Planning and running an independent ESS investigation

What AS 91410 asks of you

• AS 91410 is a 4-credit internal: you choose your own Earth and Space Science question, plan and run the investigation yourself, and write a report.
• Achieved needs a clear purpose, a method that names the range of the independent variable, how you measure the dependent variable, how you control other variables and limit error and bias, then raw data, processed data, a conclusion and the science behind it.
• Merit needs a method you have trialled and then confirmed or improved, a conclusion the data really support, and an in-depth explanation of both the science and why your data are valid and reliable.
• Excellence needs you to justify every key method choice and to evaluate the whole investigation against the relevant Earth and Space Science: what fits, what does not, and why.
• Independent means the question and the method come from you; your teacher can suggest a broad area, but not hand you the plan.

Choosing a question you can actually answer

• Start from something in Earth or space that interests you, then narrow it until there is one thing you change or select (the independent variable) and one thing you measure (the dependent variable).
• Primary data are measurements you make yourself, in the lab or the field; secondary data are measurements someone else made, such as NIWA's CliFlo climate records or GeoNet's earthquake catalogue.
• Most schools expect the core of 91410 to be your own practical data; a secondary dataset you process yourself can work too if your school's conditions allow it, and it is always useful for comparing with your own results.
• Aroha's interest was the seasons. Her purpose: to find how the angle at which light strikes a surface affects how much that surface warms in 10 minutes, as a model of the Sun at different heights in the sky.
• Her hypothesis gave a reason: at a lower angle the same beam is spread over a larger area, so each square centimetre receives less energy and warms less.

Aroha's method

• Independent variable: the angle between the lamp's beam and the card, at 15°, 30°, 45°, 60°, 75° and 90°, set with a protractor. Six values spread over the whole possible range show the shape of the relationship, not just its direction.
• Dependent variable: the rise in temperature of a black card after exactly 10 minutes, read from a thermometer taped under the card so the bulb is not lit directly.
• Controlled variables: the same 60 W incandescent lamp, always 30 cm from the centre of the card measured along the beam with a piece of string, the same card, a room with no draughts, and the card starting at room temperature every run.
• Three runs at each angle, in a random order, so any slow drift in room temperature does not line up with the angle.

The trial run that improved the method

• Aroha did a short trial before collecting her real data, and it changed three things; describing these changes is what Merit reports do.
• Problem: with the thermometer bulb on top of the card, the lamp heated the glass bulb directly, so readings were too high. Fix: tape the bulb underneath, so it measures the card.
• Problem: the distance from lamp to card changed as she tilted the lamp. Fix: a 30 cm string from lamp to card centre, pulled tight for every angle.
• Problem: the card was still warm from one run when the next started. Fix: two identical cards used in turn, each checked to be back at room temperature before a run.
• Each fix improved validity (the readings now measure the warming of the card caused by the angle alone), while the three repeats improved reliability.

Try it: fit a line to processed data

Linking the results to the Earth and Space Science

• A beam of cross-section A hitting a surface at angle θ spreads over an area A ÷ sin θ, so the energy arriving per square metre is multiplied by sin θ.
• The Sun's height above the horizon at noon plays the same part as Aroha's lamp angle: at an equinox it is 90° minus your latitude, and the 23.4° tilt of Earth's axis adds or takes away up to 23.4° through the year.
• That is why the tropics, with the Sun high all year, receive far more energy per square metre than the poles, and why New Zealand's summer noon Sun heats the ground so much more than its winter one.
• Day length adds to the effect in summer, and a low Sun's light also passes through more atmosphere, so real seasons are stronger than the angle alone predicts.

Sky and seasons

Evaluating the investigation

• Reliability: the repeats at each angle were within 0.3 °C of each other, and the means sat close to the line, so another run of the method would very likely give the same pattern.
• Validity: the trial fixes meant the thermometer measured the card, not the lamp, at a fixed distance, so the change in rise was caused by the angle.
• Limitations: a lamp's light spreads out from a point while sunlight arrives as parallel rays, so at low angles the far edge of the card was further from the lamp; the thermometer read to 0.1 °C, so the smallest rises have the largest percentage error.
• Against the science: the lab model tests the angle effect only; it leaves out day length and the longer path through the atmosphere, which strengthen real seasons, and Excellence reports say so.

What Achieved, Merit and Excellence look like

• The same result, written up at each grade. Notice that Excellence justifies a choice and evaluates against the science rather than just describing.