The next type of transformation we shall look at is called a reflection. Click the "On/Off" button on the applet to start it.
As before, the brown circle is the object and the blue one the image. You can drag the object (brown) with the mouse. Watch what happens to the image.
What do you think the black line represents?
The black line is called the mirror line. We can move the mirror to other positions. If you click on the "Mode" button. Two tiny red dots will appear on the mirror line. Remember that you only need two points to determine the position of a line. By dragging the red dots you can move the mirror line as you please. (If you decide to move the object you can click the "Mode" button once again and then drag the object with the mouse). Here are a few things for you to investigate.
If I told you that the object and the image were in the same place, where would they be? If a point is on the mirror line, its image is at the same location. We call such points fixed points.
If the mirror line is vertical, what can you say about the line that runs through the object and image?
If the mirror line is horizontal, what can you say about the line that runs through the object and image?
The line that runs through the object and image is always perpendicular to the mirror line. How is the distance of the image from the mirror line related to the distance of the object from the mirror line? The mirror line is the perpendicular bisector of the line segment from the object to the image.
e-mail: C. Mawata