Record your data
Make a table to record the mass and volume of the contents in each of the 24 bags.
Find the mass of each sample
Use the digital balance to find the mass (in grams) of the contents in each bag. To do this, you can find the mass of the entire bag and then subtract the mass of the plastic bag (assume it’s 5 grams), or you may use a more refined technique if you wish. Record the results in your table.
Find the volume of each sample
Use a method called water displacement to find the volume (in milliliters) of each bag’s contents. Partially fill a graduated cylinder with a known amount of water. Take the objects out of one bag, place them in the water, and note the new volume in the graduated cylinder. The difference is the volume of the objects you added in. Note the results in your table, blot the objects dry with paper towels, and then return them to their plastic bag. Move on to the next bag until you’ve found the volume of all 24 samples.
As you work, be sure the objects are completely submerged. If there’s not enough water, start over with more. If an object floats, gently push it down with a pencil or skewer until it’s just below the surface. Try not to push the pencil into the water too far—you don’t want to add its volume!
Create a graph of the results
Set up a graph on a large piece of paper with mass along the y-axis and volume along the x-axis. Scale the axes so the largest masses and volumes you measured will fit on the graph.
Assign a label color to each material (such as red for glass, blue for steel, yellow for PVC, green for wood), and stick a label at the appropriate mass-volume coordinates on the large graph for each of your samples. Do you notice a pattern in the data?
Use a ruler or straightedge to draw the best straight line through the dots that represent each of the four materials on the graph. Use 0,0 as the starting point of each line (when mass is zero, volume is zero).