Glass is a special material which can be melted into a liquid at high temperatures. It can then be blown or shaped. When the glass cools down, it stiffens and eventually becomes hard.

First broadcast:
9 October 2007

Students could investigate how the properties of substances change when heated. Before watching this clip students could be asked to describe the properties of sand and compare these with their properties of glass. Are there any similarities? Students could then watch the clip and note that sand is melted to make glass. What properties have changed? Students could consider how the newly formed properties make the glass useful for a particular purpose, and consider whether it could have fulfilled this purpose in its original form.

Students could then explore what happens to other substances when melted, such as chocolate, jelly or ice.