Scientific words gain precision from the context in which they are used. These definitions are starting points for reading and conversation. When a paper gives a more specific definition, keep that definition with your notes. The same familiar word may carry a narrower technical meaning in a particular field.
Observation
An observation is a record made by attending to something in the world, directly or through an instrument. It might be a colour description, a microscope image, or a temperature reading. Record how, where, and when it was obtained. “A dark line appears in the image” describes an observation; “the material has cracked” adds an interpretation that may require another view or measurement.
Model
A model represents selected features of something so that we can describe, explore, or predict its behaviour. It may be a diagram, a physical object, a set of equations, or computer code. A map is useful because it leaves things out. Likewise, ask what a scientific model includes, what it simplifies, and which question it was built to address before relying on its predictions.
Evidence
Evidence is information used to assess a claim or explanation. A measurement becomes relevant evidence through a reasoned connection to the question being asked. A photograph of a bent strip may support a description of its shape, but it does not by itself establish what caused the bending. Ask how the record was produced, what alternatives it distinguishes, and what remains unresolved.
Uncertainty
Uncertainty describes limits to what is known. In measurement, it has a specific quantitative meaning: a characterization of the spread of values reasonably attributable to the quantity being measured, based on the available information. It is not simply a synonym for a mistake. A reported value becomes more informative when its uncertainty, units, and method are stated together. Check how an author defines a displayed interval.
System
A system is a set of interacting parts considered together. Its boundary is a choice that should suit the question. Studying a room's temperature might involve the air, walls, windows, and heating system, with energy crossing the boundary. Begin by naming the parts and their relationships. Then ask which inputs, outputs, or outside influences the chosen boundary leaves you responsible for tracking.
Scale
Scale concerns the size, duration, or range at which something is described or observed. A surface may look smooth to the eye and uneven through a microscope. An hourly record and an annual average can reveal different features of the same process. Always ask about spatial resolution, time interval, and units. Moving to another scale can require different observations and a different explanation.
Use the words together
Try describing a familiar scene, such as sunlight entering a room. Identify the system you want to discuss and the scale of your observation. Separate what you recorded from a model of what might be happening. State the claim for which the record could serve as evidence, and name an uncertainty that would affect the interpretation.
The purpose is a clearer account, not a longer vocabulary. If a term hides an assumption, replace it with a concrete description and ask what additional information would make that description more useful.
Further reading
- Systems and system models — My NASA Data
- Measurement uncertainty — National Institute of Standards and Technology
- Scale, proportion, and quantity — My NASA Data
A good question has somewhere to go.
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