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Energy

Energy. February 17, 2012. Review of Quiz C - Fields. Organization of Part D. Chapter 12 - Gravitational energy Chapter 13 - Electric energy Chapter 14 - Nuclear energy. Kinetic energy. Conservation of energy.

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Energy

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  1. PHYS132 Spring 2012 Energy February 17, 2012

  2. PHYS132 Spring 2012 Review of Quiz C - Fields

  3. PHYS132 Spring 2012 Organization of Part D Chapter 12 - Gravitational energy Chapter 13 - Electric energy Chapter 14 - Nuclear energy

  4. PHYS132 Spring 2012 Kinetic energy

  5. PHYS132 Spring 2012 Conservation of energy • Consider situations where the kinetic energy of an object changes. Where did the energy go? Where did it come from? • Every increase in one type of energy must be accompanied by a corresponding decrease in some other type(s) of energy • That way, the total amount of energy remains the same Conservation of energy

  6. PHYS132 Spring 2012 Identify which energy types are increasing and which are decreasing • ①A brick is sliding across the floor and, due to friction, comes to rest ②. • ①Two bricks are sliding toward each other on a frictionless floor when they collide and come to rest ②. • ①A brick is sitting at rest on the floor when someone comes up to it and kicks it, making it move ②. • ①I drop a rock from rest, and it speeds up as it falls ②. • A child is bouncing on a trampoline. Compare the situation when ① the child is motionless at the top of the motion with when the child is motionless at the bottom ②.

  7. PHYS132 Spring 2012 Properties of gravitational energy • Gravitational energy is associated with the system of objects (like a rock and the Earth) • The gravitational energy of a system decreases when the objects come together Why?

  8. PHYS132 Spring 2012 Infinite separations Q: Suppose I am so far from the Earth that the Earth no longer exerts a (measurable) force on me. If I move one meter toward the Earth, does the gravitational energy associated with the Earth and me change? • The gravitational force decreases as the objects separate, eventually it becomes zero. • The gravitational energy increases as the objects separate, eventually it becomes… Zero!

  9. PHYS132 Spring 2012 Infinite separations

  10. PHYS132 Spring 2012 Predicting changes • Suppose we want blast a 2-kg rock into space (from the surface of the Earth; radius = 6.37×106 m; mass = 5.9736×1024 kg) so that it comes to rest in some other galaxy (far, far away). How much energy do we have to provide to the Earth/rock system? • 1.25×108 J

  11. PHYS132 Spring 2012 Predicting changes • Suppose we drop a 2-kg rock from a location 1.7371×106 m above the surface of the moon (the moon radius is 1.7371×106 m; mass = 7.349×1022 kg). How fast is it going just before it hits the surface of the moon? • 1680 m/s

  12. PHYS132 Spring 2012 For Monday • Read chapter 12 • Submit “reading review” question on chapter 12

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