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Energy What is Energy? Energy The ability to do work. Work = force x distance Energy is measured in units called JOULES which can be abbreviated to J. Two Types of Energy: Kinetic and Potential Kinetic Energy: The energy of an object that is due to the objects motion. Kinetic energy = mv2/2 m = mass v2 = velocity squared Kinetic Energy Problems What is the kinetic energy of a car that has a mass of 2,400 kg and is moving at 20 m/s? REMEMBER: mv2/2 m = 2,400 and v = 20 m/s SO…. 2, 400 x 20 x 20/2 You have to multiply by 20 twice due to velocity being squared!!! Answer: 4,800,000 Joules (J) Problem #2 What is the kinetic energy of a 4,000 kg elephant that is running at 2 m/s? 4,000 x 2 x 2/2 Answer: 8,000 J Problem #3 What is the kinetic energy of a 2,000 kg bus that is moving at 30 m/s? 2,000 x 30 x 30/2 Answer: 900,000 J Final Kinetic Energy Problem What is the kinetic energy of a 3,000 bus that is moving at 20 m/s? 3,000 x 20 x 20/2 Answer: 600,000 J Potential Energy and Gravitational Potential Energy Potential Energy: energy that an object has because of the position, shape, or condition of the object…STORED energy. If the object has height the potential energy is known as GRAVITATIONAL POTENTIAL ENERGY. Gravitational Potential Energy GPE = weight x height What is the gravitational potential energy of a cat that weighs 40N standing on a table that is 0.8 m above the ground? 40 N x 0.8 m = 32 J GPE Problem #2 What is the gravitational potential energy of a diver who weighs 500N standing on a platform that is 10 m off the ground? 500 N x 10 m 5000 J GPE Problem #3 What is the gravitational potential energy of a diver who weighs 600 N standing on a platform that is 8 m off the ground? 600 N x 8 m 4800 J Mechanical Energy Mechanical Energy: the total energy of motion and position of an object mechanical energy = potential energy = kinetic energy Remember that mechanical energy stays the same unless some of it is transferred to another object. Five Forms of Energy Thermal Chemical Electromagnetic (electrical and light) Sound Nuclear Thermal (Heat) Energy Produced by random motion of particles that make up the object Examples: fire, friction, light bulb that has been on, sun, stove coils Chemical Energy Chemical Energy: energy of a compound that changes as its atoms are rearranged….a substance changes into a brand new substance. Examples: digested food, burning paper, rusting nail Electromagnetic Energy Electromagnetic energy: electrical and light energy combined….energy of moving charged particles. Examples: microwave, amps, sun, light bulbs, hair dryer, video games Sound Energy Sound Energy: energy that vibrating objects transmits through the air Examples: vocal chords, guitar strings, musical instruments Nuclear Energy Nuclear Energy: comes from changes in the nucleus of an atom; most intense form of energy; dangerous to humans Examples: sun, nuclear power plants, nuclear warfare