Timber MCQ with answer and solution

Concept

Dimensional Stability of Plywood

Formula

No formula

Step-by-step solution

1. Identify that plywood is constructed from multiple thin layers (plies) of wood glued together. 2. Note that adjacent plies are arranged so their wood grains run perpendicular (at right angles) to each other. 3. Understand that alternating the grain direction counteracts wood's natural expansion and shrinkage along the grain. 4. Select Option C.

Explanation

Plywood is made by gluing thin layers (plies) of wood together so that the wood grain of each layer runs perpendicular (at right angles) to the layer next to it. Since wood expands and shrinks mainly across its grain and stays stable along its grain, placing the plies at right angles balances out the movement, making the sheet dimensions stable and reducing expansion and shrinkage.

Shortcut

A helpful shortcut to remember this is: **"Right Angles = Low Movement"** Plywood layers (plies) are glued with their wood grains running perpendicular (**at right angles**) to each other. Because wood expands across the grain but stays stable along it, alternating directions cancels out expansion and shrinkage in both directions.

Common mistake

Many students incorrectly choose option A or B, assuming that the strength of the adhesives or high-pressure gluing is what prevents expansion and shrinkage. They confuse mechanical bonding strength with dimensional stability, overlooking the fundamental structural reason that alternating grain directions (plies placed at right angles) counteracts wood's natural movement.