SUMMARY OF LESSON 3
Section 1. Introduces the metric or SI unit system. A decimalized system in units of ten.
Section 2. Density and relative density
The weight of a body is the force of attraction between the body and the earth; the mass depends on what and how much material is present in the body.
Units of mass include grams, kilograms, and tons.
Volume is the size of a body in cubic measurement.
Units of volume include cubic centimeters, milliliters, liters, cubic meters.
Density = Mass/Volume (mass divided by volume)
Units of density g/m3
Density of water = 1 g/m3
Density of coal = 1.3 g/m3
Density of shale = 2.4 g/m3
Relative Density = Density of Substance / Density of water
Or Mass of Substance / Mass of Same Volume of Water
Relative Density of water = 1.0 Same
Relative Density of coal = 1.3 numerically
Relative Density of shale = 2.4 as density in g/m3
Relative density has no units: it is the ratio between the density of a material (eg coal) and the density of water.
Coal sinks in water because relative density of coal is greater than relative density of water.
Wood floats in water because the relative density of wood is less than the relative density of water.
Section 3. Relative density, ash content and calorific value of coal
Ash content of coal (relative density 1.3) is very low – say 4%
Ash content of coal (relative density 1.4) is higher – say 13%
Ash content of very inferior coal (relative density 1.6) is much higher – say 31%
Ash content of shale (relative density 2.4) is very high – say 85%
Throughout the range from clean coal to shale, ash content increases steadily with increase in relative density.
Ash lowers calorific value of coal.
The higher the relative density of coal, the lower the calorific value – therefore lower price.
Section 4. Bulk density of coal
Bulk density of coal is the mass of unit volume of coal in the loose state.
Bulk density of coal is about 800 – 900, kg/m3, or 0.8 – 0.9 g/m3 . Units of bulk density are as for density g/cm3 , kg/m3 , and t/m3. Bulk density is useful, eg estimating stocks and bunker capacities and can be used in some machines to give an ash content trend in coal but this will be discussed in a later lesson.