Volume (V) | Weight / Mass | Density
3. Density
Density is a property that describes how much mass an object has for a given amount of volume (a unit volume) . The dimensions of density are mass per unit volume (mass / volume or m/V). The different units we use are g/cubic cm or kg/cubic m. A cubic cm is simply a cube whose sides are each a centimeter tall. Use a ruler in the lab room to get an idea of how big a cubic cm is (pretty small). A cubic meter is a cube with each of its sides a meter tall. Use the meter stick at the back of the room to get an idea of how big a cubic meter is (it's big!)

If an object is not very dense, then we know we could pick up a big piece of it and it would not be very heavy. Cotton candy is something that is not very dense. Shaving cream is also not very dense. You could fill up an entire garbage bag with cotton candy or shaving cream and still pick it up (don't try this at home!)

If an object is dense, then we know a small amount of it would be heavy. Lead and gold are two things that are very dense. A brick is also very dense - they are small, but hard to pick up. If we filled the same garbage bag with brick, most of us would not be able to pick it up.

 

Archimedes and his experiment with buoyancy

Example

If the Earth has a mass of 6.0x1024 kg and a volume of 1.1x1021 m3 then its density is equal to 6.0e24 kg / 1.1e21 m3 which is 5.5e3 kg/m3. Notice that 6.0x1024 is the same as 6.0e24. Also notice that the units are in kg/m3. In this lab you will see density given in g/cm3. It is just a matter of converting one set of units into another. 5,500 kg/m3 is equal to 5.5 g/cm3. To check the conversion remember that there are 1000 grams per kilogram and 1,000,000 cm3 per m3. Therefore 5,500,000 g / 1,000,000 cm3 = 5.5 g/cm3.