单词	lever
释义	lever A simple machine consisting of a rigid bar pivoted about a fulcrum. The mechanical advantage or force ratio of a lever (the ratio of load to effort) is equal to the ratio of the perpendicular distance of the line of action of the effort from the fulcrum to the perpendicular distance of the line of action of the load from the fulcrum. In a first-order lever the fulcrum comes between load and effort. In a second-order lever the load comes between the fulcrum and the effort. In a third-order lever the effort comes between the fulcrum and the load. See illustrations. Levers
随便看	radiant energy radiant exitance radiant flux radiant intensity radiation radiation belts radiation damage radiation pressure radiation temperature radiation units radiationless decay radiative collision radical radio radio astronomy radio frequencies radio galaxies radio interferometry radio source radio star radio telescope radio transmission radio window radio-opaque radioactive age

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