5.7
喷气式飞机机翼上安装的燃料箱体积可借助旋转体的概念进行刻画。在该情境中,燃料箱由一个二维区域绕 x 轴旋转生成;该区域由某一函数的图像所界定,并沿 x 轴从 0 延伸至 2 m。旋转后所得三维形体关于旋转轴对称。由于边界曲线与 x 轴相贴,因此采用圆盘法求体积是恰当的。
采用圆盘法时,可将该旋转体在…
安装在喷气式飞机机翼上的燃料箱是通过将一个区域绕中心轴旋转而成。该区域由一个数学函数绕x轴旋转形成,其范围从零延伸至两米。
为了求出该容器的体积,采用圆盘法,即将该立体沿垂直于 x 轴的方向切割成无数个无限薄的圆形圆盘。
每个圆盘的面积等于函数值的平方乘以 ��。通过在该区间上对这些面积进行积分,可求得总体积。
对函数平方后,被积函数简化为一个常数乘以 x 的二次方,再乘以 2 与 x 的差。
展开并积分该表达式可得到一个包含 x 的三次方和四次方的原函数。
计算从 0 到 2 的定积分并代入上下限后得到一个表达式。进一步化简可得体积约为 1 立方米,即该燃料箱的总体积。
View the full transcript and gain access to JoVE Core videos
Q1: What is the disk method and how does it apply to finding volume?
The disk method divides a solid of revolution into infinitesimally thin circular disks perpendicular to the axis of rotation. Each disk's area equals π times the square of the function's radius value. By integrating these disk areas over the specified interval, you accumulate the total volume of the solid using calculation of volume of solids by integration.
Q2: How is a fuel tank modeled as a solid of revolution?
A fuel tank is modeled by rotating a two-dimensional region defined by a mathematical function about the x-axis. The region extends from zero to two meters along the axis, creating a three-dimensional symmetric shape. This approach allows engineers to calculate precise fuel capacity and weight distribution for aircraft performance.
Q3: What steps are involved in calculating the volume using integration?
First, square the function defining the tank's boundary to get the disk area formula. Then expand the resulting expression to identify terms with third and fourth powers of the variable. Finally, integrate these terms over the interval from zero to two meters and evaluate the definite integral by substituting the limits.
Q4: Why is the disk method appropriate for this fuel tank problem?
The disk method is appropriate because the boundary curve lies directly against the axis of rotation, creating circular cross-sections perpendicular to the x-axis. This geometry allows each disk's radius to equal the function value at that position, making the method straightforward and accurate for calculating the tank's volume.
Q5: What does the antiderivative represent in this volume calculation?
The antiderivative describes how volume accumulates along the axis of integration as you move from zero to two meters. It captures the cumulative effect of all infinitesimal disk areas stacked along the tank's length. Evaluating this antiderivative at the limits yields the total internal capacity of approximately one cubic meter.
Q6: How does the definite integral produce the final volume result?
The definite integral evaluates the antiderivative at the upper limit of two meters and subtracts its value at the lower limit of zero. This calculation yields a numerical result that simplifies to approximately one cubic meter, representing the total fuel tank capacity needed for aerospace engineering applications.
Q7: Why is precise volume calculation critical in aerospace engineering?
Accurate volume estimates determine fuel capacity, weight distribution, and overall aircraft performance. Engineers must know exact tank dimensions to optimize fuel storage, balance aircraft weight, and ensure safe flight operations. Mathematical modeling through integration provides the precision necessary for reliable aerospace design and safety.