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Chapter 4

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The nature of energy Energy: The ability to do work or cause change All energy involves either motion or position Where are we using energy right now?

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What are some types of energy? Thermal energy : The total kinetic energy of particles that make up an object Chemical energy: The energy of a compound changes as the atoms are rearranged to form new compounds. Electrical energy: the energy of moving electrons Sound energy: The energy of vibration Light energy: The energy of vibration of electrically charged particles Nuclear energy: the energy associated with changes in the nucleus of an atom

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Mechanical NRG Mechanical energy is the total amount of potential and kinetic energy in a system

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Kinetic energy Kinetic energy is energy in the form of motion.

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Potential energy is stored energy because of position or shape

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Energy transfer

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How to calculate kinetic energy: Kinetic energy = ½ (mass x velocity 2 ) or KE = ½ (mv 2 ) Labeled as Joules Joule is expressed in N x m or 1 Joule= 1 kg * (m/s)2 What is the kinetic energy of a 45 kg object moving at 13 m/sec? mass = 45 kg velocity = 13 m/sec KE = ½ (mv2) So… KE = 1/2 (45 kg)(13 m/sec)2 Solving the equation gives a kinetic energy value of 3802.5 J

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Calculate Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s. KE = (0.5) * (1000 kg) * (20 m/s)2 KE = 200 000 Joules If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? KE = 0.5*1000 kg*(40 m/s)2 KE = 800 000 Joules As your speed doubles your kinetic energy quadruples.

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Gravitational Potential Energy Grav. Potential energy = weight x height Or….. PE = w x h Elastic Potential energy: energy stored by compressing or stretching something A 37 N object is lifted to a height of 3 meters. What is the potential energy of this object? weight = 37 N height = 3 meters Solving the problem gives a potential energy value of 111 J.

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