Physics 2211: Lecture 29

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Physics 2211 Lecture 29
Energy Diagrams
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Simple Pendulum
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Pendulum

energy
time
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Rather than a graph of Energy vs. Time, it is
often more convenient to make a graph of Energy
vs. Position. This is called an energy diagram.
Example If gravity is the only force present,
the potential energy is
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The particle is projected upward. The energy is
entirely kinetic
The energy is entirely potential at the turning
point.
The particle has gained potential energy lost
kinetic energy
The particle gains kinetic energy and loses
potential energy
The energy is entirely potential at the turning
point.
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Turning Points
Total E1
Total E2
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Here?
Or Here?
Or Here?
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The mass is released from rest. The energy Is
entirely potential.
The particle loses kinetic energy as
it compresses the spring.
The particle has gained kinetic energy. The
spring loses potential energy.
The point of maximum speed. the energy is
entirely kinetic.
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What kind of motion happens with this potential
energy curve?
Total E
KE
Point of Maximum Speed
Turning Point
PE
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What sort of motion is possible with this energy
diagram?
E
PE
TE
x
Classical Mechanics vs. Quantum Mechanics
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• The particle never reaches point A
• The particle bounces at point C
• The particle accelerates between D and C
• The particle decelerates between D and C
• The particle moves with constant speed

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A Look Ahead
force
force
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Potential Energy of an HCl molecule x
separation between H and Cl
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Recap
Energy Diagrams
Next Lecture
Energy Problems