Why Does Lumber Shrink When It Dries?

When lumber dries, it tends to shrink:

Lumber shrinks as it dries due to evaporation of moisture content, leading to the contraction of wood fibers. This is an example of physical changes resulting from thermal stress.

Explanation:

The correct answer is option Physics. Lumber, or processed wood from the sawmill, tends to shrink as it dries because of the loss of moisture content. In its natural state, wood contains a significant amount of water which is held in the wood fibers.

When the lumber is cut and removed from its source of moisture, it begins to lose this water content through the process of evaporation. As the wood fibers lose moisture, they contract, causing the lumber to shrink.

Such shrinkage is an example of physical changes due to thermal stress and the response of materials to changes in temperature and moisture content.

The phenomena of expansion and contraction due to temperature and moisture changes are not just limited to lumber but can be observed in various materials, including metals, concrete, and even biological cells.

Shrinkage can affect not only the size of the lumber but also its shape, potentially leading to warping or twisting if the drying is uneven. Thus, understanding this process is critical in industries that rely on wood products, to minimize structural issues and ensure the quality and integrity of the end product.

Do all types of wood shrink when they dry?

Yes, all types of wood tend to shrink when they dry. The degree of shrinkage may vary depending on the species of wood and the conditions under which it dries, but the basic principle of moisture loss leading to the contraction of wood fibers applies to all types of wood.