Application Of Integral Calculus

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AIM OF THE EXPLORATION

ÿ Explore Integral Calculus usage to find the Volume of the solids

ÿ Identify the cross-section of the solid

ÿ Suggest an Algorithm for finding an expression for the Volume

INTRODUCTION

We learnt in the Applications of the Integral calculus to find the area under the curve.

This can be divided in following three cases:

ÿ Area below any given curve and above the X-axis

ÿ Area between the two given curves

If definite integration can be used to calculate the area of any figure in XY plane, then there must be

some way to calculate the volume of Figures in 3 Dimensional Geometry. can calculus be used for this

purpose.

Yes definitely, and that is the topic of our exploration. We will try to demonstrate the use of calculus

or Definite Integration to find the volume of certain figures having the cross-sections whose area we

already know.

We will take 4 cases:

ÿ Solid with cross-section of a square

ÿ Solid with cross-section of a equilateral triangle

ÿ Solid with cross-section of a circle

ÿ Solid with cross-section of a rectangle

To demonstrate the use of calculus, we will be taking certain examples and solving them

MATHEMATICAL DEMONSTRATION

The Simplest Case—One curve with the area entirely above the x-axis

The example of this type is the region in the first quadrant bounded by , x-axis

and .

Begin with a sketch of the problem. The dark line represents the ith rectangle.

The curve clearly passes through x=0, so x=0 is the lower bound of the definite integral.

.

The top curve is and the bottom curve is y=0 so the integral we need is

Area between two curves

the area between two curves f and g from a to b is given by

f (x) ≥ g(x) ∀ x ∈ (a,b)

This integral will always yield the ...

... middle of paper ...

...ce as seen from "above".

The area of a rectangle is base times height.

The base of our rectangle = the distance from f to g which is 2 .

The area of the cross section = 4 . The thickness is dx

The volume of our slice is 4 dx .

The required volume will be given by,

INFERENCE

Algorithm to derive an expression for the volume of the solids with known cross-sections is as follows.

ÿ The region of the base of the solid is drawn

ÿ An arbitrarily chosen slice of the solid with the desired orientation is drawn and the

thickness is denoted as dx or dy

ÿ The shape of the cross section is drawn

ÿ Measure the parameters of the solid in terms of x or y looking at the base.

ÿ Write dV , the volume of one arbitrary slice using geometry formulas.

ÿ Use the integral for the volume V, by seeing at the base to determine where the slices

start and stop.

ÿ Evaluate.

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