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Chapter 7

Chapter 7. Energy. Introduction. Universe is made up of matter and energy. Energy is the mover of matter. It has several forms. To understand this concept we will begin with a closely related physical concept. 1. WORK. Work = Force x distance or W = F . d Units - Joules (J)

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Chapter 7

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  1. Chapter 7 Energy

  2. Introduction • Universe is made up of matter and energy. • Energy is the mover of matter. • It has several forms. To understand this concept we will begin with a closely related physical concept.

  3. 1. WORK • Work = Force x distance or W = F.d • Units - Joules (J) • Pushing on a wall and wall doesn’t move (no work done on the wall)

  4. x

  5. 2. POWER Power = Work/time or P = W/t Units - J/s = W 1 hp 1 hp = 746 J/s = 746 W 100 W bulb = 0.1341 hp 250 hp engine = 186,450 W

  6. 3. MECHANICAL ENERGY • When work is done on an object, the object generally has acquired the ability to do work. • This is called energy and it has the same units as work. Two Types of Mechanical Energy Potential Energy Kinetic Energy

  7. Potential Energy • Energy of position or configuration • Dart gun – Balestra Other examples - Springs, bow, sling shot, chemical energy, and gravitational potential energy • The latter is E = mgh

  8. The potential energy of an object depends on a reference position. • It represents the work done against gravity to put the mass m in its position h above some reference position. • It is an energy of position.

  9. Kinetic Energy • It is an energy of motion. • It is a square law. • Total Work (work done by all forces acting on mass m) = DKE

  10. Note Work to Stop KE 0

  11. Work-Energy Theorem The net work done on an object is equal to the change in the kinetic energy of the object. Net Work = DEk

  12. 4. CONSERVATION OF ENERGY • Energy is always conserved • Energy lost due to friction is actually not a loss; it is just a conversion.

  13. Energy cannot be created or destroyed. • It may be transformed from one form into another, but the total amount of energy never changes. • Energy Conservation in Satellite Motion (Next slide)

  14. Perigees Hyperbola Parabola Circle Ellipse Ellipse Energy is conserved along all of these paths. Apogees

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