A physical change is when the physical properties of an object change, whereas a chemical change is when the chemical properties of an object change. Iron rusting is a result of a chemical change, because the rust was not there before. Silver tarnishing is a chemical change for the same reason. Gasoline burning is also a chemical change, because gasoline changes chemically. Therefore, metal denting is a physical change, because the shape and position of an object is a physical property, and there are no new substances being formed, which are all indications of a physical change.