Arc Length by Integration Calculator
Our free statistics calculator solves arc length integration problems. Get worked examples, visual aids, and downloadable results.
Formula
L = integral from a to b of sqrt(1 + [f'(x)]^2) dx
Where L is the arc length, f'(x) is the derivative of the function, and [a, b] is the interval. The integrand sqrt(1 + [f'(x)]^2) represents the infinitesimal length element along the curve, derived from the Pythagorean theorem applied to dx and dy.
Worked Examples
Example 1: Parabola Arc Length
Problem: Find the arc length of y = x^2 from x = 0 to x = 2.
Solution: f(x) = x^2, f'(x) = 2x\nL = integral from 0 to 2 of sqrt(1 + 4x^2) dx\nUsing substitution x = (1/2)sinh(t):\nL = (1/2)[x*sqrt(1+4x^2) + (1/2)ln(2x + sqrt(1+4x^2))] from 0 to 2\nL = (1/2)[2*sqrt(17) + (1/2)ln(4 + sqrt(17))]\nL = 4.6468
Result: Arc Length = 4.6468 | Chord Length = 4.4721 | Arc/Chord Ratio = 1.0391
Example 2: Sine Wave Arc Length
Problem: Find the arc length of y = sin(x) from x = 0 to x = 2*pi.
Solution: f(x) = sin(x), f'(x) = cos(x)\nL = integral from 0 to 2*pi of sqrt(1 + cos^2(x)) dx\nThis is an elliptic integral with no closed form.\nNumerical approximation using Simpson rule with 1000 segments:\nL = 7.6404
Result: Arc Length = 7.6404 | Chord Length = 6.2832 | Arc/Chord Ratio = 1.2159
Frequently Asked Questions
What is arc length and how is it calculated using integration?
Arc length is the distance measured along a curved line or path between two points. For a function y = f(x), the arc length from x = a to x = b is calculated using the integral L = integral from a to b of sqrt(1 + [dy/dx]^2) dx. This formula comes from the Pythagorean theorem applied to infinitesimally small segments of the curve. Each tiny segment has horizontal length dx and vertical length dy, so its length is sqrt(dx^2 + dy^2) = sqrt(1 + (dy/dx)^2) dx. Summing all these infinitesimal segments via integration gives the total arc length. This fundamental calculus technique works for any smooth, continuous function.
Why is numerical integration used instead of an exact formula?
Most arc length integrals cannot be solved analytically because the square root of 1 plus the derivative squared rarely simplifies to a function with a known antiderivative. Even simple functions like y = x^2 produce arc length integrands involving sqrt(1 + 4x^2), which requires hyperbolic substitutions and produces complex expressions. For trigonometric and exponential functions, exact solutions are even rarer. Numerical methods like Simpson rule provide accurate approximations by dividing the interval into many small segments and using polynomial interpolation. With 1000 segments, Simpson rule typically achieves accuracy to six or more decimal places, which exceeds the precision needed for virtually all practical engineering and scientific applications.
What is the difference between arc length and chord length?
Chord length is the straight-line distance between two endpoints of a curve, calculated simply using the distance formula. Arc length is the actual distance measured along the curved path between those same endpoints. The arc length is always greater than or equal to the chord length, with equality only when the curve is itself a straight line. The ratio of arc length to chord length (called the arc-to-chord ratio) indicates how much the path curves. A ratio near 1 means the curve is nearly straight, while larger ratios indicate more curvature. This distinction is important in navigation, road design, cable engineering, and any application where the actual path length along a surface matters.
How does Simpson rule work for numerical integration?
Simpson rule approximates a definite integral by fitting parabolic arcs through sets of three consecutive points along the curve. The interval [a, b] is divided into an even number of subintervals of width h = (b-a)/n. The formula assigns weight 1 to the endpoints, weight 4 to odd-indexed interior points, and weight 2 to even-indexed interior points, then multiplies the weighted sum by h/3. This method is exact for polynomials up to degree 3 and converges much faster than simpler methods like the trapezoidal rule. The error decreases proportionally to h^4, meaning doubling the number of segments improves accuracy by roughly 16 times. This makes it an excellent choice for arc length calculations.
Can arc length be calculated for parametric curves?
Yes, parametric curves use a slightly different but closely related formula. For a curve defined by x = x(t) and y = y(t) where t ranges from t1 to t2, the arc length is L = integral from t1 to t2 of sqrt((dx/dt)^2 + (dy/dt)^2) dt. This is a natural generalization of the Cartesian formula. Parametric representation is actually more general, as it can describe curves that loop back on themselves or have vertical tangent lines, which cannot be expressed as y = f(x). For curves in three dimensions, defined by x(t), y(t), and z(t), you simply add (dz/dt)^2 under the square root. Arc Length by Integration Calculator handles Cartesian functions, which can be viewed as the special parametric case x(t) = t, y(t) = f(t).
What types of functions produce the longest arc lengths?
Functions with rapidly changing derivatives produce longer arc lengths relative to their chord length because the curve oscillates more, adding extra path length. Highly oscillatory functions like sine waves with large amplitudes and frequencies have substantially more arc length than their horizontal span. Exponential functions can also produce very long arcs as their derivatives grow quickly. For polynomial functions, higher-degree terms with large coefficients create more curvature and longer paths. The key insight is that arc length depends on the integrand sqrt(1 + [f'(x)]^2), so functions whose derivatives are large in magnitude contribute significantly to arc length. A flat line (derivative zero) has arc length exactly equal to the interval width.