Earth's gravity causes all objects (with mass) to accelerate towards its center with a fixed rate which is anything between 9.78 and 9.83 m/s2 depending on the altitude. Roughly we say that the rate of acceleration is 9.8 m/s2. And this applies to all objects regardless of the mass. Tim Gibbon made a device to measure the acceleration. A ball begins to fall. As it falls it goes through a beam of light. When the beam is cut (sensed by an LDR on the opposite side), the microcontroller starts counting the time. At the bottom end there is an MS24P/10 vibration sensor. When the ball reaches the end, the microcontroller stops counting. Then it does some math and estimates the acceleration rate. The result is shown on a converted 10mA FSD English Electric Ammeter with a 570 Ohm resistor. The instrument is calibrated for Earth, Mars and Jupiter... I'd like to see the results on Jupiter :D