Fig. 12 shows a section of timber with visible defects. The timber has been selected for its working properties and appearance. Different types of timber ha...

(a) Naming the timber defects:

• G: Knot. [1] A knot is a section of the timber where a branch originally grew from the trunk of the tree. It appears as a dark, hard oval or circular area with grain running at a different angle to the surrounding wood. The branch wood is denser and harder than the main trunk timber.
• H: Shakes (also called splits or checks). [1] These are cracks that run along or across the grain of the timber. Shakes can develop during the growth of the tree (due to wind stress or frost) or during the seasoning process when uneven drying causes internal stresses that split the wood.
• J: Warping (bowing or cupping). [1] Warping occurs when the timber bends or curves away from a flat plane. The dashed line in the diagram shows the timber deviating from straight, indicating that it has distorted. Warping is typically caused by uneven drying, differences in grain density, or the way the board was cut from the log.

(b) One way in which the defect labelled G (a knot) could affect the strength of the timber:

A knot creates a weak point in the timber because the grain direction changes abruptly around it. [1] The normal straight grain of the surrounding wood is disrupted and diverted by the knot, reducing the timber's ability to resist bending or tensile forces at that location. The timber is more likely to split or fracture at the knot, particularly under load. Additionally, knots can shrink and fall out over time, leaving a hole that further weakens the cross-section.