Energy: Forms and Changes • The Nature of Energy • Kinetic and Potential Energy • Energy Conversions • Conservation of Energy • Physics and Energy
The Nature of Energy • Energy can be defined as the ability to do work. • Energy is often measured in Joules (J). • 1 Joule=1Kg-m2/sec2= 1 Nm • Energy comes in many forms. The main forms are: Mechanical, Heat, Chemical, Electromagnetic, and Nuclear.
The Nature of Energy(continued) • Mechanical energy is energy of motion. • Examples include a moving car and sound. • Heat energy is energy of internal motion (movement of atoms). • Friction is one cause of heat energy. • Chemical energy is stored in the bonds that keep molecules together.
The Nature of Energy(continued) • Electromagnetic energy is caused by moving charges. • Examples include electricity and light. • Nuclear energy is stored in the nucleus of an atom. • All stars (including our sun) run on nuclear energy.
Kinetic and Potential Energy • All of the types of energy just described fit into one of two categories of energy: Kinetic or Potential. • Kinetic energy is the energy of motion. • K.E.=(mass x velocity2)/2 • Kg x (m/sec)2=Kg-m2/sec2=Joule
Kinetic and Potential Energy(continued) • Potential energy is stored energy and is sometimes called energy of position. • For example, raising a bowling ball 1 meter above the ground gives it potential energy relative to the ground. • Gravitational Potential Energy (GPE)= Weight x Height. • Newtons x meters=Nm=Joule
Energy Conversions • Energy can be converted from one form to another. • This process can happen over and over again. • For example, I can convert the mechanical energy of rubbing my hands together into heat energy.
Energy Conversions(continued) • One of the most common energy conversions is Kinetic-Potential. • For example, by holding a 20 Newton bowling ball 1 meter above the ground, it has 20 Joules of gravitational potential energy. • By releasing the bowling ball, its potential energy is converted into kinetic energy as it gains velocity.
Energy Conversions(continued) • As the bowling ball speeds up towards the ground, its gravitational potential energy is reduced, and its kinetic energy is increased until the instant before it hits the ground. • At that point, the bowling ball has converted all of its GPE into kinetic energy, so that it now has 20 Joules of kinetic energy.
Conservation of Energy • The previous example shows how energy is always conserved. • In fact the Law of Conservation of Energy says that energy can neither be created nor destroyed by ordinary means. • Albert Einstein showed how energy can be converted into mass and mass into energy using his famous “E=mc2”
Conservation of Energy(continued) • The Law is consequently referred to as “The Law of Conservation of Mass-Energy.”
Physics and Energy • Understanding energy is critical to understanding the physical sciences. • Everything we have studied in MFE connects in some way to energy. • For example, the faster you move, the more momentum you have, the more kinetic energy you have, the higher your power, which means you consume energy faster.