In this example we will use pendulum motion to actually measure the acceleration of gravity on a different planet. an astronaut on the surface of mars measures the frequency of oscillation of a simple pendulum consisting of a ball on the end of a string. he finds that the pendulum oscillates with a period of 1.5 s. but the acceleration due to gravity on mars is less than that on earth, gmars=0.38gearth. later, during a journey to another planet, the astronaut finds that his simple pendulum oscillates with a period of 0.92 s. what planet is he now on? solutionset up each planet has a different value of the gravitational acceleration g near its surface. the astronaut can measure g at his location, and from this he can determine what planet he's on. first we use the information about mars to find the length l of the string that the astronaut is swinging. then we use that length to find the acceleration due to gravity on the unknown planet.