Name: horizontal slices for area between curves
Uploaded: 2026-07-24T11:47:53.303Z
Duration: 1 min 30 s
Channel: JoVE

Considérons une région délimitée par deux courbes, chacune exprimée en fonction de y.La frontière gauche et la bordure droite, toutes deux fonctions, sont continues sur l’intervalle de y=c à y=d.Ces lignes horizontales définissent l’étendue verticale de la région.Pour montrer l’aire, on utilise la méthode de la somme de Riemann. La région est divisée en fines bandes horizontales d’égal hauteur Δy et une base égale à la distance horizontale entre les deux courbes de bord. La surface totale estimée est déterminée en additionnant les surfaces de tous les rectangles fins. Lorsque Δy devient infinitésimalement petit, l’aire totale est obtenue en intégrant la distance horizontale par rapport à y.Cette méthode est utilisée lorsque les courbes frontières sont décrites en termes de y.Considérons une condition d’équilibre vapeur-liquide dans un mélange où la phase liquide, x, et la phase vapeur, y, coexistent dans un état d’équilibre. Dans le graphique, il y a deux courbes : la courbe diagonale et la courbe d’équilibre.Cette aire enfermée est calculée à l’aide de l’intégrale de l’axe y. Le résultat est la surface totale de séparabilité, ce qui permet de séparer les composants sur toute la plage de composition.

aire comprise entre deux courbes : intégration par rapport à y

Area Between Curves: Integrating With Respect to y

Consid&#xE9;rez une r&#xE9;gion plane d&#xE9;limit&#xE9;e par deux courbes exprim&#xE9;es comme des fonctions de la variable verticale y. Les courbes limites gauche et droite sont continues entre y = c et y = d, et ces deux droites horizontales d&#xE9;finissent les limites verticales de la r&#xE9;gion. &#xC9;tant donn&#xE9; que les fronti&#xE8;res d&#xE9;pendent de y plut&#xF4;t que de x, l&#x2019;aire est le plus souvent &#xE9;valu&#xE9;e &#xE0; l&#x2019;aide de tranches horizontales.
L&#x2019;aire est calcul&#xE9;e &#xE0; l&#x2019;aide de la m&#xE9;thode des sommes de Riemann. La r&#xE9;gion est subdivis&#xE9;e en plusieurs bandes horizontales minces, chacune de hauteur identique, not&#xE9;e &#x394;y. Pour chaque bande, la largeur correspond &#xE0; la distance horizontale entre la courbe fronti&#xE8;re droite et la courbe fronti&#xE8;re gauche &#xE0; une valeur donn&#xE9;e de y. Chaque bande forme ainsi un rectangle mince, dont l&#x2019;aire est obtenue en multipliant sa hauteur par cette distance horizontale. La somme des aires de l&#x2019;ensemble de ces rectangles fournit une approximation de l&#x2019;aire totale de la r&#xE9;gion. Lorsque l&#x2019;&#xE9;paisseur des bandes diminue et tend vers z&#xE9;ro, cette approximation devient exacte, et l&#x2019;aire totale est alors obtenue en int&#xE9;grant, par rapport &#xE0; y, la distance horizontale s&#xE9;parant les deux courbes. Cette approche est particuli&#xE8;rement adapt&#xE9;e lorsque la g&#xE9;om&#xE9;trie de la r&#xE9;gion est d&#xE9;crite de mani&#xE8;re plus naturelle en fonction de y.
Cette m&#xE9;thode a une pertinence directe dans l&#x2019;analyse du comportement &#xE0; l&#x2019;&#xE9;quilibre liquide&#x2013;vapeur des m&#xE9;langes. Dans de tels syst&#xE8;mes, les compositions de la phase liquide et de la phase vapeur sont en &#xE9;quilibre. Un diagramme d&#x2019;&#xE9;quilibre typique comprend une droite diagonale repr&#xE9;sentant l&#x2019;&#xE9;galit&#xE9; des compositions de la vapeur et du liquide, ainsi qu&#x2019;une courbe d&#x2019;&#xE9;quilibre traduisant la relation de phase entre les deux phases. La r&#xE9;gion comprise entre ces deux courbes repr&#xE9;sente l&#x2019;&#xE9;cart entre les compositions de la vapeur et du liquide sur l&#x2019;ensemble de la gamme de compositions. Lorsque cette r&#xE9;gion est &#xE9;valu&#xE9;e par int&#xE9;gration horizontale, l&#x2019;aire calcul&#xE9;e est appel&#xE9;e aire totale de s&#xE9;parabilit&#xE9;. Cette aire constitue une mesure quantitative du potentiel de s&#xE9;paration des composants du m&#xE9;lange, des aires plus &#xE9;lev&#xE9;es indiquant une capacit&#xE9; de s&#xE9;paration accrue dans des conditions d&#x2019;&#xE9;quilibre.

Aire comprise entre deux courbes : intégration par rapport à y

Consid&#xE9;rez une r&#xE9;gion plane d&#xE9;limit&#xE9;e par deux courbes exprim&#xE9;es comme des fonctions de la variable verticale y. Les courbes ...

