Creating Sliders in Geometer’s Sketchpad

“What’s a slider?”

A slider is a tool you can use to change the value of something very easily. A typical slider has a handle you can drag up and down (or left and right) to raise or lower the value of something, sort of like a volume control.

“How do you make one in Geometer’s Sketchpad?”

Since Sketchpad doesn’t come with a slider tool, we’ve got to make one from scratch. There are a few ways we could do this, and I’ll outline one of the simplest methods step by step.

  1. First, we’ve got to set up a coordinate system. Go to the “Graph” menu and select “Grid Form” and then “Square Grid”.

You should get the following coordinate system:

  1. Now, select the “Point Tool” button and create a point anywhere you want.

  1. By default, the point will be selected after you have made it. (If you managed to unselect it, then just click on the “Selection Arrow Tool” button and select it again.) With the point selected, select the “Transform” menu and click “Translate…”.

When you do this, the following window will come up:

Our goal here is to create a new point directly above the one we first made. By default, polar coordinates are given, b ut just to be safe, let’s switch to rectangular coordinates and set where our new point should be.

In the “Translation Vector” section, select “Rectangular”.

Let’s set the new point to be 0.0 cm across and 1.0 cm above our original point.

Hit, the “Translate” button, and you’ll now have two points.

  1. The next step is to create a strictly vertical line. To do this, click and hold the “Straightedge Tool” button.

Drag and select the last option, which has two arrowheads. This is for creating a line that extends infinitely in both directions.

Now, bring your mouse cursor over the first point. (It will turn blue when you’re over it.)

Click and drag the cursor up until you’re over the second point. (It will also turn blue.) And then let go.

You should now have a line passing through both points.

  1. Select the “Point Tool” button. We’re going to create another point, but this time, we’ll be putting it on the line we just made. (The line will turn blue when the point is over it.)

Click and let go.

  1. Select the “Selection Arrow Tool” and click anywhere empty to deselect everything. Now, select the line and the translate point we made.

Select the “Display Menu” and click “Hide Objects”. (Or just hit Ctrl-H.)

The point and line will disappear, leaving just two points.

  1. Now, we’re going to create a line segment connecting these two points. Simply select both points, go to the “Construct” menu and select “Segment”. (Or, just click Ctrl-L.)

You should get a simple line segment.

  1. Deselect everything and then select just the two points. Then, go to the “Measure” menu, and select “Ordinate (y)”.

You’ll now have the y-coordinates for the two points.

But what we want is the difference in their y-positions. To get this, we’ll need to create a calculation. Go to the “Measure” menu and select “Calculate…”.

When you do this, you’ll get a “New Calculation” window.

What we want is to calculate yA – yB. To do this, first click on the “yA = (some number)” box in your Sketchpad window. Then type the “minus” key. And finally hit the “yB = (some number)” box. Your equation should look like something this:

Hit OK. Your equation should now appear.

  1. Ok, now we’ve just got to do a little clean up and our slider will be ready. First, deselect everything. Then, double-click on the letter B. The following window will come up.

Uncheck “Show Label” and hit OK. Now do the same thing for A. Next, select only the “yA = (some number)” box, the “yB = (some number)” box, and the bottom point.

Hide them. (Select the “Display” menu and then “Hide Objects”, or hit Ctrl-H.)

Your display should now look like this.

Finally, right-click on the “yA-yB = (some number)” box, and select “Properties…”.

Select the “Value” tab and in the “Display With” section, select “No Name”.

Hit OK. And now, simply move the number next to the slider and you’re done.

To test out the slider, click on the point and drag it. You’ll see the number change as the slider moves. (You can even get negatives – try it!)