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Transcript
Describing energy CHAPTER 4 SECTION 2 Change requires energy Calorie is a unit of energy Your body uses food as energy The calorie is a unit of heat used to indicate the amount of energy that foods will produce in the human body 1 calorie is 4.1868 J Energy is the ability to cause change Energy can also be described as the ability to do work, therefore energy can be measured with the same units as work, or joules ( J ) As a soccer player swings his leg to kick a ball the players leg has energy, the players leg and foot cause change when the ball is kicked. If the players leg does 250 J of work on the ball, then 250 J of energy are transferred from the leg/foot to the ball. The leg/foot and soccer ball are a system. A system is anything around you which you can imagine a boundary. Systems can be single objects, soccer ball, or the solar system When one system does work on a second system, energy is transferred from the 1st to the 2nd Different forms of energy Mechanical Electrical Chemical radiant Energy is energy, just in different forms Chemical energy and mechanical energy are both energy just in different forms Gasoline is chemical energy, rays from the sun are energy but both are still just energy. Kinetic energy – energy of motion 1 2 Kinetic Energy = mass x velocity squared 1 2 K.E. = mv2 Kinetic energy in joules, mass in kg, velocity m/s Problems pg 116 Potential energy Potential energy is energy that is stored due to the interactions between objects Ex: a rock at the top of a hill, fruit hanging from a tree, objects connected by a compressed spring or stretched rubber band Elastic potential energy Elastic potential energy is energy that is stored by compressing or stretching an object Chemical potential energy Chemical potential energy is energy that is due to chemical bonds When chemical bonds are broken energy can be released, during chemical reactions energy also can be released, in the form of light energy, thermal energy, or radiant energy Gravitational potential energy Gravitational potential energy is energy that is due to the gravitational forces between objects. Equation: GPE ( J ) = mass (kg) x gravity (N/kg) x height (m) GPE = mgh Problems and section review Qs pg 119