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area-between-curves-integrating-with-respect-to-y

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Calculus

Calcul

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Applications of Integration

Applications de l'intégration

KEY TERMS AND CONCEPTS

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horizontal slices for area between curves

Area between curves can be found with horizontal slices when both boundaries are written as functions of y. The left and right curves are continuous from y = c to y = d, and those lines set the vertical limits of the region. Because the curves depend on y, the area is best measured by moving across the shape with thin horizontal strips.

The method uses a Riemann sum. The region is divided into many thin strips with the same height, delta y. For each strip, the width is the horizontal distance between the right boundary curve and the left boundary curve at a chosen value of y. Each strip is a thin rectangle, so its area is height times width.

Adding the areas of all the rectangles gives an approximation of the total area. As the strips become thinner and approach zero, the approximation becomes exact. The area is then found by integrating the horizontal distance between the curves with respect to y.

This approach is useful when a region is easier to describe with y than with x. It also connects to vapor-liquid equilibrium in mixtures. In that setting, the liquid-phase composition and the vapor-phase composition exist together in equilibrium.

A typical equilibrium diagram includes a diagonal line where vapor and liquid compositions are equal. It also includes an equilibrium curve that shows the phase relationship between the two phases. The region between these curves shows the difference between vapor and liquid compositions across the full composition range.

When this enclosed region is measured using horizontal integration, the result is called the total separability area. This area gives a way to measure how well the components of a mixture may be separated under equilibrium conditions. A larger area suggests greater separation capability.

Horizontal Slices for Area Between Curves

horizontal-slices-for-area-between-curves

area between curves: integrating with respect to x

area-between-curves-integrating-with-respect-to-x

Vertical Slices for Area Between Curves

Area between curves can be found by using vertical slices and a definite integral. For two continuous functions on a closed interval from a to b, the region is bounded by their graphs on the sides and by the interval endpoints across the bottom and top edges of the setup. A first estimate comes from splitting the interval into many narrow vertical strips of equal width. Each strip is treated like a rectangle. Its height is the vertical difference between the two functions at a chosen point...

area between curves: integrating with respect to y

Area between curves can be found with horizontal slices when both boundaries are written as functions of y. The left and right curves are continuous from y = c to y = d, and those lines set the vertical limits of the region. Because the curves depend on y, the area is best measured by moving across the shape with thin horizontal strips. The method uses a Riemann sum. The region is divided into many thin strips with the same height, delta y. For each strip, the width is the horizontal distance...

area between curves: problem solving

Piecewise Area Between Curves

Piecewise area between curves uses more than one integral to find the size of a region on a graph. In this example, the region is enclosed by a square root function, a reflected cube root function, and a linear function. The line intersects each of the other two curves, and those intersection points show where the boundary of the region changes. The area cannot be found with one setup over the full interval because the top and bottom curves are not the same everywhere. The region is split at...

calculation of volume of solids by integration

calculation-of-volume-of-solids-by-integration

Slicing Methods for Solid Volume

Slicing methods help find the volume of solids with changing cross-sections. A basic solid, like a rectangular box, is easy to measure because its base area stays the same along its height. Many real objects do not have that regular shape, so elementary geometry is not enough. The slicing method solves this by breaking a solid into many very thin slices. These slices are taken perpendicular to a chosen axis, often the x-axis. Each slice has a small thickness, written as delta x, and a...

volumes of solids of revolution

Disk Method for Rotated Region Volume

The disk method is used to find the volume of a solid formed by rotating a region around an axis. The region is first drawn in a two-dimensional plane. When that region spins around a fixed line, called the axis of revolution, it creates a three-dimensional shape with rotational symmetry. These shapes appear often in math models, physics, and engineering. When the region touches the axis of revolution, the solid has no hollow space inside. Its cross-sections are circular, so the shape can be...

finding volume using cross-sectional area

finding-volume-using-cross-sectional-area

Tetrahedron Volume from Triangle Slices

Tetrahedron volume can be found by adding the areas of triangular slices. This method uses cross-sectional area, which is the area of a flat slice taken through a 3D solid. It is useful when a solid changes shape in a regular way and a simple geometric formula is not available. A tetrahedron is a good example. It has a height h and an equilateral triangle base with side length a. The coordinate system places the origin at the top vertex, and the y-axis goes downward along the height to the...

problem solving: volume

Finding the Volume of a Jet Fuel Tank

The volume of a jet fuel tank can be found with solids of revolution. The tank is modeled by rotating a two-dimensional region around the x-axis. This creates a three-dimensional shape that is symmetric about the axis of rotation. The region runs from 0 to 2 meters, so the tank’s shape can be measured along that length. Because the boundary curve touches the axis, the disk method works well here. The disk method breaks the solid into many very thin circular slices that are perpendicular to the...

average value of a function

Estimating Function Behavior with Average Value

The average value of a function gives one number that summarizes how a quantity changes over a closed interval. It can also be viewed as the height of a rectangle whose area matches the net area under the curve. That net area includes both positive and negative parts of the function, so the result reflects the function’s overall behavior. A greenhouse temperature over a 24-hour period is a practical example of this idea. The temperature may rise and fall throughout the day, but it is still...

key terms and concepts

Learn how to find area between curves using horizontal slices, Riemann sums, and integration with respect to y, with a vapor-liquid equilibrium example.

Horizontal Slices for Area Between Curves | 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

Horizontal Slices for Area Between Curves

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