MATERIALS:

Single pan balance (with loop or hook to suspend objects from the bottom of the pan)
Collection of different rock types and sizes (about golf ball size)
Beaker of water big enough to hold rock samples
Fishing line (for sling to hold rock samples suspended in the water)
Stand for the balance (a stack of books will work)

Figure 1: Balance set up.

PROCEDURE:

1. Record the type of rock for your first sample (if known), on the DATA TABLE.

2. Set up the balance and construct a sling from the fishing line to suspend the rock samples in the beaker of water. Zero your balance with the fishing line sling hanging from it (see figure 1).

3. Find the weight of the first sample (in air), by placing the sample on the balance and using the method prescribed for the type of balanced used. Record on the DATA TABLE.

4. Suspend the first sample from the fishing line sling with the rock completely immersed in the beaker of water (again see figure 1). Find the weight of the sample (in water), and record on the DATA TABLE.

CALCULATION:

5. Now calculate the density of the sample, and record your answer on the DATA TABLE. The formula is as follows:

Density =	(Weight in air) ---------------------------------------- (Weight in air) - (Weight in water)

Water has a density of 1 g/cm³, thus it buoys up anything within it by 1 gram per cubic centimeter of displacement. Because of this, the weight in air minus the weight in water, is equal to the volume of the rock sample in cm³.

REPEAT STEPS 1-5 for each rock sample.

DATA TABLE:
Sample	Rock type (if known)	Rock weight in air (g)	Rock weight in water (g)	Rock density (g / cm3)
1.
2.
3.
4.
5.
6.
7.
8.

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