Name: calculating surface area from rotation
Uploaded: 2026-01-12T12:24:30.000Z
Duration: 1 min 29 s
Channel: JoVE

Pour garantir qu’un moteur-fusée résiste à des températures extrêmes, les ingénieurs doivent appliquer une couche précise de revêtement résistant à la chaleur sur sa buse en forme de cloche.Estimer la quantité exacte de matériau nécessaire nécessite de calculer la surface totale de révolution.Considérons le profil de la buse comme une fonction courbe dans un plan bidimensionnel. Faire tourner cette courbe autour de l’axe des x génère la surface de révolution 3D.Pour calculer l’aire exacte, la courbe est divisée en petits sous-intervalles approximés par des lignes droites. Faire tourner chaque segment droit autour de l’axe forme une bande conique étroite.La surface d’une bande unique est calculée en multipliant sa circonférence par sa hauteur inclinée. Comme le rayon varie sur la bande, le calcul utilise un rayon moyen.Simultanément, la hauteur inclinée est calculée à l’aide de la longueur d’arc de la courbe le long de ce segment. Cela explique la pente de la buse.Enfin, la somme des aires de ces bandes fournit une approximation. À mesure que les segments deviennent infiniment étroits, le rayon moyen converge vers la valeur de la fonction. Cette limite transforme la somme en une intégrale définie, donnant la surface précise.

aire d’une surface de révolution

Area of a Surface of Revolution

Les surfaces de r&#xE9;volution sont form&#xE9;es par la rotation d&#x2019;une courbe bidimensionnelle autour d&#x2019;un axe, cr&#xE9;ant une forme tridimensionnelle. Ce concept est utilis&#xE9; en ing&#xE9;nierie, notamment pour d&#xE9;terminer l&#x2019;aire de la surface d&#x2019;une tuy&#xE8;re de fus&#xE9;e, o&#xF9; des calculs pr&#xE9;cis sont essentiels pour l&#x2019;application uniforme de rev&#xEA;tements r&#xE9;sistants &#xE0; la chaleur. La courbe, lorsqu&#x2019;elle est mise en rotation autour de l&#x2019;axe des abscisses, d&#xE9;crit une surface continue dont l&#x2019;aire doit &#xEA;tre calcul&#xE9;e avec pr&#xE9;cision afin d&#x2019;estimer les besoins en mat&#xE9;riaux.
Approximation par bandes coniques
Pour estimer l&#x2019;aire de la surface, la courbe est d&#x2019;abord divis&#xE9;e en petits segments de droite sur de courts intervalles. Lorsque ces segments sont mis en rotation autour de l&#x2019;axe, ils forment des bandes coniques &#xE9;troites. L&#x2019;aire de chaque bande est approxim&#xE9;e en multipliant sa circonf&#xE9;rence moyenne par la g&#xE9;n&#xE9;ratrice, qui refl&#xE8;te la longueur et la pente de ce segment. Le rayon moyen de chaque bande est calcul&#xE9; &#xE0; partir des valeurs de la fonction d&#x2019;origine dans l&#x2019;intervalle consid&#xE9;r&#xE9;, et la g&#xE9;n&#xE9;ratrice est obtenue &#xE0; partir de la longueur de l&#x2019;arc de la courbe.
Affinage vers une valeur exacte
&#xC0; mesure que les segments deviennent de plus en plus &#xE9;troits, l&#x2019;approximation devient plus pr&#xE9;cise. &#xC0; la limite, lorsque la largeur des intervalles tend vers z&#xE9;ro, l&#x2019;aire totale de la surface s&#x2019;exprime par une int&#xE9;grale d&#xE9;finie. Cette int&#xE9;grale combine le rayon variable et la pente de la courbe, restituant ainsi la g&#xE9;om&#xE9;trie r&#xE9;elle de la surface. Cela donne une valeur pr&#xE9;cise de l&#x2019;aire de la surface, essentielle pour des applications critiques telles que la protection thermique en ing&#xE9;nierie a&#xE9;rospatiale.

Aire d’une surface de révolution

Les surfaces de r&#xE9;volution sont form&#xE9;es par la rotation d&#x2019;une courbe bidimensionnelle autour d&#x2019;un axe, cr&#xE9;ant une forme ...

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

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 piece forms a narrow conical band, which is a thin ring-like section of a cone. The area of each band is estimated using its average circumference and its slant height, which is the tilted length of that segment.

The radius for each band comes from the function values over the interval. The slant height comes from the arc length of the curve. As the intervals become smaller, the estimate becomes more accurate. In the limit, the surface area is written as a definite integral.

This integral includes the changing radius and the slope of the curve. It captures the true shape of the surface instead of a rough estimate. The final result gives a precise surface area value. That precision is important in high-stakes work such as thermal protection for aerospace parts.

Calculating Surface Area from Rotation

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

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 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...

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 rotating a curve around the x-axis creates a surface and how conical bands lead to a definite integral for exact surface area.

Calculating Surface Area from Rotation | 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

Calculating Surface Area from Rotation

Description

Transcript

Tags