Fig. 12 shows a cross-section of a piece of plywood. The timber has been selected for its working properties and appearance. Different types of timber have ...
Question 1 Report
Fig. 12 shows a cross-section of a piece of plywood. The timber has been selected for its working properties and appearance. Different types of timber have different characteristics that affect their suitability. The grain direction and moisture content affect how the timber can be worked.
The base is wide. The sides are smooth. It works in rain and sun. The parts fit well. The grip stops it from slipping.
The surface of the PVC can be improved by applying a varnish. The product is intended for use in a school workshop environment.
(a) State why plywood is classified as a composite material. [1]
(b) Explain why the grain direction of each layer alternates. [1]
Answer Details
(a) Plywood is classified as a composite material because it is made from two or more materials bonded together to create improved properties [1]. Specifically, it consists of thin layers (veneers) of wood glued together with adhesive. The wood veneers and the adhesive are different materials that, when combined, produce a board with greater strength, stability, and resistance to splitting than a single piece of solid timber of the same thickness.
(b) The grain direction of each layer alternates (each veneer is laid at 90 degrees to the one above and below it) so that the plywood has equal strength in both directions [1]. In solid timber, the wood is strong along the grain but weak and prone to splitting across it. By alternating the grain, each layer reinforces the weakness of its neighbours. This also prevents the board from warping, twisting, or shrinking unevenly when exposed to changes in moisture, because the opposing grain directions counteract each other's tendency to move.
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