Name: pappus theorem for volume and surface area
Uploaded: 2026-01-12T12:24:33.000Z
Duration: 1 min 24 s
Channel: JoVE

Le théorème de Pappus pour le volume relie la géométrie d’une région plane au volume de son solide de révolution, sans utiliser de techniques d’intégration comme la méthode du disque.Le théorème affirme que lorsqu’une région plane avec un centroïde connu tourne autour d’un axe, le volume résultant est égal à l’aire de la région multipliée par la distance parcourue par son centroïde le long du trajet circulaire.Par exemple, considérons une forme tridimensionnelle qui ressemble à un donut, appelée tore. Il se forme en faisant tourner un cercle de rayon r autour d’une droite dans son plan qui ne coupe pas le cercle.Cette section circulaire génère le solide lors de la rotation.Le centroïde du cercle se trouve à une distance R de l’axe de rotation.Au fur et à mesure que le cercle tourne, son centroïde suit un trajet circulaire d’une longueur égale à sa circonférence.En utilisant le théorème, le volume du tore est déterminé en multipliant l’aire de la section transversale par la distance parcourue par le centroïde.Un exemple pratique est l’utilisation de réservoirs toroïdaux pour stocker le carburant dans des espaces étroits. Le théorème de Pappus utilise la surface et la longueur du chemin du centroïde pour trouver le volume, ce qui aide à déterminer la capacité de carburant disponible.

théorème de pappus

Theorem of Pappus

Le th&#xE9;or&#xE8;me de Pappus, &#xE9;galement connu sous le nom de th&#xE9;or&#xE8;me de Pappus-Guldinus, fournit une m&#xE9;thode g&#xE9;om&#xE9;trique pour d&#xE9;terminer le volume et l&#x2019;aire de surface des solides engendr&#xE9;s par la rotation d&#x2019;une r&#xE9;gion plane ou d&#x2019;une courbe plane autour d&#x2019;un axe ext&#xE9;rieur. Ce th&#xE9;or&#xE8;me se compose de deux &#xE9;nonc&#xE9;s li&#xE9;s. Le premier concerne le volume des solides form&#xE9;s par la rotation de r&#xE9;gions planes, tandis que le second concerne l&#x2019;aire de surface engendr&#xE9;e par la rotation de courbes planes. Ces deux r&#xE9;sultats d&#xE9;pendent de la position du centre de gravit&#xE9;, qui repr&#xE9;sente la position moyenne de l&#x2019;aire ou de la courbe.Le premier th&#xE9;or&#xE8;me de Pappus stipule que le volume V d&#x2019;un solide form&#xE9; par la rotation d&#x2019;une r&#xE9;gion plane autour d&#x2019;un axe ext&#xE9;rieur &#xE0; cette r&#xE9;gion est &#xE9;gal au produit de l&#x2019;aire A de la r&#xE9;gion et de la distance parcourue par son centre de gravit&#xE9; lors d&#x2019;une r&#xE9;volution compl&#xE8;te. Cette relation est donn&#xE9;e par<figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:25%;"><img style="aspect-ratio:300/24;" src="https://cloudfront.jove.com/files/ftp_upload/40592/40592_Equation_1_editor_40592.svg" alt="40592_Equation_1.svg" /></figure>o&#xF9; d est la distance perpendiculaire entre le centre de gravit&#xE9; de la r&#xE9;gion et l&#x2019;axe de rotation.Consid&#xE9;rons un demi-cercle de rayon r, que l&#x2019;on fait tourner autour de son diam&#xE8;tre. L&#x2019;aire du demi-cercle est A = 1/2&#x3C0;r^2, et la distance entre son centre de gravit&#xE9; et son diam&#xE8;tre est d = 4r/3&#x3C0;. En substituant ces valeurs, on obtient<figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:25%;"><img style="aspect-ratio:300/48;" src="https://cloudfront.jove.com/files/ftp_upload/40592/40592_Equation_2_editor_40592.svg" alt="40592_Equation_2.svg" /></figure>qui correspond &#xE0; la formule classique du volume d&#x2019;une sph&#xE8;re.Le deuxi&#xE8;me th&#xE9;or&#xE8;me de Pappus stipule que l&#x2019;aire de surface S engendr&#xE9;e par la rotation d&#x2019;une courbe plane autour d&#x2019;un axe ext&#xE9;rieur est &#xE9;gale &#xE0; la longueur d&#x2019;arc L de la courbe multipli&#xE9;e par la distance parcourue par son centre de gravit&#xE9;. Ceci est exprim&#xE9; par<figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:25%;"><img style="aspect-ratio:300/24;" src="https://cloudfront.jove.com/files/ftp_upload/40592/40592_Equation_3_editor_40592.svg" alt="40592_Equation_3.svg" /></figure>&#xC0; titre d&#x2019;exemple, consid&#xE9;rons un cercle de rayon r dont le centre est situ&#xE9; &#xE0; une distance R de l&#x2019;axe de rotation. La rotation de ce cercle autour de l&#x2019;axe produit un tore. La longueur de l&#x2019;arc du cercle est L = 2&#x3C0;r, et le centre de gravit&#xE9; d&#xE9;crit une trajectoire circulaire de longueur 2&#x3C0;R. L&#x2019;application du th&#xE9;or&#xE8;me donne<figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:25%;"><img style="aspect-ratio:300/24;" src="https://cloudfront.jove.com/files/ftp_upload/40592/40592_Equation_4_editor_40592.svg" alt="40592_Equation_4.svg" /></figure>Ces th&#xE9;or&#xE8;mes permettent un calcul efficace des volumes et des aires de surface sans int&#xE9;gration explicite, &#xE0; condition de conna&#xEE;tre les positions des centres de gravit&#xE9; et les mesures g&#xE9;om&#xE9;triques. En ing&#xE9;nierie et en sciences appliqu&#xE9;es, le th&#xE9;or&#xE8;me de Pappus-Guldinus est largement utilis&#xE9; pour l&#x2019;analyse des solides de r&#xE9;volution, tels que les r&#xE9;servoirs, les d&#xF4;mes et les canalisations, contribuant ainsi &#xE0; une conception pr&#xE9;cise et &#xE0; une estimation des mat&#xE9;riaux.

