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15.1 Energy and Its Forms Energy is the ability to do work. Work is actually a transfer of energy. When work is done to an object, energy is transferred to that object. Energy is measured in joules (J) – just like work. Energy can take several different forms. Mechanical Energy is the sum of potential and kinetic energy. Thermal Energy is the sum of potential and kinetic energy of all the particles in an object. Measured as temperature. Chemical Energy is stored energy in chemical bonds. Electrical Energy is the transfer of electric charges. Electromagnetic Energy is energy that travels through space as waves. Sunlight, radio-waves and X-rays Nuclear Energy is the stored energy that holds together the nucleus of an atom. Nuclear fission is a process that splits the nucleus apart to release nuclear energy. 2 types of Mechanical Energy: kinetic energy and potential energy Kinetic Energy (KE) is the energy of motion. All moving objects have KE. The kinetic energy depends on an object’s mass and speed. The mathematical equation for KE: KE = ½ mv2 More mass more KE Greater speed greater kinetic energy KE is more dependant on speed than mass (speed is squared) Potential Energy (PE) is energy that is stored in an object as a result of its position or shape. 2 types of potential energy: 1. Gravitational Potential Energy (PEg) An object gains gravitational potential energy when it is raised to a greater height. The mathematical equation for PEg: PEg = m ag h 2. Elastic Potential Energy (PEe). An object gains elastic potential energy when it is stretched or is pressed together. For example, stretching a rubber band or pressing a spring gives the object elastic potential energy. Calculating Kinetic Energy A 0.10-kilogram bird is flying at a constant speed of 8.0 m/s. What is the bird’s kinetic energy? Givens What information are you given? Mass, m = 0.10 kg Speed, v = 8.0 m/s What unknown are you trying to calculate? Kinetic energy of the bird, KE =? Plan and Solve What equation contains the given quantities and the unknown? KE = ½ mv2 Substitute the known values in the formula for KE. KE = ½ (0.10 kg)(8.0 m/s)2 = ½ (0.10 kg)(64 m2/s2) KE = 3.2 kg m2/s2 = 3.2 N m = 3.2 J Look Back and Check Is your answer reasonable? Yes, small bird (mass) = small KE