GED and HiSET science — physical science

Physical science on these tests means chemistry and physics at the level where the reasoning matters more than the algebra. There is no notation anywhere in this set — substances are named in words, every number is a plain digit with its unit written out, and each question can be worked through on paper or read aloud.

Two of the twelve are worth describing, because they are the ones people get wrong for interesting reasons.

Ten grams of dry wood burn in an open dish and leave two grams of ash. Where did the other eight go? Up as carbon dioxide and water vapor, which is the expected answer — but the explanation goes one step further, because the step is the point: those gases weigh more than eight grams, since oxygen from the air combined with the wood and left with it. A fire looks like destruction and is a rearrangement, with the air as an ingredient.

An atom of carbon gains one proton. What is it now? It is nitrogen, because protons decide the element — and the question deliberately adds an electron alongside the proton, since a proton by itself would leave a nitrogen ion rather than a nitrogen atom. Three particles do three different jobs: protons fix the element, neutrons fix the isotope, electrons fix the charge. That distinction is the thing being tested, and blurring it is the usual way such questions are set.

The rest is the standard ground, asked from a situation rather than a definition: dissolving sugar against a reaction that fizzes; ice that absorbs heat at a steady zero degrees, because the energy is going into separating molecules rather than speeding them up; a pH of 12 and what it implies; a cyclist's average speed from sixty kilometers in three hours; a skateboarder pushing off a wall; a crate that stops because friction acts against it; a hair dryer traced from the socket outward, where one input splits into heat in the coil and motion in the fan; a hundred joules at the top of a fall and the same hundred at the bottom; warmth felt across the air from a campfire; and two strings of lights, one in series and one in parallel, with a bulb burnt out in each.

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• Tell a physical change from a chemical one when both look similar
• Account for mass that appears to vanish in a fire, including where the extra weight of the gases comes from
• Explain why temperature holds steady while ice melts
• Say what protons, neutrons and electrons each determine about an atom
• Read the pH scale and calculate an average speed from a distance and a time
• Identify Newton's third law in a scene, and explain why a moving crate stops
• Trace an energy chain through one device, and apply conservation of energy to a fall
• Name the kind of heat transfer at work in a described case, and predict how series and parallel circuits fail

Written for this exercise; substances are named in words and all figures are plain digits. From the bank: "A 10-gram piece of dry wood is burned in an open dish. When the fire goes out, the ash left in the dish weighs 2 grams. What became of the other 8 grams?" The answer is the gases that left with the smoke — which, as the explanation notes, weigh more than 8 grams, because oxygen from the air went with them.