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## What is energy?

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**Newton’s Laws**• An object in motion will stay in motion (or rest at rest) unless acted on by an outside force. (Inertia) • Force = mass x acceleration (Units: Newtons = kg x m/s2) • For every action there is an equal and opposite reaction.**Work**• Energy = ability to do work • Work = force exerted over a distance • W (or “energy”) = F xd • 1 Joule = 1 Newton x 1 meter • 4.18 Joule = 1.00 calorie**Power**• Rate at which work is done • Power = Work / time • Watts = Joules / seconds • SO… Energy can also be expressed this way: • Energy = Power x time • Joules = Watts x seconds**Consider:**• What does it mean to give electrical appliances a rating in watts? • What is a kilowatt? What is a killowatt-hour? • Why do we describe food in terms of calories?**Forms of Energy**• Kinetic energy = Energy of moving objects • KE = ½ mass x velocity2 • KE = ½ mv2 • Joules = ½ kg x (m/s)2 • Potential energy = Energy stored due to position or composition • PE = mass x acceleration due to gravity x height • PE = mgh • Joules = kg x m/s2xm**Consider:**• How do each of the following represent KE? • Heat radiating from a car • The sound of my voice • Muscles contracting • Light traveling to your eye**Consider:**• How do each of the following represent potential energy? • A book on the edge of a table • A slice of pizza • Two magnets near each other • An electrical outlet • A stretched rubber band**What is heat?**• Kinetic energy caused by atoms moving and colliding • Flows from warm body to cold body • Not the same as temperature**Temperature Scales**• ° F = (1.8 x ° C) + 32 • ° C = (° F – 32) / 1.8 • Both use freezing and boiling points of water as standards • Kelvin = ° C – 273 • 0 K = absolute zero**Specific Heat**• Ability of a material to absorb/lose heat • Q = mcΔt • Heat gained/lost = mass x specific heat x change in temp • If two substances have equal mass and equal change in temp., what does the amount of heat gained depend on?**Heat transfer**• Conduction – transfer due to atoms colliding or vibrating • Convection – transfer due to bulk movement of a fluid (gas or liquid) • Radiation – transfer due to electromagnetic radiations (uses electrical/magnetic fields instead of matter) • file:///Users/johnb/Desktop/lsps07_int_heattransfer/lsps07_int_heattransfer.html • How can these types of transfer work together?**1st Law of Thermodynamics:Conservation of Energy**• Energy cannot be created or destroyed but can be transformed • PE = KE • mgh = ½ mv2 • How can our examples of PE be converted into KE? Is the reverse also true? • Are energy conversions 100% efficient?**2nd Law of Thermodynamics: Entropy**• Statements: • Heat will not flow spontaneously from a cold to a hot body. • You cannot construct an engine that does nothing but convert heat to useful work. • Every isolated system becomes more disordered with time. (Entropy) http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf**Applications**• Can any system transfer energy with 100% efficiency? What does this mean in living systems? • How do we maintain order in systems (especially living systems)? • Where does energy go? Is it truly “lost”?**Back to the Sun – Nuclear Fusion**• High pressure and high temperature force atoms together • Mass converted to energy • Energy radiates into space • How do atoms relate to energy?