Density: teacher workshop activity (written in 2003 by Don Yost)
Teacher notes follow, for a student lab
Using a balance, mass one of the 1 cubic centimeter metal cubes. (Some of these cubes may not
be exactly 1 cc., but for this exercise, assume they are. We can correct our readings with more
accurate measurements later).
1. How much is its mass?
2. How much is its volume? (remember, it’s a 1 cc. cube)
3. So, what is the mass of 1 cc. of this metal?
The answer you wrote on #3 is the mass of 1cc. The mass of 1 cc of material is often called “the
density” of the material.
“Density” is the mass of one cubic centimeter, so the units of density are: grams per cubic
centimeter. A density of 4 gm/cc would mean that the mass of 1 cc. of that material would be 4
gm. Find the mass of the other cubes supplied.
4. Using the example above, what are their densities?
Mass one of the 1 cc plastic cubes.
5. What is its mass?
6. What is its density?
Now connect 2 of the plastic cubes together. Carefully mass them with a balance.
7. What is the mass of the pair?
8. What is the volume of this group of blocks?
9. With the information in (7) and (8), how could you find the mass on one of these blocks?
Now connect 10 of these blocks together. Mass this group with a balance.
10. What is the mass of this group?
11. What is the volume of this group of blocks?
12. With the information in (10) and (11), how could you find the mass of one of these
blocks?
If you have a 10 cc. object and want to find the mass of one cc, what do you do? That's right, you
divide the big mass by 10 to find the mass of one. Go back and check your answer to question
#12. Now make a group of 5 blocks.
13. How much is its mass?
14. What is its volume?
15. What is the mass of one cc? (its density)
In other words, to find DENSITY: find the mass of an object and divide that by the volume, so
that you can find the mass of one cc. of the material. Division is just a way of finding the
number of 1cc blocks that are in a larger object.
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As an example, suppose the mass of some slime is 50 gm, and it has a volume of 5 cc. To find
the mass on one cc of slime (its density), we divide the mass by the volume: 50cm/5cc = 10
gm/cc. We now know that a one cc block of slime would mass at 10 gm. We know its density is
10 gm/cc.
16. What is the density of glop if a 8 cc block of it masses 24 gm.?
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DENSITY: teacher notes (written in 2008 by Don Yost)
Apparatus
Set of 1cc cubes of different material (Boreal)
Two different sized objects of same material
Cuisenaire rods
Interlocking plastic 1cc cubes
Electronic balances
Pre-lab discussion
Density is sometimes thought of as how tightly stuff is squeezed into some object. Imagine a
pound of feathers, a pound of wood, and a pound of iron. If I put each in black plastic wrap so
you couldn’t see what was inside, how could you tell which was which?
Feathers are not very dense, so it takes a lot of them to make a pound. Iron is very dense, and so
it doesn’t take much to make a pound. Bread isn’t very dense, a pound is reasonably large.
Smash the bread loaf into a small wad, would it still weigh a pound? Would it be just as dense as
it used to be?
Mass the two samples and ask why they have different mass. Students will refer to size. Since
size seems to matter, then if we wish to compare different materials, it’s only fair to keep the
masses the same. We have 1cc samples of different materials to compare.
Since we are only dealing with 1cc samples, we need to include this information in the
measurement label. One way is to label each measurement as gm for every cc or gm/cc.
This measurement of 1cc is called “density”
Lab performance notes
Students should consider density to be the mass of a unit volume. In this case, the unit volume is
1cc. Students should conclude that to find the density of an object with a larger volume than one
cc, they need to measure the mass of the object, and then find how many one cc. cubes would fit
into that object. Do not give them density = mass/volume yet. See if you can guide them to this
representation.
Lab
Find the mass of the 1cc samples, record them and be sure to label the mass of 1cc as “density in
gm/cc”
Post-lab discussion
Teacher masses 2 1cc cubes. “If this is the mass of two cubes, could I tell the mass of only one
without measuring it? Repeat with 5 cubes and with 10 cubes; can you give a way of finding the
mass of one cube (density) if I give the mass of more than one cube?
Second lab
Compare several different sized objects.
Give several Cuisenaire rods (do not include the single cc) and have students find and graph
volume vs. mass.
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Lab performance notes
Students should note that the slope of a mass vs. volume graph is the density. They should also
note that looking at the graph; they can determine the mass of a single cc cube even though they
did not actually measure one.
Post-lab discussion
Students should find volume linear with mass. Using graph, determine
y = mx + b. Mass the 1cc sample and compare with the value of the slope, m. Students derive:
mass = density x volume or density = mass/volume.
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