Théorème de Pappus

Le th&#xE9;or&#xE8;me de Pappus, &#xE9;galement connu sous le nom de th&#xE9;or&#xE8;me de Pappus-Guldinus, fournit une m&#xE9;thode g&#xE9;om&#xE9;trique ...

Education

Enseignement

JoVE Core

Calculus

Calcul

Unit

Unité

Application of Techniques of Integration

Application des techniques d'intégration

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

pappus theorem for volume and surface area

Pappus Theorem connects centroid motion to the volume and surface area of solids of revolution. It is also called the Pappus–Guldinus Theorem. The method uses geometry to find these values when a plane region or a plane curve is rotated about an external axis.

The theorem has two related parts. The first part gives the volume of a solid formed by rotating a plane region around an axis outside the region. In this case, the volume equals the area of the region multiplied by the distance traveled by its centroid in one full turn. The distance d is the perpendicular distance from the centroid to the axis of rotation.

A semicircle shows how the first theorem works. For a semicircle of radius r, the area is 1/2 r^2. Its centroid is 4r/3 from the diameter. When these values are used, the result matches the classical formula for the volume of a sphere.

The second part of the theorem gives the surface area made by rotating a plane curve about an external axis. Here, the surface area equals the arc length of the curve multiplied by the distance traveled by its centroid. The arc length is the length of the curve, and the centroid again follows a circular path during rotation.

A circle provides the second example. For a circle of radius r whose center is a distance R from the axis, rotation forms a torus. The circle has arc length 2r, and its centroid travels a path of length 2R. Using the theorem gives the surface area of the torus.

These theorems help students and engineers find volumes and surface areas without direct integration, as long as the centroid location and geometric measurements are known. They are useful in applied science for shapes such as tanks, domes, and pipes. That makes the Pappus–Guldinus Theorem a practical tool for design and material estimation.

Pappus Theorem for Volume and Surface Area

pappus-theorem-for-volume-and-surface-area

arc length of a curve

Measuring Curved Paths with Calculus

Measuring curved paths with calculus is important in engineering projects. Roller coaster tracks, cables, and railway lines often follow smooth curves instead of straight lines. Accurate path length helps with planning and design. A curve is first split into small segments. Each short segment is treated as a straight line between two nearby points on the curve. Adding these line segments gives an estimate of the total distance along the path. The estimate becomes better when the segments are...

arc length of a curve: problem solving

Catenary Cable Length in Power Lines

Catenary cable length helps engineers measure the full span of a hanging power line. A high-voltage line stretches 40 meters between two transmission towers and sags 10 meters because of gravity and thermal expansion. The cable forms a catenary, which is the curve of a uniform, flexible cable under its own weight. A catenary is not the same as a parabola. It is described by the hyperbolic cosine function, which gives a more accurate shape for a suspended cable. In this setup, engineers use the...

arc length function

Measuring Distance Along a Curve

The arc length function measures the distance traveled along a smooth curve from a fixed starting point to a moving endpoint. It is useful when a straight-line estimate is not accurate enough. For curves that are continuous and differentiable, arc length gives a precise way to track length along the curve. To find this distance, the curve is broken into many small pieces. Each piece is treated like a short straight line. Its length depends on the horizontal change and the vertical change over...

