Lecture 3 Energy

# Lecture 3 Energy - Energy 1 Energy definition and units...

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Energy- 1 Energy: definition and units First Law of Thermodynamics: Law of conservation of energy. Second Law of Thermodynamics Energy and chemical reactions Energy and order in biological systems Solar energy

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Energy: definition and units Energy is a physical quantity that is a property of objects and systems. Energy is often defined as the ability to do work. Energy exists in two main forms : A) Potential energy: energy stored within a physical system. This energy can be released or converted into other forms of energy, including kinetic energy. It is called potential energy because it has the potential to change the states of objects in the system when the energy is released. Energy stored by position: water at the top of a waterfall. Energy stored in chemical bonds: fuel (coal, gasoline, natural gas); foods (carbohydrates, fats, proteins). Energy stored in bound nuclear particles: nuclear energy. B) Kinetic energy: The kinetic energy of an object is the extra energy which it possesses due to its motion. Examples: a nuclear explosion; a spinning waterwheel; a rolling freight train; electrical energy; radiant energy (movement of electromagnetic waves). Thermal energy: It is the energy associated with molecular motion, including translation, vibration, and rotation. Heat is the movement of thermal energy. Thermal energy travels from higher to lower energy. Matter does not contain heat. Matter contains thermal energy. Heat is thermal energy in transit. Energy flows until thermal equilibrium is reached.
Problem 1 How much electrical energy, in joules, is consumed by a 75-W bulb burning for 1.0 hr? Units: 1 calorie is the amount of heat required to raise the temperature of a gram of water from 14.5 °C to 15.5 °C at standard atmospheric pressure. In most fields, its use is archaic, and the SI unit of energy, the joule , has become accepted. 1 calorie is approximately 4.184 joules. Power (symbol: P ) is the amount of energy required or expended for a given unit of time; the SI unit of power is the watt (1 joule/s).

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The First Law states that energy cannot be created or destroyed; rather, the amount of energy lost in a process cannot be greater than the amount of energy gained. The total amount of energy in any isolated system remains constant but cannot be recreated, although it may change forms, e.g. friction turns kinetic energy into thermal energy. The total energy of the Universe is constant.
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Lecture 3 Energy - Energy 1 Energy definition and units...

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