2.1.3 Kinetic energyEnergy of motion is called kinetic energy. (The root of the wordis the same as the word “cinema” – in French, kinetic energy is“énergie cinétique.”) How does an object’s kinetic energy dependon its mass and velocity? Joule attempted a conceptually simpleexperiment on his honeymoon in the French-Swiss Alps near Mt.Chamonix, in which he measured the difference in temperature betweenthe top and bottom of a waterfall. The water at the top ofthe falls has some gravitational energy, which isn’t our subject rightnow, but as it drops, that gravitational energy is converted into kineticenergy, and then into heat energy due to internal friction inthe churning pool at the bottom:gravitational energy → kinetic energy → heat energyIn the logical framework of this book’s presentation of energy, thesignificance of the experiment is that it provides a way to find outhow an object’s kinetic energy depends on its mass and velocity. Theincrease in heat energy should equal the kinetic energy of the waterjust before impact, so in principle we could measure the water’smass, velocity, and kinetic energy, and see how they relate to oneanother. 33 From Joule’s point of view, the point of the experiment was different. Atthat time, most physicists believed that heat was a quantity that was conserved76 Chapter 2 Conservation of Energy