Why do some things float and other things sink?

• Can you explain why some things float and others sink?

• What evidence can you use to support your ideas?

• Do you have any evidence that is against your ideas?

• Do you agree with other groups’ ideas? What evidence can you think of to challenge them?

1. Let’s think back!

• What happens to the volume of the water when we dissolve salt in it?

• What happens to the weight of the water when the salt is added?

• What can you say about how heavy for its size salty water is compared to fresh water?

• How do you think the salt changes whether things will float or sink in the water?

2. Making salty water

3. Exploring salty water

• What difference do you notice when the water is salty?

• How can you explain this difference? What evidence can you use to support what you think?

• Do your ideas and rules for fresh water work for salty water?

• What is your group’s best explanation so far for why some things float and other things sink?

4. Plenary: eggstraordinary behaviour

• What are your ideas about why the egg floats in the middle of the liquid?

• What do you know about eggs in fresh water and in salty water?

• What is your best explanation for why the egg floats in the middle?

• Is there anything you would like to know that would help you decide?