Density is a measurement of how tightly matter is packed together in an object. It is calculated by dividing an object's mass by its volume. Ice floats in water because it has a lower density than water - ice has a density of about 0.9 g/cm3 while water has a density of 1 g/cm3. Hot air balloons and magma rise because they have lower densities than the surrounding air and rock, respectively. A ship will float if its overall density is less than that of water, which is 1 g/cm3.

1. BW: Why does ice float in water?

2. What is density? A material's density is defined as its mass per unit volume. It is, essentially, a measurement of how tightly matter is crammed together. The principle of density was discovered by the Greek scientist Archimedes . To calculate the density of an object, take the mass ( m ) and divide by the volume ( v ). This will give you the density in g/cm 3 .

3. Density Large ball – 0.53 g/cm 3 Medium ball – 1.05 g/cm 3 Small ball – 0.82 g/cm 3

4. The “bounceability” of a ball depends on its density, not on its mass or on how big the ball is.

5. Have you wondered why hot air balloons rise? When the air is heated, it becomes less dense until the balloon's total density is less than that of the atmosphere; A hot air balloon is literally floating on the denser, colder air. Why is cold air denser than hot air?

6. Do you know why volcanoes erupt? The main reason that magma rises to the surface to erupt at volcanoes is because it is less dense than the rocks that surround it.

7. A ship floating on water is a great illustration of the difference between mass and density. A ship must have a density of less than 1.0 g/cm 3 (the density of water), or it will sink. Ships have a large mass, because they are made of steel, but because they have a large volume, their density is less than 1.0 g/cm 3 . If enough mass is added to them such that their density goes above 1.0 g/cm 3 , they will sink.

8. You have a rock with a volume of 15cm 3 and a mass of 45 g. What is its density?

9. What is the mass of a 350 cm 3 sample of pure silicon with a density of 2.336 g/cm 3 ? Mass = density x volume x Mass = 2.336 g/cm 3 x 350 cm 3 Mass = 818 grams