Gravitational Force
Gravity is one law in two clothes. Two masses attract along the line connecting their centers, with size proportional to each mass and inverse-square in the distance: $F_g = G\dfrac{Mm}{r^2}$, pointing along the line between them. Near a planet surface, $r$ barely changes as you move around, and the law collapses to the everyday version $F_g = mg$ with $g$ pointing down at the local value of $GM/r^2$. Same physics, two zoom levels.
Three traps trip students up. Mass and weight get conflated, but mass is intrinsic (kg) and weight is the gravitational pull on that mass (N), and weight changes with location while mass does not. Doubling the distance does not halve the force; the force scales with $1/r^2$, so distance times two gives force divided by four. And $g$ is treated as a universal constant when it is really the local value of $GM/r^2$, useful near a particular surface but not a number of nature. The lesson walks all three.
The work
3 ways in · any order
Lesson
Gravitational Force
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Read the lesson. Two worked examples (weight on another planet, apparent weight in an accelerating elevator) followed by a ten-scenario applet that drills mass-versus-weight, the inverse-square scaling, and when constant-$g$ is a safe approximation.
Diagnostic
10-item topic check
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Ten multiple-choice items mapped to the gravitation failure modes: mass-weight conflation, linear-instead-of-inverse-square scaling, and treating $g$ as a universal constant. Take it cold to surface what is still shaky, or after the lesson to confirm the fix held.
Targeted Practice
Drill a single misconception
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Pick one of the failure modes you've missed and grind it on its own. The round is adaptive: two correct in a row clears the misconception and you move on.