Def: The mass of an object is the amount of matter in it.

 

1,000g = 1kg

 

Def: The density of a substance is the mass of 1cm2 of that substance.

 

Density = Mass

             Volume

 

The unit of density = g/cm3 or gcm-3

 

Archimedes’ Priciple: A body will float in a fluid if it is less dense than the fluid.

 

Heating air makes it less dense, this is why a hot air balloon floats.