T=2πL‾gT=2 \pi \sqrt{\frac{\underline{L}}{g}}T=2πgL
T1=L1L2×T2T_{1}=\sqrt{\frac{L_{1}}{L_{2} \times T_{2}}}T1=L2×T2L1
T2=T1L2L1T_{2}=T_{1} \sqrt{\frac{L_{2}}{L_{1}}}T2=T1L1L2
L=gT24π2L=\frac{g T^{2}}{4 \pi^{2}}L=4π2gT2