Net force is the vector sum of every individual force acting on an object, and by Newton's second law (F_net = ma) it determines the object's acceleration. Zero net force means constant velocity, not necessarily rest. In AP Physics 2 it shows up with buoyant, electric, and magnetic forces.
Net force is what you get when you add up every force acting on an object as vectors, keeping track of both size and direction. Two forces of 10 N pointing opposite ways give a net force of zero. Two forces of 10 N pointing the same way give 20 N. Newton's second law, F_net = ma, then tells you exactly how the object responds. A nonzero net force means the object accelerates in the direction of that net force.
Here's the part that matters for AP Physics 2: net force is not a new force you draw on a free-body diagram. It's the result of combining the real forces, things like gravity, tension, buoyancy, electric force, and magnetic force. Think of the free-body diagram as the ingredients list and net force as the finished dish. Physics 2 takes the same Newton's-laws machinery from Physics 1 and feeds it new ingredients, like the buoyant force on a submerged block or the electric force pulling an electron toward a proton.
Net force is the connective tissue of AP Physics 2. The course doesn't have a unit called "net force," because the idea runs underneath almost every unit instead. When you analyze a charge sitting still between two charged plates (Unit 10), a current-carrying wire in a magnetic field (Unit 12), or an object hanging from a string while submerged in a fluid, the question is always the same. What are all the forces, what do they add up to, and what does F_net = ma say happens next? AP Physics 2 assumes you already mastered this from Physics 1, then tests whether you can apply it to unfamiliar forces. If you can write a correct net-force equation, you can usually unlock the rest of the problem, including derivations and equilibrium arguments that show up constantly in free-response questions.
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Buoyancy and Archimedes' Principle (Physics 1, Unit 8 crossover)
The buoyant force is just one more arrow in the net-force sum. A floating object floats because buoyancy up equals gravity down, so the net force is zero. The 2022 SAQ Q1 setup, a block held underwater by a string, is pure net-force bookkeeping with tension, gravity, and buoyancy.
Electric Force, Field, and Potential (Unit 10)
Coulomb forces from multiple charges combine as vectors into one net force, which then sets the charge's acceleration. The 2022 LEQ on the hydrogen atom hinges on recognizing that the electric force on the electron IS the net force, and it points toward the center of the circular orbit.
Magnetic Force on Moving Charges (Unit 12)
When a charged particle moves through a magnetic field, the magnetic force qvB often acts as the net force keeping it in a circle. Setting qvB equal to mv²/r is one of the most reused moves in the whole course.
Tension and Normal Force (used across every unit)
Tension and normal forces are contact forces that show up in nearly every lab-style setup. They're the adjustable pieces of the net-force equation. A string or surface supplies exactly the force needed to balance everything else when the object isn't accelerating.
You almost never see a question that just asks "what is net force?" Instead, the exam hands you a situation and expects you to build the net-force equation yourself. On the 2022 exam, a short-answer question had a block of density ρ_b suspended by a string in a fluid, and the productive first step was summing tension, gravity, and buoyancy to zero. The same year's long FRQ modeled a hydrogen atom as an electron in a circular orbit, where you had to recognize the electric force as the net force and set it equal to mv²/r to derive the electron's speed. Multiple-choice stems do the same thing in miniature, asking for the direction of acceleration, whether an object is in equilibrium, or which free-body diagram is correct. Your jobs are always the same. Draw the free-body diagram with individual forces only, write F_net = ma along a chosen direction, and solve or argue from there. Graders award points for the correct net-force equation even if the algebra goes sideways later.
Tension, normal force, gravity, and buoyancy are real, individual pushes and pulls with identifiable sources. Net force is not one of them. It's the vector total of all of them. That's why drawing a "net force arrow" on a free-body diagram costs you points. The diagram shows ingredients; net force is the result you calculate from them.
Net force is the vector sum of all individual forces on an object, so direction matters just as much as magnitude.
Newton's second law, F_net = ma, means the net force and the acceleration always point in the same direction.
Zero net force means constant velocity, which includes both an object at rest and an object cruising at steady speed in a straight line.
For circular motion, like an electron orbiting a proton, the net force points toward the center and equals mv²/r.
Never draw a net force arrow on a free-body diagram; only draw the individual forces, then add them to find the net force.
In AP Physics 2, the new forces (buoyant, electric, magnetic) plug into the exact same net-force framework you learned in Physics 1.
Net force is the vector sum of every force acting on an object, and through F_net = ma it determines the object's acceleration. In AP Physics 2 those forces include buoyancy, electric force, and magnetic force, not just gravity and tension.
No. Zero net force means zero acceleration, so the object keeps doing whatever it was doing. It could be at rest, or it could be moving at a constant velocity, like a block floating in equilibrium or a charge drifting at steady speed.
No. Gravity and tension are individual forces with specific sources, while net force is the total you get after adding all of them as vectors. On the 2022 exam's submerged-block question, the net force was the combination of tension, gravity, and buoyancy, and it equaled zero.
No, and AP graders specifically dock free-body diagrams that include a net force arrow. Draw only the individual forces acting on the object, then calculate the net force from those arrows.
Break each force into components along your chosen axes, add the components in each direction (with signs), and combine the results into a single vector. For circular motion problems, like the 2022 hydrogen atom FRQ, point one axis toward the center and set the net force equal to mv²/r.