**Task**

Your task is to explore how characteristics of the vector affect the
movement of the car as you use the vector to "drive" the car around
without crashing into the walls. Adjust the vector by dragging either
endpoint, or move it by dragging the dot on the vector. How do your
adjustments of the vector affect the numbers at the bottom of the
screen? Now start the car by clicking on the "Start Car" button. Try to
drive the car around the box without crashing. As you do this, consider
the following questions:

- How do the numbers for direction and magnitude correspond to the appearance of the vector?
- How do those numbers correspond to the movement of the car?
- What happens when you move the vector into a new position using its midpoint?

How can you make the car stop? What are the values of the vector's
characteristics when this happens? What might this situation be called?

Now
click the box to "Show Cyclone." Your goal is to chase after and
attempt to "catch" the cyclone without crashing into the walls. Try to
catch the cyclone by controlling the car's movement with the vector.
Then reset the game and try to catch the cyclone using only the sliders
at the bottom of the screen, without directly manipulating the vector.

**Discussion**

Vectors are used in numerous applications and are very
important in the sciences and engineering. Vectors extend students'
thinking about rates of change and should receive concentrated attention
in schools. They are useful in representing various situations; in this
example a vector is used to represent the velocity and direction of a
moving object. Through experiences with the applet, students should make
a number of observations about vectors and their components.

First,
they should see that vectors have two components—magnitude and
direction. In this case, the magnitude of the vector controls the speed
of the car and the direction of the vector controls the direction of the
car. Vectors can be represented graphically, in the form of an arrow,
or numerically, as length and angle measurements. By dynamically linking
the graphical and numerical representations, this applet enhances
students' ability to connect algebra and geometry.

Students
should further come to see that the position of the vector on the screen
is of no importance; dragging it around by its midpoint does not change
the speed or direction of the car. The relevant features of a vector
are its length (magnitude) and direction (angle).

Finally,
students might observe that adjusting the length of the vector to 0
causes the car to be stationary. They may note that this state could be
called the identity element for vector addition. They could be
challenged to think about whether the identity is unique, since if the
length of the vector is 0, its angle has no effect.

**Take Time to Reflect**

- Why might you wish to begin the study of vectors with a vector that
represents velocity rather than one that represents change in position?
- What are some of the
advantages of using a dynamic representation? Are there disadvantages?
- Contrast the instructionally
appropriate ways in which this applet might be used with some inappropriate
ways. What might a teacher do to focus students' attention on the mathematics
embedded in the situation?

**Acknowledgments **

Special thanks to Brian Keller for timely work in creating the
vector applets and to Gerd Kortemeyer for assistance in developing the
activity.