Transcript ENERGY
ENERGY THE DRIVING FORCE What is Energy? • The ability to do work • The ability to cause change • Measured in Joules, just like work • Formula Symbol: E • as in E = mc2 Forms of Energy • Mechanical Energy • Describes energy stored and released according to function or force Forms of Energy • Electromagnetic Energy • Waves of mostly invisible energy • Includes light, radio waves, X-rays Forms of Energy • Chemical Energy • Stored and released in the bonds between atoms Forms of Energy • Nuclear Energy • Stored and released from the nucleus of an atom Forms of Energy • Thermal Energy • Heat in all its forms and flows Two descriptions of Energy • Potential Energy • Energy stored by position or condition • Kinetic Energy • Released energy or energy of motion Potential Energy • The easiest quantified PE is Gravitational PE • This is the PE stored in an object by its height above another reference point • PEGravitational = m g h Joules = kg●(m/s2) ●m Remember, g = 9.8 m/s2 Potential Energy, revisited… • Another form is Elastic PE • This is the PE stored in an object by its being disturbed from its natural state, • and how much it wants to return to that natural state • Good examples: • Springs, swings, pendulums, rubber bands Kinetic Energy • This is the KE released by an object by its motion • KE = ½ m v2 • Joules = kg●(m/s)2 Problems • A 3.0-kilogram toy dump truck moving with a speed of 2.0 m/s starts up a ramp. How high does the truck roll before it stops? • A 2.0-kilogram ball rolling along a flat surface starts up a hill. If the ball reaches a height of 0.63 meters, what was its initial speed? Problems • Find the potential energy of this roller coaster when it is halfway down the hill. • A 2.0-kilogram ball is tossed straight up with a kinetic energy of 196 joules. How high does it go? Law of Conservation of Energy • Energy can not be created or destroyed in normal reactions • Energy can be changed from one form to another • The total amount of energy must be the same before and after a change in energy • Most common energy conversion is from potential to kinetic energy • Gravitational potential energy of an object is converted to kinetic energy as the object falls. • Potential energy can become kinetic and vice versa. • Example: Pendulums Mechanical Energy in a Pendulum • Einstein’s famous equation • E = mc2 • m = mass • c = speed of light (3 x 108 m/s) • Shows that matter can be converted into energy and energy can be converted into mass.