AP Physics C · Unit 2
Newton's Laws of Motion: every key term you need (+ practice quiz)
21 flashcard terms for AP Physics C Unit 2, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 10-question quiz — free, no account needed.
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Newton's First Law An object at rest stays at rest and one in motion stays in constant-velocity motion unless a net external force acts (inertia).
Newton's Second Law F_net = ma, more generally F = dp/dt; net force equals rate of change of momentum; a vector equation applied per axis.
Newton's Third Law Forces come in equal-and-opposite pairs on different bodies: F_AB = −F_BA; the two forces never act on the same object.
Free-Body Diagram A sketch of a single object with every external force drawn as a vector from it; the basis for applying ΣF = ma.
Weight W = mg; the gravitational force on a mass; a downward force distinct from mass, which is the amount of matter.
Normal Force N; the contact force perpendicular to a surface; adjusts to prevent interpenetration and is not always equal to mg.
Tension Force transmitted along a string or rope; for an ideal massless rope over an ideal pulley the tension is the same throughout.
Static Friction f_s ≤ μ_s N; opposes impending motion up to a maximum; adjusts to match applied force until slipping begins.
Kinetic Friction f_k = μ_k N; opposes sliding motion with roughly constant magnitude; usually μ_k < μ_s.
Inclined Plane Components Resolve weight along the incline (mg sinθ) and perpendicular to it (mg cosθ); the normal force balances mg cosθ.
Block on a Frictionless Incline Acceleration down the slope is a = g sinθ, independent of mass; the net force is mg sinθ along the incline.
Normal Force on an Incline N = mg cosθ for a block resting on a slope of angle θ; smaller than the weight for θ > 0.
Connected Bodies Treat linked masses as a system for acceleration, then isolate one body to find the internal tension via its own free-body diagram.
Atwood Machine Two masses over a pulley: a = (m₂ − m₁)g/(m₁ + m₂); tension T = 2m₁m₂g/(m₁ + m₂) for an ideal setup.
Resistive (Drag) Force A velocity-dependent retarding force; common models are F = −bv (linear) or F = −cv² (quadratic) opposing motion.
Equation of Motion with Linear Drag m dv/dt = mg − bv for a falling body; a first-order ODE whose solution approaches a constant speed.
Terminal Velocity The speed at which drag balances weight so net force and acceleration are zero; v_t = mg/b (linear) or √(mg/c) (quadratic).
Velocity vs Time with Drag v(t) = v_t(1 − e^(−bt/m)) for a body released from rest with linear drag; approaches v_t exponentially.
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Equilibrium When F_net = 0 the object has zero acceleration: it is at rest or moving at constant velocity (dynamic equilibrium).
Apparent Weight The normal force felt in an accelerating frame, e.g. N = m(g + a) in an upward-accelerating elevator; differs from true weight mg.
Mass vs Weight Mass (kg) is an intrinsic scalar measuring inertia; weight (N) is the gravitational force mg and varies with local g.
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