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5.3 Types of Energy You use mechanical energy, a combination of gravitational potential and kinetic energy, to do mechanical work every day. There are many types of energy in the universe, all of which involve kinetic energy, potential energy, or both. Table 1 p.236 – Types of Energy Radiant Energy → also known as light energy, is energy possessed by oscillating electric and magnetic fields. Electrical Energy → energy possessed by accumulated static charges; static electricity. Energy possessed by flowing charges; current electricity. Thermal Energy → kinetic energy possessed by randomly moving atoms and molecules.

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5.3 Types of Energy Sound Energy → energy possessed by large groups of oscillating atoms and molecules. Nuclear Energy → also known as atomic energy, is energy possessed by protons and neutrons in atomic nuclei. Elastic Energy → energy possessed by materials that are stretched, compressed, or twisted and tend to return to their original form. Chemical Energy → also known as bond, fuel, food, or molecular energy, is energy associated with bonds in molecules.

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5.3 Energy Transformations The conversion of energy from one type to another is an energy transformation. Some examples include: Animals and humans transforming chemical energy from food into mechanical energy, which do work on objects in the environment. Plants transforming radiant energy, through photosynthesis, into chemical energy. Internal combustion engines transforming chemical energy from fuel into the mechanical energy of moving vehicles. Stoves transforming electrical energy into thermal and radiant energy.

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5.3 Law of Conservation of Energy Scientists have studied energy and energy transformations and have arrived at some important generalizations. They noticed that when one form of energy is transformed into another form (or forms) of energy, the quantity of the form reduced is the same amount as the quantity of the other forms increased. For example, a light bulb may transform 100 J of electrical energy into 5 J of radiant energy and 95 J of thermal energy. The Law of Conservation of Energy states: Energy is neither created nor destroyed; when energy is transformed from one form to another, no energy is lost.

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5.3 Quantifying Energy Transformations Total Mechanical Energy (E T ) is the sum of an object’s kinetic and gravitational potential energy at a particular moment. E T = E g + E K When solving problems using the law of conservation of energy, find the total mechanical energy at one moment (E T1 ) and equate it to the total mechanical energy at another moment (E T2 ). E T1 = E T2

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5.3 Quantifying Energy Transformations To illustrate the Law of Conservation of Energy, let us analyze the total mechanical energy of a diver, of mass 65 kg, at three different moments of a dive he is performing from a 10 m high platform: Moment 1: Before the Dive E T1 = E g1 + E k1 The diver is at rest on the platform of the diving tower. Since he is motionless, E k1 = 0 kJ. All of his energy is in the form of gravitational potential energy; E g1 = 6.4 kJ. E T1 = 6.4 kJ

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5.3 Quantifying Energy Transformations Moment 2: Midway Point of Dive E T2 = E g2 + E k2 The diver is midway between the platform and the surface of the water. Using a uniform acceleration equation, the diver’s speed is v = 9.9 m/s; his resulting kinetic energy is E k2 = 3.2 kJ. The remainder of his energy is in the form of gravitational potential energy from 5 m above the water; E g2 = 3.2 kJ. E T2 = 6.4 kJ

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5.3 Quantifying Energy Transformations Moment 3: At the Water’s Surface E T3 = E g3 + E k3 The diver reaches the surface of the water. Using a uniform acceleration equation, the diver’s speed at this point is v = 14 m/s; his resulting kinetic energy is E k3 = 6.4 kJ. Since the diver reaches the reference point, the gravitational potential energy is E g3 = 0 kJ. E T3 = 6.4 kJ Throughout the dive, the total mechanical energy did not change. SP # 1 p.240

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5.3 Homework Practice # 1 p.241 Questions # 1-4 p.241

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Energy: Forms and Changes

Energy: Forms and Changes

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