Module 12  Particle Motion and Parametric Models  
Introduction  Lesson 1  Lesson 2  Lesson 3  SelfTest  
Lesson 12.1: Motion Along a Line  
In this lesson you will model the motion of a particle that moves along the xaxis by using parametric equations. The motion of the particle will be illustrated by using the TI89 to show animated movement. You will also see that parametric equations that model a particle's movement are not unique by developing different parametric equations to model the same movement. A particle moves along the xaxis so that its position is given by the equation below, where t represents time in seconds. x(t) = 2t^{3} – 9t^{2} + 12t + 1
You can use your TI89 to visualize the motion of the particle and determine when the particle is at rest, when it is moving to the right, and when it is moving to the left. To graph parametric equations on the
Entering the Parametric Function
Instead of entering y as a function of x you will enter x and y as functions of t. Because x and y are both functions of a common parameter t, these equations are called parametric equations.
Setting the Graph Style to Animate You can view an animation of the particle's motion by changing the Graph Style of xt1 to animate.
Setting the Viewing Window
In addition to the minimum and maximum values for x and y there is a third variable in this menu, t.
With the values shown, t will initially be 0 and then increase by steps of one tenth until it is 4. For each value of t the position of the particle, as determined by the corresponding x and yvalues, will be plotted. xmin, xmax, ymin and ymax determine what part of the xyplane will be shown in the viewing window the same way they do in FUNCTION graphing mode.
You should see a circle move along the xaxis. This circle follows the path of the particle over the time interval from t = 0 to t = 4. You can see the graph again by pressing to Regraph. Using the Trace Feature The Trace feature can produce a similar animated effect.
Try pressing the left or right arrow and holding it down. Tracing Time Notice that the key moves the particle forward in time, which may not always coincide with motion to the right and that the key moves the cursor back in time, which may not always coincide with motion to the left. The value of t and the x and y coordinates are shown at the bottom of the screen.
12.1.1 Use the cursor movement keys to estimate when the particle is moving to the right.
12.1.2 Estimate when the particle is moving to the left.
12.1.3 When does the particle appear to change direction? Visualizing the Path over Time The animation on the xaxis is a fairly realistic model for the motion of the particle, however it is difficult to see the time intervals when the particle moves left and moves right. Make the following additions in the Y= Editor to help visualize the motion of the particle over the six seconds.
Setting the Graph Style
Setting the Graph Order
SIMUL stands for simultaneous mode in which all the selected functions will be graphed at the same time.
Displaying the Graphs
The animation can be paused before the two graphs go off the screen by pressing . Notice the highlighted PAUSE at the bottom right of the screen below. You can restart the graphs by pressing , or press to regraph starting at t = 0.
12.1.4 What feature of this graph shows the times when the particle appears to change direction? A Different Model of the Particle's Motion Parametric equations can be used to make a different model of the same particle motion. The functions below represent the same motion shown earlier, but time is shown on the xaxis and the particle's position is represented by the yvalues. Set the graphing style to thick.
The particle's instantaneous velocity can be displayed along with its position. Defining new parametric equations where the xvalues represent time and the yvalues represent the particle's instantaneous velocity (the derivative of the function in yt1) can do this.
12.1.5 How do these graphs show when the particle is moving left, moving right, and at rest? 

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