Density is defined as the mass of an object divided by its volume. It is a property of the material from which the object is made, and doesn't depend on the shape or size of the object. Different materials have different densities, so we could tell butter from margarine or zinc from iron by measuring the density.

We can also define the weight density, which is the weight of the object (in newtons) divided by the volume (in cubic meters). For people living on the surface of the earth, 1 Kg weighs about 9.8 N; the density and the weight density give the same information in different units.

The cubic meter is not a very popular unit for measuring volume, because it is so big (it's slightly bigger than a cubic yard, which is only used to measure concrete!). More commonly we use the liter (which is 1/1000 of a cubic meter) and the cubic centimeter (which is 1/1,000,000 of a cubic meter.

• Determine the weight density (or just the density, if you prefer) of water, by putting a measured volume of water in a plastic bag and weighing it.
• Determine the weight density of a wood block, by calculating its volume (length x width x height -- all measured in meters) and weighing it.
• Another way to determine the volume of an object is to put it in a cup with water, fill the cup to the very brim, fish out the object (without spilling too much water!), and seeing how much water has to be added to again fill the cup. Measure the density of something this way.

Check the box when you are done: 

Weighing things under water