This energy is somewhat similar to chemical energy, since it is the energy associated with breaking or making molecular bonds, rather than atomic bonds. Latent heat - the energy needed to melt solids or boil liquids. Where dQ = the change in heat, c is the specific heat capacity in cal/gm K°, and dT = the change in temperature (in either C° or K°).Ĭhemical energy - the energy associated with breaking or making atomic bonds, i.e., with chemical transformations. Where m = the mass of the gas molecule (we assume the gas contains only one kind of molecule), v = the average velocity of the molecules, k B = Boltzmann's constant = 1.38 X 10 -23įor a solid or liquid of mass m, the change in heat energy can be related to the change in temperature by: In the case of a gas, where the molecules are moving freely, the average kinetic energy per molecule can be related to the absolute temperature by: This is more-or-less a special case of kinetic energy and elastic energy, because what we call thermal energy consists of the energy of many atoms. Where K = the spring constant (units of N / m), x 0 = the equilibrium position of the spring, and x = the distance the spring has been stretched or compressed. For a simple spring, the formula for elastic energy is: Rubber bands, springs, anything with tension on it, etc. The formula for kinetic energy is:Į = ½ mv 2 elastic energy - the energy contained in stretched or strained materials. Kinetic energy - the energy of moving bodies. Kilowatt-hour = (1000 J/s)(1 hr) X (60 min/hr)(60 sec/min) = 3,600,000 JĮnergy is a mysterious concept, not least because it comes in many guises. The conversion of a kilowatt-hour into joules is just: Since power = energy / time, it is also true that energy = power X time.) A kw-hr is a convenient quantity in the electric industry, because it is the energy equivalent of running a one-kilowatt appliance for one hour. Despite having the power-term "watt" in its name, the kw-hr is a unit of energy. Rather than using joules, the "kilowatt-hour" is commonly used by the electrical industry as a unit of energy. So, for example, a Hostess Twinkie with 200 calories contains 200 X 4168 = 833,600 joules, or enough energy to raise a 100-kilogram weight over half a mile! (Now you know why Twinkies are not normally considered to be diet food.) (There was a time when folks didn't realize that heat energy and mechanical energy are really one and the same, so they created separate definitions for them.) Thermodynamic measurements tell us that one calorie = 4.186 joule.īy the way - the "calorie" commonly used in measuring food energy is actually the kilocalorie, or Kcal for short. For example, if you lift a one-kilogram weight one meter, then the energy you must expend is:Į = Fd = (ma)d = mgd = (1 kg)(9.8m/s 2)(1 m) = 9.8 kg m/s 2 = 9.8 joules.Īn alternative definition of energy, the calorie, is defined as the amount of heat energy needed to raise the temperature of 1 gm of water 1 C°. A joule is the amount of energy needed to exert a force of one newton through one meter. Or put into words, energy is force acting through a distance, and power is the energy expended per second. Remembering that acceleration is defined as the rate of change of the velocity, or a = v / t, gives us the following table: Force, energy, and power are all related to each other in very specific ways. The first thing we must do is define our terms. Phyx 103-0, Energy Conservation of Energy
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