Unit 305 Session 2 Density

​THE PROPERTIES OF MATERIALS

​There are many materials that you, as a plumber, will deal with in your working life.

Each one will have different characteristics, such as weight, melting point, density and strength.

It is important that we know and understand the materials we work with to ensure that the correct material is used for a given application.

Here, we will investigate some of the many different materials we use, together with their working properties and their uses.

​Density

Open Ended

Why do you think the Coke sinks but the diet coke floats?

​Density

​Materials of the same size and shape can have a completely different weight because their molecules are more tightly packed together. ​ 

​To understand density we first need to look at 2 other things:

1. Mass
2. Volume

Open Ended

What do you think Mass is?

​Mass

​The simple definition of mass is the quantity of matter within a given object.

​All matter (Objects) are made up of atoms, the more atoms contained in an object, the more mass it has.

For example if we take a block of lead and compare it to a block which is the same size made of sponge which do you think would contain the most atoms?

​We measure Mass in kilograms and multiples or fractions of the kilogram.

​Note Mass and weight are not the same.

Open Ended

What do you think Volume is?

​Volume

​A volume is simply defined as the amount of space occupied by any three-dimensional object.

​The formula for calculating volume is: volume = length x width x height

Fill in the Blank

So what is the volume of this cuboid?

​Relative density of solids, liquids and gases

​Relative density is the ratio of a substance's density to the density of a reference substance.

For liquids and solids, relative density is calculated by comparing the density of the substance to the density of water at its densest, which is at 4°C.

For gases, relative density can be calculated by comparing the density of the gas to the density of dry air, both at standard temperature and pressure. 

Relative density was previously known as specific gravity. 

​We say: water has a density of 1​ 

This means that any solid or liquid with a density of more than 1 will sink, and any solid or liquid with a density of less than 1 will float. ​ 

​ 

We say: air has a density of 1​ 

This means that any gas with a density of more than 1 will sink, and any gas with a density of less than 1 will rise. ​ 

Multiple Choice

Using the table in the picture, state whether the material below will float or sink.

Natural Gas

• Float

• Sink

Multiple Choice

Using the table in the picture, state whether the material below will float or sink.

Aluminium

• Float

• Sink

Multiple Choice

Using the table in the picture, state whether the material below will float or sink.

Cast Iron

• Float

• Sink

Multiple Choice

Using the table in the picture, state whether the material below will float or sink.

Polythene

• Float

• Sink

Multiple Choice

Using the table in the picture, state whether the material below will float or sink.

Propane

• Float

• Sink