University of California
Ucla K 6 Physics/astronomy: Mass, Weight, and Density
This website provides explanations of mass, weight, and density with directions for building simple scales and balances. Provided as encouragement to teach these concepts to young children, it offers a good review for older students.
CK-12 Foundation
Ck 12: Physical Science: Mass vs Weight
[Free Registration/Login may be required to access all resource tools.] Definition of weight and how to calculate the weight of an object.