* Chemical change: A chemical change results in the formation of a new substance with different properties. In this case, the iron in the nail reacts with oxygen and water in the air to form iron oxide (rust). Rust has different properties than iron, like color, texture, and it is weaker and crumbly.

* Physical change: A physical change only alters the appearance or form of a substance, but not its chemical composition. Examples include melting ice or chopping wood.

Since rusting involves the creation of a new substance (iron oxide), it is a chemical change.