/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 47 The curve defined by \(x=a \cos ... [FREE SOLUTION] | 91Ó°ÊÓ

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The curve defined by \(x=a \cos t, y=a \sin t, z=c t\) is a helix. Hold \(a\) fixed and use a CAS to obtain a parmetric plot of the helix for various values of \(c .\) What effect does \(c\) have on the curve?

Short Answer

Expert verified
Parameter \( c \) controls the vertical stretch or tightness of the helix; higher \( c \) values make it tighter vertically.

Step by step solution

01

Understand the Helix Equation

The given set of parametric equations defines the curve of a helix: \( x = a \cos t, y = a \sin t, z = ct \). Here, \( a \) is a constant, \( t \) is the parameter, and \( c \) is a variable parameter that influences the shape of the helix.
02

Analyze the Role of Variable 'c'

The parameter \( c \) influences the helix by stretching or compressing it along the vertical axis, which in this case, is aligned with the \( z \)-axis. A larger value of \( c \) results in a steeper and more tightly coiled helix, whereas a smaller value of \( c \) stretches the helix more gently.
03

Generate Parametric Plots Using a CAS

Use computer algebra systems (CAS) like Desmos or Python's Matplotlib to generate plots of the helical curve. Set \( a \) to a fixed value, such as \( 1 \), and plot the curve for different values of \( c \) (e.g., \( c = 0.5, 1, 2 \)). This helps visualize how the vertical stretch or compression changes the appearance of the helix.
04

Interpret the Plots

Examine the plots to see how variations in \( c \) impact the curve. Note that increasing \( c \) results in more rings per unit length along the \( z \)-axis, making the helix appear tighter, while decreasing \( c \) results in fewer rings over the same vertical distance.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Helix
The concept of a helix is fundamental in mathematics and geometry. A helix is a three-dimensional shape, like a spiral staircase, where the path twists uniformly around a cylinder. It can be visualized using the parametric equations:
  • \(x = a \cos t\)
  • \(y = a \sin t\)
  • \(z = ct\)
In these equations, \(a\) and \(c\) are constants, and \(t\) is a parameter that varies. The constants play essential roles: \(a\) determines the radius of the helix, deciding how far the helix reaches from its central axis, while \(c\) affects the pitch or the vertical distance each coil rises.
A helix can be found in many natural and engineered forms, such as in DNA structures or helical springs. Understanding its parameters helps in applications where geometric precision is crucial.
Computer Algebra Systems
Computer Algebra Systems (CAS) are powerful tools that assist with complex mathematical computations and visualizations. They are invaluable in learning environments because they provide dynamic representations and can perform algebraic manipulations that might be tedious by hand.
In plotting functions or curves like the helix, CAS like Desmos or Python's Matplotlib enable students to input parametric equations and immediately see the results. This real-time feedback helps deepen understanding, as students can quickly observe changes in the plot by adjusting parameters.
CAS also allows for exploration beyond plotting, including solving equations, differentiating, and integrating functions. Leveraging these tools helps students grasp intricate topics by offloading computation work and allowing focus on observation and learning.
Parametric Plots
Creating parametric plots is an excellent way to visualize functions defined with parameters. Unlike typical functions that rely solely on \(x\) and \(y\), parametric equations use a third variable, a parameter, usually \(t\), that expresses \(x\) and \(y\), and potentially \(z\) in three dimensions, independently.
For the helix, the parametric plot allows students to see how the path traces through space as \(t\) varies. This can be represented graphically using a range of tools, with CAS being among the most efficient. By setting \(a\) and varying \(c\) while running \(t\) through a range of values, students can see different shapes of the helix on the graph.
  • Visualize effects of different parameter values
  • Understand spatial trajectory of complex curves
  • Gain insights into the dynamic nature of mathematical systems
Understanding parametric plots is essential for topics like calculus, where visualization plays a significant role in comprehending complex behaviors.
Influence of Parameters
The influence of parameters in parametric equations is a central concept, as each parameter can significantly alter the resulting graph.
In the case of a helix defined by \(x = a \cos t\), \(y = a \sin t\), and \(z = ct\), the parameter \(c\) is crucial. It determines the pitch of the helix, or how much it stretches along the \(z\)-axis.
How Parameter 'c' Affects the Helix:
  • A larger \(c\) means the helix coils more tightly and rises faster.
  • A smaller \(c\) means each coil is more extended and less steep.
  • Changes to \(c\) directly impact the helix's appearance and can be easily visualized using a CAS.
By experimenting with different values, one can gain valuable insights into how mathematical models can be adapted for various practical applications. Adjusting parameters allows for a more in-depth exploration of mathematical systems and strengthens comprehension of dynamic behaviors in geometry.

