The concept of the representative elementary length (REL) and its coordination meaning are presented for the first time.
本文首次提出代表单元尺度(REL)概念及其协同学意义。
The elementary unit of length is the "meter", it's common knowledge.
长度的基本单位是“米”，这是常识。
A variable length simple pendulum model is introduced, elementary analysis and perturbation analytic solution of nonlinear differential equation for parametric resonance are presented.
采用可变长度单摆的力学模型对秋千振荡给出初等分析，采用微扰近似法导出了秋千的非线性参数共振解析解， 并进行了讨论。
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