Liquids Liquids are identified as materials that: Have no definite shape Have a definite volume Are not easily compressed Are able to flow
l l l l
Fig. 9 Molecules in a liquid.
The particles in a liquid stay close to one another but can move past one another. Water is an example of a liquid.
Gases Gases are identified as materials that: Have no definite shape Have no definite volume Can be easily compressed Can flow
l l l l
Fig. 10 Molecules in a gas.
In a gas the particles move in all directions and they bounce off one another, causing the particles to spread out further and further. If the gas is held in a container the particles will bounce off the walls of the container as well as each other. The gas will spread out to fill the container. Water vapour is an example of a gas. Water vapour is invisible. There is usually water vapour
in the air. Every time you breathe out, water vapour is exhaled along with other gases. These gases are all invisible. In Fig. 11 the boy has just breathed
Fig. 11 Cold weather makes breath visible. 202
out into the cold air. His breath contained some water vapour. As soon as he breathed out, the water vapour, which is an invisible gas, cooled into tiny droplets of liquid water which are visible. The way that the water vapour turned into liquid water is called a change of state.
