AP Physics C: Mechanics · Unit 0: Calculus Primer ·  Lesson 0.5

Definite Integrals and Area Under a Curve

The single geometric picture behind half of this course's equations  ·  Approx. 1–2 class days

Starring∫ₐᵇ f(x) dx = F(b) − F(a)Δx = ∫[t₁,t₂] v(t) dt

Use this as a quick reference for the Fundamental Theorem of Calculus, Riemann sums, and the "area under the curve" pattern that shows up across the whole course.

Definite Integrals and Area Under a Curve infographic

🧭 Plot Summary

Lesson 0.4 found families of antiderivatives, each one still missing a specific constant. This lesson closes that gap by asking a slightly different question: what if you evaluate an antiderivative at two specific points and subtract? That small change turns integration into something concrete — a single number — and that number has a beautiful geometric meaning: it's the area between a curve and the x-axis. This one idea, area under a curve, is the picture hiding behind an enormous number of physics equations you'll meet this year.

What you'll do in this lesson

  • State and apply the Fundamental Theorem of Calculus.
  • See why the constant of integration disappears in a definite integral.
  • Interpret a definite integral geometrically as signed area under a curve.
  • Watch a Riemann sum converge to an exact area as rectangles get thinner.
  • Check a definite integral's value against a geometric area calculation.
  • Compute displacement, work, and impulse — all as area under a curve.

Why it matters

Δx = ∫v dt, W = ∫F dx, and J = ∫F dt look like three unrelated formulas from three different units. They're the same idea, three times: displacement is the area under a velocity-time graph, work is the area under a force-position graph, and impulse is the area under a force-time graph.

Self-Check Before You Roll On

Check off each item as you get there. These aren't grades — they're your own signal.