"which is heavier, a pound of feathers or a pound of lead? " the answer is obvious, of course, since a pound of feathers and a pound of lead both weigh the same—one pound. however, there is clearly something different about a small piece of lead and a large bag of feathers, even though they weigh the same. the relationship between the lead and feathers is expressed by the physical property called density. density is defined as the ratio of a substance’s mass to the volume it occupies. density (g/ml) = mass ( volume (ml) in this laboratory investigation, you will be using the physical property of density to determine the identity of different substances. you will also calculate the percent error, which is a comparison of the differences between the measured value and accepted value. percent error can be determined as follows: % error = ⏐measured value – accepted value⏐ x 100 accepted value objectives when you have completed this activity, you should be able to: observe the chemical and physical properties of substances to interpret the structure of and changes in matter. materials balance metric ruler 100 ml graduated cylinder 250 ml beaker rectangular solid (child’s block) metal sample (fishing weight)