TASC Physical Sciences Level 3 common mistakes
TASC Physical Sciences Level 3 · Understand the traps and how to avoid them.
When asked to identify a testable hypothesis or a controlled variable in a described investigation, the candidate picks the statement that merely restates the observation or proposes an untestable opinion, and fails to specify which variable the experimenter deliberately changes.
Candidates conflate a hypothesis with a prediction or a summary of the data, and they have not practised separating independent, dependent, and controlled variables from a prose description of a procedure.
What to do instead
For every investigation prompt, write three labels before answering: what the experimenter changes (independent), what is measured (dependent), and what is held constant (controlled). A hypothesis must name a relationship between the first two. Eliminate any option that cannot be falsified by measurement.
The candidate reads a data table or simple graph and reports the single highest value as the trend, ignoring the direction of change across the whole range or the units on each axis.
Graph and table interpretation is often skimmed under time pressure; candidates look for one familiar number instead of describing how the dependent variable responds as the independent variable increases.
What to do instead
Before selecting an answer, state the trend in one sentence using the axis labels and units ('as X increases from 2 to 8, Y doubles'). Check whether the relationship is linear, inverse, or flat, and reject options that describe only one data point.
The candidate computes average speed by dividing total distance by the final time reading rather than total elapsed time, or adds velocities directly when a direction change is involved.
Everyday language treats 'speed' and 'how far in how long' loosely, and candidates forget that average speed uses the whole time interval while velocity is a vector that can cancel across a round trip.
What to do instead
Write the formula first: average speed = total distance / total time, and average velocity = displacement / total time. For any trip that returns to the start, mark displacement as zero before computing. Keep units attached throughout so a mismatch (minutes versus hours) is visible.
The candidate treats Newton's third-law pairs as balanced forces acting on the same object, concluding that a book on a table cannot accelerate because the forces 'cancel'.
Action-reaction pairs feel like balancing forces, and candidates do not track which object each force acts on; free-body diagrams are rarely drawn in the exam setting.
What to do instead
For each force problem, draw a box for the object of interest and draw only forces acting on that box. Then check: do the remaining forces sum to zero? If not, the object accelerates in the direction of the net force. Action-reaction pairs always act on two different objects and never appear on the same diagram.
The candidate assumes energy is 'used up' or lost as heat when a ball rolls down a ramp, and therefore predicts a lower final speed than conservation of energy allows, or claims mechanical energy is always conserved.
The word 'energy' in ordinary speech implies consumption, and candidates do not distinguish conservative forces (gravity) from non-conservative ones (friction).
What to do instead
Set up the accounting explicitly: initial potential plus kinetic energy equals final potential plus kinetic energy plus energy dissipated by friction. State whether friction is negligible. If it is, mechanical energy is conserved and speed depends only on height change, not on the path or mass.
When predicting products of a simple reaction, the candidate balances the equation by changing subscripts in a formula (writing H2O2 as H2O to make atoms match) rather than adjusting coefficients.
Balancing feels like an arithmetic puzzle, and altering a subscript appears to fix the count quickly; candidates have not internalised that subscripts define the substance's identity.
What to do instead
Balance only with coefficients in front of formulas. Count each element on both sides in a table, adjust one coefficient at a time, and re-check every element after each change. If a subscript change seems necessary, the product formula itself is probably wrong and should be reconsidered.
The candidate classifies a substance as a compound, mixture, or element based on its name or appearance rather than on whether it can be separated by physical means or has a fixed composition.
Names like 'salt water' and 'table salt' sound similar, and candidates rely on familiarity with everyday materials instead of applying the operational definitions of element, compound, and mixture.
What to do instead
Apply a decision sequence: can it be broken down by physical methods such as filtration or evaporation? If yes, it is a mixture. If only chemical means separate it into elements in fixed proportions, it is a compound. If no method separates it, it is an element. Check for a fixed mass ratio to confirm compound status.
The candidate counts electrons in the outermost shell incorrectly for an element in period 3 or beyond, or places electrons in the wrong shell when writing an electron configuration, leading to the wrong group or bonding prediction.
Candidates memorise the first few elements but do not apply the shell-filling pattern (2, 8, 8) to unfamiliar atomic numbers, and confuse group number with period number.
What to do instead
Write the atomic number, fill shells in order (2, then 8, then 8) until electrons run out, and read the outermost count to find the group. The number of filled shells gives the period. Use the outer count to predict whether the atom tends to lose, gain, or share electrons.
The candidate explains seasons by the Earth's changing distance from the Sun, or explains day and night by the Earth's orbit, rather than by axial tilt and rotation.
Diagrams showing an elliptical orbit exaggerate the distance variation, and the tilt-rotation distinction is easily swapped because both involve the Earth's motion.
What to do instead
Anchor two facts: day and night come from rotation on the axis every 24 hours; seasons come from the fixed 23.5-degree tilt changing the angle and duration of sunlight at each latitude. Note that distance variation is small and would produce two summers per year, contradicting observation.
The candidate applies a physics or chemistry concept to an Earth or environmental scenario without matching the scale or units, for example treating a local temperature rise as proof of a global trend or ignoring that energy figures for a region are per unit area.
Interdisciplinary items mix familiar vocabulary with unfamiliar contexts, and candidates transfer a rule by keyword association rather than checking what the quantities actually measure.
What to do instead
Restate the scenario in the question's own units before choosing: identify the region, the time span, and whether the quantity is a total or a rate per area. Ask whether the evidence supports a local claim, a global claim, or neither, and eliminate options that overgeneralise from one measurement.