[Wait until the applet loads completely {you will see a message down in the status bar saying it is "running"} before pressing PLAY.]
A ball moves across the screen with constant velocity.
If we wanted to figure out the speed of the ball .. we could measure the distance the ball travels and measure the time, and divide the distance by the time. How can we measure the distance? Well, right now, it is easy, because the position of the ball is shown in the animation! Try pausing the animation, and then using the mouse, click in the animation at the center of the ball - you see some yellow coordinates pop up in the bottom left corner of the animation window. That is the X and Y coordinates of the point where you click down the mouse (notice the x coordinate of the center of the ball is the same as the postion label!) So, if we pause, measure, step forward a known amount of time, and then measure again, we could calculate the velocity .. you should find it to be 2 m/sec!
These java applets are amazing, but every once in a while they "pause" on their own .. just hit RESET and then PLAY again.
When you load a physlet page, always make sure you wait until the "applet" fully loads before trying to run it (if you run it locally, they load very fast, but over the web, they may take longer to load). You should see an "APPLET RUNNING" line in the lower left status bar of your browser when the applet is ready to run. Some applets start automatically, for others, you must press play to get them to start.
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