area of a surface of revolution

Calculating Surface Area from Rotation

Surfaces of revolution are created when a two-dimensional curve is rotated around an axis. The rotation produces a three-dimensional shape. In engineering, this calculation can help determine the surface area of a rocket nozzle. That information matters when a heat-resistant coating must be applied evenly. When a curve is revolved about the x-axis, it sweeps out a continuous surface. To find its area, the curve is first broken into small straight-line pieces over short intervals. Each rotated...

applications of integration to find hydrostatic pressure

applications-of-integration-to-find-hydrostatic-pressure

Hydrostatic Force on Dam Walls with Integration

Hydrostatic force is the total force a fluid at rest exerts on a surface. For a horizontal surface at a fixed depth, the pressure is constant. It is found by multiplying fluid density, gravitational acceleration, and depth. A vertical dam wall is different because pressure increases with depth. The water above each point adds to the pressure below it. That means the force is not spread evenly across the wall. Integration helps measure this changing force. Pressure in a still fluid rises...

applications of integration to find centers of mass

applications-of-integration-to-find-centers-of-mass

Center of Mass in Discrete and Continuous Systems

Center of mass can be found from rotational equilibrium and from integration. A balanced plank on a pivot shows the idea clearly. When the net torque about the pivot is zero, the system is in balance. Torque is the force on an object times its perpendicular distance from the pivot. At that point, the pivot lies at the center of mass. For a set of discrete point masses, the center of mass is the position where the masses balance by weight. Each mass contributes its mass times its position,...

theorem of pappus

Pappus Theorem connects centroid motion to the volume and surface area of solids of revolution. It is also called the Pappus–Guldinus Theorem. The method uses geometry to find these values when a plane region or a plane curve is rotated about an external axis. The theorem has two related parts. The first part gives the volume of a solid formed by rotating a plane region around an axis outside the region. In this case, the volume equals the area of the region multiplied by the distance traveled...

applications of integration to find consumer surplus

applications-of-integration-to-find-consumer-surplus

Consumer Surplus from Demand and Integration

Consumer surplus measures the economic gain buyers receive when they pay less than the highest price they are willing to pay. In microeconomics, this idea comes from the demand function, which links quantity to the price consumers will pay. Because willingness to pay usually falls as quantity rises, the demand curve slopes downward. When a product is sold at a fixed price, some buyers would have paid more for the first units they bought. The difference between that willingness to pay and the...

applications of integration to find blood flow

applications-of-integration-to-find-blood-flow

Using Integration to Model Blood Flow

Blood flow in a cylindrical blood vessel can be modeled with integration and laminar flow. Laminar flow is smooth motion in parallel layers. In this model, blood speed changes with distance from the center of the vessel. The blood moves fastest along the central axis. As the distance from the center increases, the velocity decreases. At the vessel wall, the velocity drops to zero because of viscous drag. This changing speed across the cross-section is the key idea behind the calculation. To...

introduction to normal distributions

Normal Distribution in Test Scores

Normal distribution helps explain how standardized test scores can be spread across a group. It is a key idea in statistics for describing symmetry, center, and variability in large sets of data. Test score data often start as a histogram. In a histogram, each bar shows how many scores fall within a score range. To turn that count-based graph into a continuous probability model, the histogram is normalized by dividing each bar height by the total number of observations and by the bin width. <br...

applications of integration to probability density functions

applications-of-integration-to-probability-density-functions

Finding Probability with Area Under a PDF

Continuous probability distributions describe random variables that can take any real value within a set range. Height is one example, since it can be measured with growing precision, such as 163.5 or 165.25 centimeters. That makes height a continuous random variable. The pattern of a continuous random variable is shown with a probability density function, or PDF. A PDF shows how probability is spread across the possible values. In a continuous distribution, probabilities are assigned to...

key terms and concepts

Learn how the Pappus–Guldinus Theorem uses centroid motion to find the volume of solids and surface area of rotated curves, with sphere and torus examples.

Pappus Theorem for Volume and Surface Area | JoVE K12

The JoVE Core Calculus collection provides a comprehensive visual guide to the entire calculus sequence, seamlessly connecting mathematical theory to real-world applications in physics and economics. Through dynamic animated lessons, the course transitions smoothly from foundational single-variable concepts to advanced multivariable topics. Students will explore everything from standard differentiation and integration to spatial vectors, multi-dimensional derivatives, and complex vector fields. By breaking down abstract coordinate systems, infinite series, and spatial motion, this structured approach builds the robust analytical skills and advanced mastery essential for STEM success.

calculus

Pappus Theorem for Volume and Surface Area

Description

Transcript

Tags