1. Density:
* Density is a measure of how much mass is packed into a given volume. A rock's density tells you how heavy it is compared to its size.
* Water has a density of approximately 1 gram per cubic centimeter (g/cm³).
2. Floating vs. Sinking:
* If the rock's density is less than the density of water (1 g/cm³), it will float. This is because the rock will displace a volume of water equal to its own weight, making it buoyant.
* If the rock's density is greater than the density of water (1 g/cm³), it will sink. This is because the rock is heavier than the same volume of water, and it can't displace enough water to support its weight.
3. How to Test (without precise tools):
* Simple Test: Gently place the rock in a bowl of water. If it floats, it's less dense than water. If it sinks, it's denser.
* Visual Clues: Rocks like pumice or certain types of volcanic rock often have a porous structure, making them less dense.
4. More Accurate Measurement (with tools):
* Weigh the rock: Use a scale to find its mass in grams.
* Measure the rock's volume: You can do this by submerging the rock in a graduated cylinder filled with water and measuring the volume of water displaced.
* Calculate the density: Divide the rock's mass by its volume. The result is the density in grams per cubic centimeter (g/cm³).
Remember: The shape of the rock can also affect its stability in water. A flat, wide rock might float better than a small, round rock, even if they have the same density.
