11. The natural frequency of a spring can be reduced by reducing the weight of the wire. True_ False__.
12. For both shaft design and spring design, the running frequency should be at least two times lower than the first mode of natural frequency. True_ False__.
13. Considering the contact fatigue of a gear, the wear factor should be higher than the gear factor. True_ False__.
14. The Sines method and Zimmerli data were only applicable for torsional stress analysis. True_ False__.