Energy Unit Adapted from Motion, Forces, and Energy textbook Copyright 1997 Prentice-Hall Inc.
What is Energy? What is energy? Energy is not matter. Matter is anything with mass and volume We now know how to change matter into energy though. How? We live in an ocean of energy. Energy is all around us, we are surrounded.
Energy Energy: The ability of something to cause change The ability to do work Measured in joules (j) Unit: Energy (j) same as work (j)
5 Forms of Energy 5 forms of energy: 1. mechanical 2. heat 3. chemical 4. electromagnetic 5. nuclear
Mechanical Energy Mechanical Energy Energy associated with motion
Heat Energy The internal motion of the atoms is called heat energy. The faster the atoms move the more heat energy they have. Rub hands together mechanical to heat
Chemical Energy Chemical Energy Energy required to bond atoms together. bonds are broken, chemical energy is released
Electromagnetic Energy Electromagnetic Energy Moving electric charges
Nuclear Energy Nucleus -(protons and neutrons) nucleus splits, nuclear energy is released in the form of heat and light energy
Potential Energy Potential Energy (PE): Stored energy due to position Examples: rock on a cliff, battery, food, gasoline, stretched rubber band, apple hanging in a tree
Elastic Potential Energy Elastic PE: Energy stored by something that can stretch or compress (ex. rubber band, spring) Ex: shoot an object with rubber band. Farther you stretch the rubber band, the faster the object travels, therefore greater KE.
Elastic Potential Energy Do rubber bands have energy to do work? (un-stretched rubber bands no energy) Stretch rubber band—Does it have energy to do work? (stretched rubber bands have energy) Where is the energy when the rubber band is stretched? (it is in the rubber band) What happens to the energy when the rubber band is released? (it is converted into motion -- KE)
Gravitational PE Gravitational PE (GPE): Energy stored by objects that are above the earth’s surface (objects that can fall) Depends on mass, acceleration and height GPE increases with height
Gravitational PE GPE = mass gravity height GPE = m g h = weight height GPE = m (kg) 9.8 m/s 2 h (m) j = 1 Nm
Kinetic Energy Kinetic Energy (KE): Energy in the form of motion Depends on mass and velocity of moving object. Object in motion has ability to do work
Kinetic Energy KE = ½ mass velocity 2 KE = m V 2 2 (j) = (kg) (m 2 /s 2 ) 1 j = 1 kg m 2 /s 2
Kinetic Energy Double mass and you double energy Double velocity = 4 times the KE As velocity is squared, increase velocity and KE greatly increases. Which would hurt more? Double mass of bowling ball or double the velocity? Explain.
Roller Coaster PE: 354kJ KE: 0kJ V: 0m/s PE: 177kJ KE: 177kJ V: 26.2m/S h=70m Potential energy becomes Kinetic energy. h=35 m PE: 0kJ KE: 354kJ V: 37.1m/S PE: 0kJ KE: 354kJ V: 37.1m/S Kinetic energy can become Potential energy.
Energy analogy When energy is transferred, it can transform (change form) but it still remains energy. Analogy: How is energy like money? When money is transferred from one person or place to another it can change form (transform) but it still remains money.
Energy Transformations (ball) Demonstrate:how bounce height of ball becomes lower and lower each time it bounces. Have students infer why this happens. Each time the ball bounces, part of its energy is transformed into other forms of energy, such as thermal (heat) energy, sound energy and vibrations in the ground. In addition, some energy is absorbed by the ball. Therefore, it will never bounce as high as the initial drop height.
Energy Transformations Ex: A light bulb is a device that transforms electrical energy into electromagnetic (light) energy and thermal energy Chemical energy (coal)heat energy (burn to create steam) mechanical energy (steam is used to turn turbines) Electromagnetic energy (generates electricity) heat energy (blow drier, oven)
Law of Conservation of Energy The law of Conservation of Energy: Energy cannot be created or destroyed. It may be transformed from one form into another; however, the total amount of energy in the universe remains constant. (Transformers)
Law of Conservation of Energy Energy conversions occur without a gain or loss in energy Energy into a system = energy out of a system Due to friction, energy might seem to be lost, but it has changed into thermal energy..