.To describe falling objects, it’s necessary to make precise measurements of two variables: distance and time. Distance was easily measured by Galileo and his contem- poraries using rulers, but their timepieces were not precise enough to measure the brief times it took objects to fall straight down. While previous workers had simply observed the behavior of falling objects, Galileo constructed a special apparatus designed purely to measure acceleration (see Figure 2-8). He slowed down the time of fall by rolling large balls down an inclined plane crafted of brass and hard wood, and measured th