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Published byFrederick Wilkinson Modified over 9 years ago
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Energy
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Energy is the ability to do work – Work is a transfer of energy Energy is measured in joules (J) – 1 joule = work done to move an object 1 meter by 1 N
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Kinetic NRG Energy of a moving object KE = 1/2mv 2 m = mass and v = velocity Square velocity first Double the mass, double the KE Double the velocity, quadruple the KE
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Potential NRG Stored energy Gravitational potential energy PE = mgh m = mass g = gravity h = height Greater the height, more PE Greater the mass, more PE
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Elastic potential energy – When an object is stretched or compressed – The more stretched, the more potential energy – The more compressed, the more potential energy
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Can there be kinetic energy and potential energy at the same time? – Yes! – Mechanical energy = KE + PE motion position Do you think energy can be created or destroyed? – No! – So the total amount of energy at the beginning will be the same at the end
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Forms of NRG Mechanical Thermal Chemical Electrical Electromagnetic Nuclear
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Mechanical Energy associated with motion and position Sum of potential and kinetic energy
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Chemical Energy stored in chemical bonds Bonds are broken, energy is released Examples – Chemical compounds, such as fuels – Food – Muscles
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Electrical Associated with electric charges Batteries convert chemical energy into electrical energy
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Electromagnetic Form of energy that travels through space in the form of waves Ex: light, X-rays, radio waves Often used for communication because they travel long distances
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Nuclear Energy stored in atomic nuclei Nucleus held by strong and weak forces (Large amount of PE) Fission (split nuclei) Fusion (combine nuclei)
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Thermal Potential and kinetic energy of atomic particles When atoms move faster, thermal energy increases and object becomes warmer
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Energy Conversions Energy can be converted from one form to another What type of energy conversion takes place when lighting a match? Chemical: rxns in muscles allow you to move the match Kinetic: match is moving Thermal: heat produced by friction Chemical: rxn on match’s tip triggered by thermal energy Thermal: heat produced Electromagnetic: light produced
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Conservation of Energy Energy cannot be created or destroyed, it can only be transferred Ex: Bike slowing – Kinetic NRG becomes thermal NRG – Friction between the bike and the ground/air – Lose kinetic NRG, gain thermal NRG, total NRG is the same Ex: Pole vault – KE Elastic PE Gravitational PE KE (KE + PE) beginning = (KE + PE) end
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Heat TOTAL amount of kinetic energy of particles Transfer of thermal energy because of temperature differences Moves from hot to cold objects
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Temperature AVERAGE amount of kinetic energy of particles Measure of how hot or cold something is Use a thermometer Celsius and Kelvin scales Absolute zero = 0 K Object heats up, particles move faster
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Thermal Contraction and Expansion If temp decreases, particles move slower and closer together, so object contracts If temp increases, particles move faster and farther away, so object expands
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Thermal NRG Absorption Depends on color, texture, and exposed surface area Absorb more than emit = temp increase Emit more than absorb = temp decrease Absorb and emit the same amount = thermal equilibrium
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Specific Heat Amount of heat needed to raise the temperature of one gram of an object one degree Celsius Lower specific heat = temp rises more when given a certain amount of energy Q = m x c x change in T or Q = mc∆T Q = heat gained or lost (J) m = mass (g) c = specific heat (SI unit: J/g ˚C) T = temperature (˚C)
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Conduction Transfer of thermal energy with no overall transfer of matter Objects must be touching to transfer heat
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Conductors – conduct thermal energy well – Most metals are good conductors because electrons move easily Insulators – conduct thermal energy poorly
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Convection Transfer of thermal energy when particles of a fluid move from place to place Convection current – Warm air rises – Cool air sinks
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Radiation Transfer of energy by waves moving through space All objects radiate energy – Heat lamps – Sun
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