Energy & Thermodynamics Internal Energy: All objects are made of particles in constant random motion. As these particles interact, their kinetic and potential energies may change, but the sum of kinetic energy and potential energy does not change. This total energy is called the internal energy of the object. An object’s Internal Energy depends on: • its material composition • its mass • its temperature • and its physical state (solid, gas, etc.) Increasing Internal Energy: Internal energy can be transferred from one object to another if they have different temperatures. This energy transfer is called HEAT. Another way to change an object’s internal energy is by doing some work on it. Example: Rubbing your hands together uses friction to raise their temperature. So an object’s internal energy can be increased by adding heat, or by doing work on the object. Decreasing Internal Energy: The reverse is also true – an object’s internal energy can be decreased by removing heat or by the object doing work. Thermodynamics: The science of dealing with the relationships between internal energy, heat, and work is called thermodynamics. First Law of Thermodynamics: The First Law of Thermodynamics states that when work is done on a system, some of the work is changed to heat (thermal) energy. Examples of First Law: Example: A car engine heats up as it runs due to friction between the moving parts Another Example: As a roller coaster moves down from the highest point on the track, some of its potential energy is changed into kinetic energy, sound energy, and thermal energy (due to friction). The original energy (potential energy) is equal to the sum of the kinetic energy, sound energy and thermal energy. Heat Engines: Heat Engines convert thermal energy to mechanical energy. All heat engines: • Absorb thermal energy from a high temperature source. • Convert some of the thermal energy to work. • Discard the remaining thermal energy into a low temperature “sink.” Examples of Heat Engines: Examples of Heat Engines: • Car engines which use the energy from hot gases to turn the wheels and work other equipment. Excess heat and exhaust are released to the atmosphere. • The Space Shuttle uses a chemical reaction between hydrogen and oxygen for energy. • Your body uses the food you eat for energy. -2Refrigerators and Heat Pumps: Refrigerators and Heat Pumps operate in a cycle that is the reverse of the heat engine. Refrigerators and Heat Pumps convert work to thermal energy and move heat away from a cold reservoir to a hot reservoir. • Refrigerators use a refrigerant (working fluid) to absorb heat from the cold inside and release that heat to the warmer outside. • Heat pumps work much the same way to cool in the summer, but can be reversed to heat in the winter. Second Law of Thermodynamics: The Second Law of Thermodynamics states that when work is done, some energy must be transferred to the surrounding system, and becomes unavailable for further use. i.e. No system can convert 100% of the available to energy to usable forms. Example of Second Law: Energy Dissipation: Examples of Energy Dissipation: Example: As a roller coaster moves down the hill, the gain in kinetic energy will always be less than the loss in potential energy since some of the energy is converted to sound and to thermal energy (friction that heats up the track). Energy is not “used up” in mechanical, fluid, electrical or thermal systems. But some energy is converted from usable forms to unusable forms. Example: When electrical energy flows through a light bulb, some of the energy produces visible light and some is dissipated as thermal energy that heats the bulb. Another Example: When gasoline is burned in a car engine, some of the energy produces motion and operates equipment, and some of the energy is dissipated as thermal energy that heats the earth’s atmosphere. Energy dissipation means there may never be a shortage of energy on the earth, but someday there may be a shortage of energy in usable forms.