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Energy

Energy. Finally, formulas. Energy. So we can’t exactly define energy, but we know we can measure it in some different forms Kinetic Gravitational Elastic (springs) Thermal (heat) Electrical Magnetic Chemical. Measuring Energy. Energy is measured in the units of Joules (J)

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Energy

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  1. Energy Finally, formulas

  2. Energy • So we can’t exactly define energy, but we know we can measure it in some different forms • Kinetic • Gravitational • Elastic (springs) • Thermal (heat) • Electrical • Magnetic • Chemical

  3. Measuring Energy • Energy is measured in the units of Joules (J) • 1J = 1 kg * m2 / s2 • So • J/kg = m2/s2 • J/(m2/s2)= Kg • N*m = J

  4. Gravitational Potential Energy • The energy of height • On Earth: • GPE or Eg = m * g * h • m = mass in kg • g = 10m/s/s (gravitational constant) • h = height in m

  5. How Much Energy does a 5kg object 2m off the ground have? • GPE = m * g * h • GPE = 5kg * 10m/s/s * 2m • GPE = 100 kg * m2/s2 • GPE = 100 J

  6. Kinetic Energy • The energy of movement • KE or Ek = ½ m * v2 • m = mass in kg • v = velocity in m/s

  7. How much kinetic energy does a 10kg car moving 4m/s have? • KE = ½ * m * v2 • KE = ½ * 10kg * (4m/s)2 • KE = 5kg * 16 m2/s2 • = 80 kg * m2/s2 • = 80J

  8. Elastic Potential Energy (Eel) • Aka Spring Potential Energy (SPE) • Eel = ½ k * x2 • k = spring constant (how hard the spring is to compress) in N/m • x = how much the spring is stretched/compressed in m

  9. How much Eel does a spring (constant = 100N/m) stretched 2m have? • Eel = ½ * k * x2 • Eel = ½ * 100N/m * (2m)2 • Eel = 50N/m * 4m2 • Eel = 200N*m • = 200J

  10. Energy • So we can’t directly define or measure energy • But we can calculate the total amount of energy by adding all of the different forms • Total Energy = Ek + Eg + Eel + (other forms of energy)

  11. Show your work! • On the classwork and homework and for ever and ever in physics you need to show your work • Allows you to do harder problems than the ones you have been given

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