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**Unformatted text preview: **W
F dr F dr F dr F dr
9 r2 r1 F dr
! "# WTOT
K>0 K W>0 or W<0 ! "# $ $ K<0 W=0 K=0 & ' ' $
+ ' $ " ( ( * " +
+ ) F
Coulomb force does negative work Potential energy increases
% x
+ + Analogy to gravity
m Exert force Fext = - Fg over distance h. Fext
m h Fg Work by me = Fext h = - Fgh = mgh = U
h 0 Fext d r h 0 Fg d r Ug h Ug 0 Ug Work by me - (Work by gravity) Change in Potential energy ( , A charge is released from rest in a region of electric field. The charge will start to move A) in a direction that makes its potential energy increase B) in a direction that makes its potential energy decrease C) along a path of constant potential energy F
x It will move in the same direction as F Work done by force is positive U = -Work is negative Nature wants things to move in such a way that PE decreases
34 7
6 ' FE " 7
$ ( FH 8
$ + E
./...

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