This document discusses different measurement units and concepts including distance, mass, volume, density of liquids, and density of irregular solids. It explains that the meter is the basic unit for measuring distance, with millimeters, centimeters and kilometers as other common units. Mass is measured in grams using a balance and remains constant. Volume is measured in liters using a beaker or graduated cylinder. The density of a liquid is its mass per unit volume measured in grams per milliliter, with water having a density of 1 g/mL. An object's density determines if it floats or sinks in a liquid. Density of an irregular solid can be found using water displacement by measuring the volume of water before and after placing the object in.