This trips up almost every Physics 1 student at some point. On a flat surface with no acceleration: yes, normal force equals mg. But the moment you add an incline, acceleration, or an extra applied force, that changes everything. Normal force is whatever it needs to be to keep the object from passing through the surface. You calculate it, you don't assume it. Test yourself: a 10.0 kg box sits on a scale in an elevator accelerating upward at 2.00 m/s². What does the scale read? Reply below with your answer and your reasoning.

The net work done on an object equals the change in its kinetic energy. That's it. That's the whole theorem. What this means practically: if something speeds up, net work was done ON it. If it slows down, net work was done AGAINST it. If it moves at constant speed, net work is zero. Here's where students get tripped up, they confuse work done by one force with NET work done by all forces combined. Always ask: what is the NET work? Not just the work done by one force. Quick check: a car brakes to a stop. Is the net work positive, negative, or zero? Reply below.

Students hear "every action has an equal and opposite reaction" and think the two forces cancel out. They don't. Here's why. Action-reaction pairs act on DIFFERENT objects. The force the floor exerts on you and the force you exert on the floor are equal and opposite, but they act on different objects so they never cancel. Forces only cancel when they act on the SAME object in opposite directions. Test yourself: you're sitting in a chair right now. Name the action-reaction pair involved. Reply below — let's see who gets it right.

Is energy conserved in this problem? If yes, use conservation of energy. Simple. If no, something is adding or removing energy. Find it first. That's your work term. Most students jump straight to equations without answering this question. That's why they get stuck halfway through. One question. Asked first. Every time. That's the habit.

Most students memorize F=ma and think they're done. That's not enough. Here's the process that actually works: Step 1 — Identify every object in the problem. Step 2 — Draw a free body diagram for each one. Step 3 — Choose a coordinate system and stick to it. Step 4 — Write F=ma for each direction separately. Skip any of these steps and your answer will be wrong, even if your math is perfect. Which step do you usually skip? Reply below.