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Most popular questions from this chapter

EXPL 48. In this exercise you will derive Kepler's First Law, that planets travel in elliptical orbits. We begin with the notation. Place the coordinate system so that the sun is at the origin and the planet's closest approach to the sun (the perihelion) is on the positive \(x\) -axis and occurs at time \(t=0\). Let \(\mathbf{r}(t)\) denote the position vector and let \(r(t)=\|\mathbf{r}(t)\|\) denote the distance from the sun at time \(t\). Also, let \(\theta(t)\) denote the angle that the vector \(\mathbf{r}(t)\) makes with the positive \(x\) -axis at time \(t\). Thus, \((r(t), \theta(t))\) is the polar coordinate representation of the planet's position. Let \(\mathbf{u}_{1}=\mathbf{r} / r=(\cos \theta) \mathbf{i}+(\sin \theta) \mathbf{j} \quad\) and \(\quad \mathbf{u}_{2}=(-\sin \theta) \mathbf{i}+(\cos \theta) \mathbf{j}\) Vectors \(\mathbf{u}_{1}\) and \(\mathbf{u}_{2}\) are orthogonal unit vectors pointing in the directions of increasing \(r\) and increasing \(\theta\), respectively. Figure 12 summarizes this notation. We will often omit the argument \(t\), but keep in mind that \(\mathbf{r}, \theta, \mathbf{u}_{1}\), and \(\mathbf{u}_{2}\) are all functions of \(t .\) A prime in. dicates differentiation with respect to time \(t\). (a) Show that \(\mathbf{u}_{1}^{\prime}=\theta^{\prime} \mathbf{u}_{2}\) and \(\mathbf{u}_{2}^{\prime}=-\theta^{\prime} \mathbf{u}_{1}\). (b) Show that the velocity and acceleration vectors satisfy $$ \begin{array}{l} \mathbf{v}=r^{\prime} \mathbf{u}_{1}+r \theta^{\prime} \mathbf{u}_{2} \\ \mathbf{a}=\left(r^{\prime \prime}-r\left(\theta^{\prime}\right)^{2}\right) \mathbf{u}_{1}+\left(2 r^{\prime} \theta^{\prime}+r \theta^{\prime \prime}\right) \mathbf{u}_{2} \end{array} $$ (c) Use the fact that the only force acting on the planet is the gravity of the sun to express a as a multiple of \(\mathbf{u}_{1}\), then explain how we can conclude that $$ \begin{aligned} r^{\prime \prime}-r\left(\theta^{\prime}\right)^{2} &=\frac{-G M}{r^{2}} \\ 2 r^{\prime} \theta^{\prime}+r \theta^{\prime \prime} &=0 \end{aligned} $$ (d) Consider \(\mathbf{r} \times \mathbf{r}^{\prime}\), which we showed in Example 8 was a constant vector, say D. Use the result from (b) to show that \(\mathbf{D}=r^{2} \theta^{\prime} \mathbf{k} .\) (e) Substitute \(t=0\) to get \(\mathbf{D}=r_{0} v_{0} \mathbf{k}\), where \(r_{0}=r(0)\) and \(v_{0}=\|\mathbf{v}(0)\|\). Then argue that \(r^{2} \theta^{\prime}=r_{0} v_{0}\) for all \(t\). (f) Make the substitution \(q=r^{\prime}\) and use the result from (e) to obtain the first-order (nonlinear) differential equation in \(q\) : $$ q \frac{d q}{d r}=\frac{r_{0}^{2} v_{0}^{2}}{r^{3}}-\frac{G M}{r^{2}} $$ (g) Integrate with respect to \(r\) on both sides of the above equation and use an initial condition to obtain $$ q^{2}=2 G M\left(\frac{1}{r}-\frac{1}{r_{0}}\right)+v_{0}^{2}\left(1-\frac{r_{0}^{2}}{r^{2}}\right) $$ (h) Substitute \(p=1 / r\) into the above equation to obtain $$ \frac{r_{0}^{2} v_{0}^{2}}{\left(\theta^{\prime}\right)^{2}}\left(\frac{d p}{d t}\right)^{2}=2 G M\left(p-p_{0}\right)+v_{0}^{2}\left(1-\frac{p^{2}}{p_{0}^{2}}\right) $$

find the tangential and normal components \(\left(a_{T}\right.\) and \(\left.a_{N}\right)\) of the acceleration vector at \(t .\) Then evaluate at \(t=t_{1} .\) $$ \mathbf{r}(t)=a \cos t \mathbf{i}+a \sin t \mathbf{j} ; t_{1}=\pi / 6 $$

\mathbf{F}(t)=\mathbf{f}(u(t)) .\( Find \)\mathbf{F}^{\prime}(t)\( in terms of \)t$ $$ \text { } \mathbf{f}(u)=u^{2} \mathbf{i}+\sin ^{2} u \mathbf{j} \text { and } u(t)=\tan t $$

Show that for a plane curve \(\mathbf{N}\) points to the concave side of the curve. Hint: One method is to show that $$ \mathbf{N}=(-\sin \phi \mathbf{i}+\cos \phi \mathbf{j}) \frac{d \phi / d s}{|d \phi / d s|} $$ Then consider the cases \(d \phi / d s>0\) (curve bends to the left) and \(d \phi / d s<0\) (curve bends to the right).

find the tangential and normal components \(\left(a_{T}\right.\) and \(\left.a_{N}\right)\) of the acceleration vector at \(t .\) Then evaluate at \(t=t_{1} .\) $$ \mathbf{r}(t)=(t+1) \mathbf{i}+3 t \mathbf{j}+t^{2} \mathbf{k} ; t_{1}=1 $$

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