Newton's Second Law
Topic 2.4 named the no-net-force case: the velocity stays put. Newton's second law names what happens when the net force isn't zero. The center of mass accelerates, in the direction of the net force, with size $|\vec F_\text{net}|/m$. That is the whole law. The rest is reading it carefully.
Three traps lurk inside that one sentence. The first is reaching for $F = ma$ as a formula before the $F$ on the left is built up as the net external force on the system. The second is letting the velocity decide the direction of the acceleration, when only the net force gets a vote. The third is quoting $F_N = mg$ as a rule of physics rather than an equation that happens to hold on level ground. The lesson walks through all three.
The work
3 ways in · any order
Lesson
Newton's Second Law
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Read the lesson. Three worked examples (frictionless ramp, accelerating elevator, Atwood machine) followed by a ten-scenario applet that drills every way the second law gets misread.
Diagnostic
10-item topic check
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Ten multiple-choice items diagnose which Newton's-second-law misconceptions you carry into the topic. Results map to the three pitfalls and to the remediation drills.
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.