# Chapter 1 - Questions and Problems: 1.21

Mass is the amount of matter present in a substance. It is constant. Weight is the force exerted by gravity on a substance, and it may vary. Weight on the moon = 27.7 lb.

#### Work Step by Step

Weight on the moon = Weight on the earth $\times$ Gravity of the moon relative to the earth = $168 lb\times 0.165$ = 27.7 lb

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