Earth's gravity pulls all objects toward its center, and near the Earth's surface. Objects in free fall accelerate at 9.8 m/s2 vertically downward, provided air resistance is negligible. This value of acceleration is often referred to as "g". There are many ways to measure this rate of acceleration, and most require a timing device. Typically, stopwatches are the least expensive technology, so these are commonly available in high school science classrooms. With the recent addition of movie cameras on cell phones and digital cameras, another timing tool is available at moderate cost (free if the school policy allows students to use their personal cell phones during class time). The following set of experiments provide four ways to calculate g using (1) a 10-meter (25-yard) tape measure, (2) a brightly colored ball, (3) a stop watch, (4) a digital camera with movie mode, (5) a tripod, and (6) free software called MovieTracker (http://www.lawrencehallofscience.org/gss/rev/ip/index.html).