河想 =-品{Xl B.Energy Method vi.idds aWm i=o a形 01 λ=constant =constant 本d战=0 →5 f=0 w.ds ∫id -cons tant 1=L 入 w府=z λ2 5-w/ ah=constant -(e 6.641,Electromagnetic Fields,Forces,and Motion Lecture 13 Prof.Markus Zahn Page 2 of 146.641, Electromagnetic Fields, Forces, and Motion Lecture 13 Prof. Markus Zahn Page 2 of 14 ( ) ( ) 2 2 1 dL = 2 d L λ ξ ξ ξ ( ) = 1 d 2 1 2 d L ⎡ ⎤ − λ ⎢ ⎥ ξ ξ ⎣ ⎦ B. Energy Method ξ ξ λ ξ + ⇒ λ− ξ m m d d dW vi = i = f dW = id f d dt dt dt m m =constant W W , i= f = = constant ξ ξ ∂ ∂ − ∂λ ∂ξ λ 0 ξ λ= ξ= − ξ+ λ m ∫ ∫ 0 cons tan t W = f d id ( ) i = L λ ξ ( ) ( ) ξ = λ λ λ ξ ξ ∫ 2 m cons tan t W= d= L 2L ( ) m 2 cons tan t W 1 d f= = 1 2 d L ξ λ = −∂ ⎛ ⎞ − λ ⎜ ⎟ ∂ξ ξ ξ ⎝ ⎠