Here is a sealed tub of ice. Soon it will be a puddle of water inside the tub. Will it then weigh more, less, or exactly the same?

Hands up your guess.

When ice melts, does the amount of material change, or just its shape?

Each group has a sealed tub of ice. If the class shares one balance, we weigh every tub together at the front bench. Read the prediction on the card below and decide whether you agree.

One step on the card asks your group to test one more thing, using only the kit already out. Your teacher will give you three ideas to choose from. Say what you expect before you try it.

While your tub melts, watch the clear bag of warm water. The water turns into an invisible gas (water vapour), then back into tiny droplets on the cold side. It is the same water, still trapped in the bag.

The particles in your tub are far too small to see, so the screen gives you a model of them instead: one material in a container, with the temperature in your hands. The state name only appears after you have watched what the particles do, so watch first and read the name second.

Now finish your Investigation Journal page on your own, answering the questions on the board.