What is a physical change?
A change in (matter or substance) which does not alter the chemical properties of the matter.
A physical change is a type of change in which the form of matter (substance) is altered but one substance is not transformed into another different substance. For example, if we carve a piece of wood into a baseball bat, it will still burn in a fire and float on water. It remains wood, so it is a physical change.
(b) Crushing a can : after crushing can changes its shape, size but it still remain Aluminum so it is a physical change.
Burning of wood is a chemical change because on burning wood changes to a totally different new products (ash, smoke and carbon dioxide).
Here is video of a lab with a number of examples of both chemical and physical changes.
video from: Noel Pauller
Simple explanation with good results can be on this site http://chemistry.about.com/od/matter/a/10-Physical-Change-Examples.htm