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ENERGY

ENERGY. ENERGY. Basic Ideas about Energy: It is the property of an object that gives it the ability to cause change It can be neither created nor destroyed, i nstead it is transferred from one type to another: thermal, chemical, nuclear, electrical, etc

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ENERGY

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  1. ENERGY ENERGY

  2. Basic Ideas about Energy: • It is the property of an object that gives it the ability to cause change • It can be neither created nor destroyed, instead it is transferred from one type to another: thermal, chemical, nuclear, electrical, etc • Units for ENERGY are kg•m2/s2= Joule (J) • It takes energy to get something done • i.e, Energy is converted when Work takes place ENERGY

  3. POTENTIAL ENERGY Potential Energy = the stored energy of an object as a result of the position ENERGY We are going to learn about two types of PE…gravitational potential energy and elastic potential energy!

  4. Gravitational Potential Energy (GPE) • This type of PE is when an object’s stored energy is the result of its vertical position (height) • It is dependent on mass and height • Formula is Peg = mgh ENERGY • Peg = mgh • Peg = (75)(9.8)(4) • Peg = 2,940 J Energy is a scalar quantity, so direction is unimportant!

  5. EXAMPLE: A 2 kg book sits on a bookshelf 2.1 m high. What is the potential energy of the book relative to the floor? ENERGY Peg = mgh Peg = (2)(9.8)(2.1) Peg = 41 J

  6. Elastic Potential Energy • Stored energy in elastic materials as the result of their stretching or compression • Ex: springs, bungee cords, bow and arrows ENERGY

  7. Elastic Potential Energy F = -kx In this equation, the force used to stretch or compress the object (F) is equal to the amount of deformation/how far stretched or compressed (x) multiplied by the spring constant (k) PEs = ½kx2 k = spring constant x = amount of deformation ENERGY

  8. PEs Example The staples inside a stapler are kept in place by a spring with a relaxed length of 0.115 m. If the spring constant is 51 N/m, how much potential energy is stored in the spring when the length is stretched to 0.150 m? ENERGY PEs = ½kx2 PEs = ½(51)(0.150-0.115)2 PEs = ½(51)(0.035)2 PEs = .031 J

  9. Kinetic Energy • Kinetic energy is the energy of motion • It is dependent on mass and velocity • Formula is KE = ½mv2 ENERGY

  10. KE Example Determine the kinetic energy of a 625 kg rollercoaster cart that is moving with a speed of 18 m/s. ENERGY KE = ½mv2 KE = ½(625)(18)2 KE = ½(625)(324) KE = 1.05 x 105 J

  11. Relationship Between PE and KE • As an object moves, the amount of PE and KE may shift back and forth ENERGY

  12. Graphing • In a Force (F) vs. Deformation (x) graph, the slope of the line is the Spring Constant (k) ENERGY You can reason this out since slope = y2-y1/x2-x1 (which is the same as dividing Force by Deformation) and the rearranged equation for F = -kx would then be k = F/x Spring Constant (k)

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