Sample answers for questions that are answered offline are shown below.

Question 4

Liquid water – examples include: drinking, cleaning, irrigation, swimming, cooling, dissolving, diluting.

Ice – examples include: keeping food and drinks cool, first aid, skating, sculpting.

Water vapour – examples include: driving steam engines, electricity generation, humidifying.

Question 5

Although sugar appears to change shape when poured into a container, a closer look at the individual sugar crystals will reveal that they have actually not changed shape; it is simply that there are many solid sugar crystals moving independently of each other.

Question 6

Nike Air shoes contain air cushions in the soles. Since air is a gas, it is the compressibility of this gas which gives these shoes an additional cushioning effect.

Question 7

Carbon dioxide and dry ice are the same substance as they are made up of the same type of particle. Carbon dioxide is the gas form of the substance and dry ice is the solid form of the substance.

Question 9

(Answers for this question will vary.)

Extension Question 1

Fluids are substances that have a variable shape. They include liquids and gases. Liquids have a fixed volume, whereas gases have a variable volume.

Extension Question 2

Viscosity is a measure of a liquid’s resistance to flowing. Honey, syrups and oils are examples of viscous liquids. An increase in temperature results in these liquids becoming less viscous (more runny), and vice versa.

Extension Question 3

Polystyrene and rubber are solids but within them are many small air spaces (gas). When these materials are compressed, it is actually the air spaces which are being compressed, which is possible because gases are easily compressed.