You have learned to measure the mass and volume of various substances. Now it is time to apply this knowledge in calculating density. Density is a comparison of the mass and volume of an object. In this activity you will be able to compare the densities of various objects. You may even try to use density to solve the problem of which kind of candy bar is the best value for your purchase.

Materials: (per group of 2-4 students)

• Wood block
• Ruler
• Calculator
• Paper towels
• Glass marble
• Beakers
• Water
• Balance scale
• Bite-sized Snickers® bars (optional)
• Bite-sized Three Musketeers® bars (optional)

Background Information:

• For this activity you need to understand how a balance works and know how to use it.
• Remember that volume of an object can be measured three ways.
• The volume of containers can be measured indirectly by filling them with water, then pouring the liquid into a graduated cylinder or beaker for measurement.
• You may use other materials that are not listed if you have permission from your teacher or the responsible adult.

Extension: You might compare the densities of regular and diet softdrinks in a plastic bottle or can. The different sweeteners usually have different densities.

Safety concerns: Be sure to keep all glassware safety rules. Remember not to put a stopper into any flask unless given direct instruction by your teacher. Follow all teacher direction about how to dispose of any materials.

Procedure

1. The densities of water, wood, glass marble, and candy bars must be found.
• The density of a material can be found by dividing the object’s mass by its volume.
• The formula is (density = mass divided by volume.)
2. To find the mass of an object:
3. Record the mass in the data table in grams
4. Find the volume of an object:
5. Calculate the density:
6. Record this density as g/mL in your data table.
7. Repeat these procedures for each of the other 5 objects

Data:

 Material: Mass (g): Volume (mL): Density (g/mL): Wood _________ g _________ mL _________ g/mL Water _________ g _________ mL _________ g/mL Glass marble _________ g _________ mL _________ g/mL Snickers bar (optional) _________ g _________ mL _________ g/mL Three Musketeers bar (optional) _________ g _________ mL _________ g/mL

Analysis:

1. Which object has the greatest density? Which object has the lowest density?
2. Make a bar graph of the densities that you have found. Draw a line across the graph on top of your water density bar. What relationships exist between objects that are below the line you have drawn and those objects whose graph is above the line?
3. If any object has a density less than water (below the line on the graph), what will that object do when it is placed in water?
4. If an object has a density that is greater than water (above the line on the graph), what will it do when it is placed in water?
5. Based on these observations, predict the densities (relative to water) of the following materials:
• ice
• rocks
• an aircraft carrier
• human
• gasoline
• oil
6. Based on density, which candy bar is a better value, Snickers® or Three Musketeers®?
Review science safety rules here.

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