INVESTIGATING DENSITY
EXPERIMENT SUMMARY
The student will explore how the concept of density includes two quantities: mass and volume.
LEARNING OBJECTIVES
The student will be able to:
• Identify relative densities of various materials.
• Calculate density if given mass and volume.
TIME ALLOCATION
2 hours, after collecting materials
MATERIALS REQUIRED
Tall glass or plastic cup (The taller-the better.)
Food coloring (Specific colors don’t matter.)
At least five (5) of the following: (about 10mL for the liquids….not much!)
• Tap water
• Rubbing alcohol
• Ping pong ball
• Dishwashing liquid
• Vegetable oil
• Plastic bead
• Plastic soda bottle top
• 100% maple syrup
• Corn syrup
• Lamp oil
• Cherry tomato
• Die (singular for dice)
• Metal bolt
• Popcorn kernel
• Honey
• Milk
Mechanism to take digital pictures for uploading.
BACKGROUND
Spend about 10 minutes visiting the pHET website using the density simulation. (See our Moodle page.)
Welcome back!
While mass is a measure of the amount of “stuff” in an object—its molecules and atoms, volume is the measure of how much space that “stuff” occupies. If the mass is spread out in a bigger space, we say that it is “less dense”. If that same mass is crammed into a smaller amount of space, we say that the substance is “very dense”.
Same volume (space) but the left has more matter (mass) in it.
The left picture depicts a higher density.
Mathematically, density is the ratio of mass to volume. D=m/V Its units are simply a combination of the units you used for mass and for volume, such as “g/mL” or “lb/gal”.
For the picture above, we could create an example like this:
The left picture has 27 masses in a 6 space. The right has 13 masses in a 6 space.
Therefore, the left has a density of 27/6 = 4.5 units, while the right has a density of 13/6 = 2.2 units
There are a couple of cool applications for this idea:
• Pure substances have a constant density. Therefore, if you have an unknown substance and can measure its mass and volume. You can calculate the density and look onto a chart and identify it. If you knew the substance and how much space it can occupy, you’ll calculate how heavy it is!
• Secondly, density determines what floats. Denser substances sink! This will be a unifying theme throughout our course. It explains why “hot air rises”, why cold water sinks, how minerals form in the Earth, and more!
For example, knowing the density of liquid mercury is 13.5 g/mL. You can use the table above to correctly predict that a piece of iron will sink in water, but it will FLOAT in mercury!
Hmmm….how does an iron ship float in water?
EXERCISE #1: RE-CREATE A DENSITY TOWER
PART A:
With as many of the items shown, create your own density tower. (Feel free to mix food coloring with your colorless ingredients like water and rubbing alcohol before you add them to the tower.)
POUR GENTLY! Keep your container slanted while pouring
Dispose of your tower in the sink with plenty of water. Fish out the solids, of course.
PART B:
Repeat your tower with ONE exception: change the order in which you add the substances. In other words, don’t add your items sequentially.
Hypothesis: (What do you think is going to be different about this tower than the first?)
POUR GENTLY!! Keep your cup slanted while you’re adding.
Order Substance
Added 1st
Added 2nd
3rd
4th
5th
6th

PART C:
Question 1: Summarize how the second tower compared to the first.
Question 2: What can you conclude about the densities of the substances at the top of the tower?
Question 3: Why is it incorrect to say that an object sinks because it is “heavier” than the others? (If you just used the word “heavy” or “light” in the question above, please correct it now.)
Question 4: Knowing that water is used to smother a fire, why should you never attempt to extinguish a grease fire with water? (Do NOT respond with the fact that water and grease don’t mix. This is a lab about density.)
EXERCISE #2: CONSIDER THE EFFECT OF TEMPERATURE
PART A:
Watch the video of me demonstrating with yellow and blue water in Erlenmeyer flasks. (See Moodle for the link.)
Make notes here:
PART B:
Question 1: Do not let the colors fool you. Why did the “fast” one happen? In other words, what made the top liquid “sink” into the bottom flask?
Question 2: Hypothesize whether the “slow” one will ever be totally green?
Question 3: Summarize the effect of temperature on density.
Question 4: Write 2-3 sentences relating density to planet formation and plate tectonics.

INVESTIGATING DENSITY EXPERIMENT SUMMARY The student will explore...