例1 小明在一根均匀木杆的一端缠绕少许铅丝,使得木杆放在液体中可以竖直漂浮,从而制成一支密度计.将它放在水中,液面到木杆下端的距离为16.5cm,再把它放到盐水中,液面到木杆下端的距离为14.5cm.如果所用铅丝的体积很小;可以忽略,小明测得的盐水密度是多少?(2002年全国初物竞) Example 1 Xiao Ming winds a small amount of lead wire on one end of a uniform wooden rod, so that the wooden rod can be vertically floated in the liquid to make a densitometer. Put it in water, and the distance from the liquid level to the lower end of the wooden pole is 16.5cm, and then put it in salt water, the distance from the liquid surface to the lower end of the wood is 14.5cm. If the volume of the lead wire used is very small; can be ignored, what is the density of salt water measured by Xiaoming? (2002 National Birth Competition)