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Central Force Problem

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Qualitative Behavior<br />

• Integrating the radial motion<br />

isn’t always easy<br />

• More often impossible…<br />

• You can still tell general behavior by looking at<br />

E<br />

V′ () r ≡ V()<br />

r +<br />

2<br />

l<br />

2mr<br />

2<br />

• Energy E is conserved, and E – V’ must be positive<br />

2<br />

mr<br />

= + V′<br />

() r<br />

2<br />

mr<br />

2<br />

• Plot V’(r) and see how it intersects with E<br />

2<br />

2<br />

2 ⎛<br />

l<br />

r<br />

= ⎜E−V()<br />

r −<br />

m⎝<br />

2mr<br />

Quasi potential including<br />

the centrifugal force<br />

= E− V′<br />

() r > 0<br />

E<br />

2<br />

> V′<br />

() r<br />

⎞<br />

⎟<br />

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