Design and Applied Technology Basics: Application and Exam Foundations
FoundationThis lesson introduces the properties of metals, plastics and wood, the factors behind choosing materials, and basic exam techniques for answering material-selection and design-cycle questions.
- Common materials fall into metals, plastics and wood, whose contrasting properties decide their typical uses.
- Metals are strong, durable and conductive; plastics are light, waterproof and mouldable; wood is warm, workable but moisture-sensitive.
- Material selection balances function, cost, workability, appearance, safety and the environment, with fitness for purpose first.
文體小知識：科技知識說明文——介紹金屬、塑料、木材三大類材料的特性與選材考慮，並示範選材與設計循環題型的基礎作答方法。
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1Materials are the physical basis of design, and common materials fall into three broad groups: metals, plastics and wood. Metals are hard, strong, durable and conduct heat and electricity; aluminium alloy and stainless steel are everyday examples. Plastics are light, easily moulded and waterproof, with many types such as acrylic and polypropylene. Wood feels warm, cuts and works easily, and shows natural grain; solid wood and plywood serve different purposes.
2Because properties differ, choosing materials is a key design decision. Designers weigh strength and durability, weight, cost, appearance and texture, resistance to water and rust, and ease of working. For a school water bottle, light and impact-resistant plastics often beat dent-prone metals; for a chair frame, strong metal or hardwood is usually more suitable.
3Rapid forming technology makes materials more flexible to use. 3D printing builds an object layer by layer from a computer model and can produce complex shapes that traditional crafts find difficult, which suits prototypes and small batches. It is, however, usually slower and costlier, so mass production still relies on methods such as injection moulding; designers choose the process according to quantity and requirements.
4For assessments, material questions and design-cycle questions have basic answering patterns. For materials, remember to match properties to purposes: state the property first, then explain how it meets the product's requirements. For design-cycle questions, answer in the order of identifying needs, specification, idea generation, prototyping, testing and evaluation, tying every stage to the situation given. Structured, well-matched answers earn marks steadily.
1Summary 重點摘要
This lesson introduces the properties of metals, plastics and wood, the factors behind choosing materials, and basic exam techniques for answering material-selection and design-cycle questions.
2Vocabulary cards Vocabulary
Hard, strong materials that conduct heat and electricity, such as aluminium alloy and stainless steel.
Light, easily moulded, waterproof polymer materials such as acrylic.
Warm, easily worked materials with natural grain; solid wood and plywood have different uses.
Choosing suitable materials by weighing properties, cost and workability against product requirements.
The ability of a material to resist forces without breaking.
The quality of resisting wear, deformation or rust over long use.
Shaping materials into required forms by cutting, sanding, joining and similar methods.
A rapid forming technology that builds objects layer by layer from a computer model.
A mass-production process that injects molten plastic into a mould and cools it into shape.
3Step by step Steps
- Step 1: Recognising the three common material groupsCommon materials fall into three groups, each with a distinct character. Metals are hard, strong, durable and conduct heat and electricity, but they are heavier and can rust. Plastics are light, waterproof and easily moulded into complex shapes, yet they deform under heat and degrade slowly. Wood is warm, attractive and easy to cut and join, but it fears moisture and insects, and its strength depends on grain direction. For example, kitchenware uses stainless steel, bottles use plastics and furniture uses wood — properties decide.
- Step 2: Properties and uses of metalsThe great strengths of metals are strength and durability: they bear impact and heavy loads, conduct heat and electricity, and can be welded, bent and polished. Aluminium alloy is light and rust-resistant, used in window frames and electronics casings; stainless steel resists rust and wear, used in kitchenware and medical instruments. For example, bicycle frames are usually aluminium alloy because they must carry the rider's weight while keeping the whole bike light — metal strength and weldability meet both demands at once.
- Step 3: Properties and uses of plasticsPlastics are light, waterproof and insulating; when heated they can be moulded into complex shapes, they come in many colours and are generally cheap, making them the mainstay of product casings and daily goods. Different plastics differ in character: acrylic is as clear as glass but lighter and safer, while polypropylene is tough and fold-resistant, ideal for living hinges. For example, the flexible lid of a ring binder must survive years of repeated openings, so fold-resistant polypropylene is chosen; a brittle plastic would crack quickly.
- Step 4: Properties and uses of woodWood is warm with natural grain, easy to saw, sand and join. Plywood bonds thin sheets layer upon layer, giving even strength while saving material, and is common in furniture and models. Wood is stronger along the grain than across it, and it swells or shrinks with moisture, which designers must note. For example, bookshelf panels use plywood or solid wood for their good bending strength along the grain, while bathroom furniture needs moisture-treated board to avoid warping and mould.
- Step 5: Factors in choosing materialsChoosing materials is a many-sided balance: first the functional demands of strength, weight, water resistance and durability; then cost and ease of working, since expensive or hard-to-work materials raise the price; finally appearance, safety and environmental impact. Take a schoolbag buckle as an example: plastic is light, rust-free and mouldable into a hand-friendly curve, and cheaper than metal, so it fits best; apply the same logic to a bicycle brake lever and metal wins.
- Step 6: Exam foundations — answering material and cycle questionsFor material questions, remember the three steps of matching properties to purposes: name the material and its properties, state the product's requirements, then explain how the properties meet them — never give a bare conclusion. For design-cycle questions, organise paragraphs in the order of identifying needs, research and specification, idea generation, prototyping, testing and evaluation, tying each stage to the given situation. Take designing a signpost for country parks as an example: answer with weatherproof materials, clear height and lettering, then unfold the cycle stage by stage.
5Worked example Example
Worked example: The school wants a row of lockers in an open corridor for students to store sports gear. Suggest a suitable material for the locker bodies and justify your choice.
- List the product requirements: outdoor use demands moisture and sun resistance, durability, safety without sharp edges, plus reasonable cost and appearance.
- Compare candidate materials: metal is strong but conducts heat and needs anti-rust treatment; solid wood is attractive but fears moisture; plastic is waterproof, durable and maintenance-free.
- Apply matching properties to purposes: a plastic body resists water and rust, is light and easily formed, meeting the outdoor and durability requirements.
- Add design details: ventilation slots, rounded corners and a raised base to avoid standing water.
- Answer: Recommend waterproof plastics such as polyethylene or ultraviolet-treated plastic board for the locker body: they resist moisture and rust, stay durable and easy to clean, can be formed in one piece and cost reasonably; rounded corners and a raised base complete the design. The key is that every property answers a requirement — never just name a material.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which group of materials is light, waterproof and easily moulded?
Q2Why is aluminium alloy commonly used for bicycle frames?
Q3Why is polypropylene often used for ring binder lids?
Q4For which tasks is 3D printing best suited?
Q5What are the basic steps for answering a material question?
8Recap Recap
- Common materials fall into metals, plastics and wood, whose contrasting properties decide their typical uses.
- Metals are strong, durable and conductive; plastics are light, waterproof and mouldable; wood is warm, workable but moisture-sensitive.
- Material selection balances function, cost, workability, appearance, safety and the environment, with fitness for purpose first.
- 3D printing forms objects layer by layer, suiting prototypes and small batches; mass production favours mould processes such as injection moulding.
- Answer material questions in three steps of matching properties to purposes; answer design-cycle questions stage by stage, tied to the context.