钟摆的模型：一个无质量竿子尾部的质点。（解题领域知识）
阻尼（摩擦）与钟摆角速度具有比例关系。（离散数学领域知识） |—-| ||| θ = angle of pendulum ( 0 = vertical)
ω = θ’ = angular velocity
R = length of rod
m = mass of pendulum
g = gravitational constant
b = damping (friction) constant
A = amplitude of driving force
k = constant related to frequency of driving force
t = time in seconds