The Nature of Energy
Energy Every change that occurs involves ENERGY Moving objects have energy You can tell an object has energy when it: Changes its environment Changes itself Energy Electrical – moving electrons Chemical – from bonds Thermal- heat
Energy Energy exists in many different forms It may look different, but it’s still energy. Examples: fire, movement, gasoline in a bucket
Energy Types Kinetic energy- energy in the form of motion Depends on mass and velocity of an object Increase in either mass or velocity = increase in energy KE =1/2 mv2 Units = kg*m2/s2 KE = ½ mv2 Velocity changes will impact KE more because velocity is squared.
Types of Energy Potential Energy – energy of position Energy in stationary objects and bonds Elastic Potential Energy – Energy of compression or stretching Chemical Potential Energy – Energy stored in bonds Gasoline, food, hand warmers http://www.youtube.com/watch?v=Jnj8mc04r9E&feature=related
Types of Energy Gravitational Potential Energy- Energy stored due to position above the surface of Earth Depends on mass of object, height of object above ground, and acceleration due to gravity GPE = m x h x a All energy – measured in units of Joules 1 J = 1 kgm2/ s2 Energy can be converted: As an object falls, GPE decreases and KE increases
Law of Conservation of Energy Energy cannot be created or destroyed. E is constant in universe Can only be transformed from one type to another Energy can be transformed into non-useful forms, like heat “Disappearing energy” – doesn’t disappear Is converted into thermal energy by friction
Demo #2 Question #1: Where is the energy come from? Question #2: How does this demonstration illustrate the Law of Conservation of Energy? Question #3: At what point in the pendulum's swing is its gravitational potential energy highest? Question #4: Describe the point at which the kinetic energy of the pendulum is highest.
Changing Forms of Energy Many devices convert energy from one form to another Electrical to thermal Mechanical to Electrical In Vehicles: Engine: Chemical Energy to Kinetic energy Spark plug: Electrical Energy converts gasoline’s chemical energy to thermal energy Thermal Energy causes gases to expand Expanding is mechanical energy, which moves parts of the car = kinetic energy
Conversions Between Forms of Energy Plants: light into chemical Uses E from sunlight to make bonds Mechanical energy – total KE and PE in a system ME = KE + PEG + PEe Amount of ME is due to: Position and Motion Can PE be converted into KE?
Pra
Practice problems for kinetic and potential energy What is the kinetic energy of a car with a mass of 500 kg and a speed of 5 m/s? What is the GPE of a person standing at the top of a ladder with a height of 15 meters? The person has a mass of 80 kg.
Practice continued… What is the kinetic energy of a child on a swing with a mass of 30 kg and a speed of 3 m/s? What is the GPE of a bowling ball with a mass of 1.5 kg and held 2 meters above the ground?
Resources Roller coaster Animation: http://www.physicsclassroom.com/mmedia/energy/ce.cfm http://www.youtube.com/watch?v=0ASLLiuejAo&feature=related