We are learning about physical and chemical changes of matter. A physical change can change it's shape, or color but doesn't change what it is. A good test is that if a chemical change takes place, the object can't go back to it's original form.
Here are some examples:
The leaves had a chemical change, the dead leaves can't come back to life.
When the match is broken it's a physical change, but when it's lit it's a chemical change.
This is a physical change. It's a little trickier, but if the steam is contained and cools down, it turns back to water.
The Bubbles show a physical change.