Humidity and its effect on various species of wood
The hypothesis that humidity may cause different types of wood to expand and shrink at different rates, is proven to be correct.
It is much easier to work with a dry piece of wood than a freshly cut piece of wood. When moisture has been removed from the wood, it is lighter and easier to work with and handle. Kiln-dried wood is also easier and more cost effective to handle, store and ship to other places or countries. Dried wood is also easier to cut. Furthermore, the wood strengthens as it dries.
Try using more than 1 piece of each type of wood for the experiment, for more accurate results.
Try this science fair project with other types of woods such as birch, fir, pine or hemlock.
Try exposing the wood to different levels of humidity in a humidity chamber and compare the rate of expansion for each type of wood.
Wood movement - http://www.woodworkerssource.com/wood_movement.php
Allowing for expansion and shrinking - http://woodworking.about.com/od/dealingwithproblems/p/expansion.htm
The oven should not be left unattended when the pieces of wood are left to dry in the oven for 24 hours. There is a possibility of the wood catching fire (although it is unlikely, if a proper temperature setting is used). Have fire safety equipment on standby. Be careful when removing the hot wooden blocks from the oven. Use gloves for protection.