w-a 2x epeP8x d2x dx_πdpgx d 0= 元P8 dt2 4m m 4 元m T= 2元 2 2 2 d d 2 π t x mgx d Vmg = ⎥⎥⎦⎤ ⎢⎢⎣⎡ ⎟⎠⎞ ⎜⎝⎛ +− ρ x m gd t x 4 π d d 2 2 2 ρ −= 2 2 2 d d 2 π t x mx d gVgmg ⎟ = ⎠⎞ ⎜⎝⎛ −− ρρ m ρ gd ω π 2 = g m d T ρω 2π 4 π == x x o