Energy

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Chapter 7

• Energy

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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.

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1. WORK

• Work Force x distance or W F.d
• Units - Joules (J)
• Pushing on a wall and wall doesnt move
• (no work done on the wall)

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x

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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
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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
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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

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• 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.

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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

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Work to Stop KE
0

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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

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4. CONSERVATION OF ENERGY

• Energy is always conserved
• Energy lost due to friction is actually not a
  loss it is just a conversion.

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• 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)

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Perigees
Hyperbola
Parabola
Circle
Ellipse

Ellipse
Energy is conserved along all of these paths.
Apogees