Procedure

    1. Push the CALIBRATE button in order for the applet to work with the clock speed of your machine. You only need to do this once.
    2. Select "Moon" from the planet selector box underneath the stopwatch.
    3. Pushing the DROP button will cause to ball to fall.
    4. See how long it takes for the ball to drop 6 meters. Do this a few times to make sure that your machine registers the same time (to within 0.01 second) each time. The correct time is 2.71 seconds.
    5. There is a red and green marker available on the ruler. Their default positions are at 0 and 6 meters. Move your mouse to the 1m mark on the ruler and click it. That will position the green marker there (note: you can grab the marker with the mouse and move it as well). Now go to the bottom and grab the red marker and move it to 3m.
    6. Push the DROP button again and the stopwatch will only time between 1 and 3 meters. Record this time.
    7. Now move the green marker to 0m and the red marker to 2m and repeat and record the time. Do the same for intervals of 2 to 4m, 3 - 5 m and 4--6m.
    8. The average velocity is determined by the time it takes for the ball to go a given distance. Compute the average velocity for each of the two meter distance units that you have previously defined. Why is the average velocity increasing as the ball falls?
    9. Now select either Earth or Mars and time how long it takes the ball to fall the full 6 meters on the other two planets.
    10. Using the difference in the freefall times, compute the difference in surface gravity between the Earth, Moon and Mars