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Energy notes ENERGY IS THE ABILITY OF A PHYSICAL SYSTEM TO DO WORK 1. LAWS OF CONSERVATION OF MATTER/MASS…….. and ENERGY!!!!!!! The law of conservation of mass states that the mass of an isolated system (closed to all matter and energy) will remain constant over time The law of conservation of energy states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time. THE FIRST LAW OF THERMODYNAMICS STATES THAT IN A CLOSED SYSTEM, THE TOTAL AMOUNT OF ENERGY MUST REMAIN THE SAME. THAT MEANS THAT ENERGY CAN NEITHER BE CREATED NOR DESTROYED: IT CAN HOWEVER BE TRANSFORMED FROM ONE FORM TO ANOTHER. The energy into a system = the energy that comes out of the system THE SECOND LAW OF THERMODYNAMICS (COMES IN THREE FORMS) FORM 1: IN ANY TRANSFORMATION OF ENERGY FROM ONE FORM TO ANOTHER, THERE IS ALWAYS A DECREASE IN THE AMOUNT OF USEFUL ENERGY FORM 2: HEAT CANNOT, BY ITSELF, FLOW FROM COLD TO HOT. IT SPONTANEOUSLY FLOWS FROM HOT TO COLD. FORM 3: IN ANY CLOSED SYSTEM, DISORDER HAS A NATURAL TENDENCY TO INCREASE. Entropy increases if no energy is allowed to enter a system Entropy = disorder WHAT IS A SYSTEM? A system is an arrangement of parts which interact with each other within the system's boundaries to function as a whole. The nature (purpose) of the whole is always different from, and more than, the sum of its unassembled collection of parts. A system is a group of parts that does a specific job. CLOSED AND OPEN SYSTEMS: CLOSED SYSTEM—A SYSTEM WHERE NOTHING ENTERS OR LEAVES; WHERE EVERYTHING IS USED AND REUSED e.g. (Earth is a closed system with regard to matter) OPEN SYSTEM—A SYSTEM WHERE THINGS BOTH ENTER AND LEAVE e.g. (Earth is an open system with regard to energy) STEADY STATE— A SYSTEM IN WHICH PROPERTIES ARE CONSTANT BECAUSE SUBSTANCES ARE ENTERING AND LEAVING AT THE SAME RATE STATIC—showing little or no change: DYNAMIC—changing: THE SIX FORMS OF ENERGY: 1. MECHANICAL ENERGY—ENERGY OF MOTION OR POTENTIAL FOR MOTION 2. HEAT (THERMAL) ENERGY—FORM OF KINETIC ENERGY THAT FLOWS FROM ONE BODY TO ANOTHER BECAUSE OF A TEMPERATURE DIFFERENCE BETWEEN THEM. The effects of heat energy result from the motion of molecules. Heat energy is the kinetic energy of moving molecules Can be transferred in three ways: 1. conduction: is the transfer of energy through solid matter from particle to particle. Heat is conducted through a solid material much the same way electricity is. Conduction is slowed by insulation 2. convection: Convection is the transfer of heat energy through a gas or liquid by movement of currents. Heat is carried by the fluid 3. radiation: is electromagnetic waves which directly transport heat energy through space. Sunlight is radiated through space to our planet without the aid of fluids or solids 3. RADIANT ENERGY (INCLUDING LIGHT) This energy is demonstrated by the electromagnetic spectrum 4. ELECTRICAL ENERGY—the energy of electric charges. Never used as an end product in itself. It is used to make things do work, because it is easily converted into other forms of energy. 5. CHEMICAL ENERGY—energy stored in the bonds that hold molecules together. Common examples of chemical energy include: Foods Dried plant material (firewood!!!) Fossil fuels (gasoline, diesel, crude oil, coal) This energy is initially trapped by plants during photosynthesis! 6. NUCLEAR ENERGY—energy locked in the nuclei of atoms. When the particles that make up atomic nuclei are rearranged, energy is released WORK CAN ONLY BE DONE WHEN THERE IS A DIFFERENCE IN THE ENERGY CONTENT OF OBJECTS. TYPES OF ENERGY TRANSFER CONDUCTION-the transfer of thermal energy from molecule to molecule HEAT ENERGY FROM SOLID TO SOLID CONVECTION-the transfer of heat by the mass movement of heated particles as in air or liquid currents HEAT ENERGY THROUGH AIR RADIATION-that energy which is sent out from an object, like the sun or a light bulb-can be particles or waves In any energy conversion (from one form of energy to another,) some useful energy is lost to the environment as heat energy. This decreases the efficiency of the transformation. Energy EfficiencyThe efficiency of a machine equals the amount of energy that comes out of a machine divided by the energy that goes into a machine ALL multiplied by 100% (the multiplication factor exists because efficiency is expressed as a percent.) IE: efficiency = (useful energy out/ useful energy in) x 100% The efficiency of a system requires analyzing the efficiency of each step. If a system has three steps, and each step is 75% efficient, then the whole system’s efficiency can be expressed thus: (75%) x (75%) x (75%) = (.75) x (.75) x (.75) = 0.422 = 42%