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Energy The ability to do work. Unit = J Joule – relates to calorie 1 cal = 4.15 J Potential Energy • The stored energy of position. PE = mgh • The higher off the ground object is, the more potential it has to do work. Potential Energy • Potential Energy is energy of position. • An object gets potential energy from height, mass and gravity. • An object with potential energy has the potential to do work. This potential is only released if the object falls. • The energy is then transformed into energy of motion or transformed into work. Potential Energy • Potential energy helps us generate electricity in hydroelectric dams. When the water falls, gravity helps turn energy of height to electrical energy. Potential Energy Kinetic Energy • The energy of motion KE = ½ 2 mv • The faster an object is moving, the more ability it has to do work. • http://www.youtube.com/watch?v=qZ4FFWvZtyo Kinetic Energy • Kinetic Energy is energy of motion. • An object gets kinetic energy from its mass and velocity. • An object with kinetic energy has energy stored in motion. • When the object slows down the energy is released into potential energy (if going up) or some other kind of energy (like heat [thermal energy] in the brakes of car). Kinetic Energy Kinetic Energy The Law of Conservation of Energy • Energy cannot be created or destroyed. • It merely transforms from one form to another. Problems 10kg 1. What is the work done to lift a 10kg box to a height of 5m? 2. What is the box’s potential energy once it is there? 3. If the box is dropped, what is the PE halfway down (at 2.5m)? 4. A 8 kg cat is running 4 m/s. How much kinetic energy does it have? 5. A 4 kg bird has 8 joules of kinetic energy. How fast is it flying? Mechanical Energy • Mechanical Energy is the sum of all the kinetic energy and potential energy in a system. • Formula M = K + U • K = Kinetic energy • U = potential energy • Unit- J