Atmosphere, resources and life-cycle decisions
| English | 中文 | Pinyin |
|---|---|---|
| life-cycle assessment/laɪf ˈsaɪkl əˈsesmənt/ | 生命周期评价 | shēng mìng zhōu qī píng jià |
| functional unit/ˈfʌŋkʃənl ˈjuːnɪt/ | 功能单位 | gōng néng dān wèi |
What would explain this observation?
- A reusable container can require more energy to manufacture than a single-use one. Its impact depends on how often it is used and what happens at disposal.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- A life-cycle assessment 生命周期评价 considers raw materials, manufacture, transport, use and end-of-life processes. Greenhouse gases absorb and emit infrared radiation; pollution and climate effects are related but distinct questions.
- life-cycle assessment: Assessment across production, use and disposal; functional unit 功能单位: The common service used for a fair comparison.
Which comparison uses a consistent functional unit?
Define the functional unit before comparing products. The same delivered service, such as carrying one litre of water a hundred times, is fairer than comparing one object with another regardless of lifetime.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Define the functional unit before comparing products. The same delivered service, such as carrying one litre of water a hundred times, is fairer than comparing one object with another regardless of lifetime.
- List system boundaries, energy sources and assumptions. Compare water demand, emissions and waste separately before making a judgement. Explain whose priorities affect the decision and where the data are uncertain.
Which two habits make the investigation or model in this case more defensible?
List system boundaries, energy sources and assumptions. Compare water demand, emissions and waste separately before making a judgement. Explain whose priorities affect the decision and where the data are uncertain.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a reusable item requires 1,000 energy units to make and 10 per use; a disposable item requires 60 per use. Equality occurs when 1,000 + 10n = 60n. Rearranging gives 1,000 = 50n, so n = 20 uses under this simplified model.
A reusable item costs 600 energy units initially and 5 per use; disposables cost 35 per use. Find break-even uses. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A reusable item costs 600 energy units initially and 5 per use; disposables cost 35 per use. Find break-even uses.
The result is 20 uses. Known: a reusable item requires 1,000 energy units to make and 10 per use; a disposable item requires 60 per use. Equality occurs when 1,000 + 10n = 60n. Rearranging gives 1,000 = 50n, so n = 20 uses under this simplified model.
Check the conclusion and its limits
- A break-even model is sensitive to cleaning, transport and disposal assumptions. Recyclable does not guarantee that an item is actually collected and recycled.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A recyclable product is always recycled after use. This claim is false: A break-even model is sensitive to cleaning, transport and disposal assumptions. Recyclable does not guarantee that an item is actually collected and recycled.
Atmosphere, resources and life-cycle decisions: Define the functional unit before comparing products. The same delivered service, such as carrying one litre of water a hundred times, is fairer than comparing one object with another regardless of lifetime.
A recyclable product is always recycled after use.
A break-even model is sensitive to cleaning, transport and disposal assumptions. Recyclable does not guarantee that an item is actually collected and recycled.
Assessment across production, use and disposal: write the technical term.
life-cycle assessment means Assessment across production, use and disposal.