Galileo timed a ball as it rolled down a plank.He used a dripping water clock.The volume of the drips was a measure of time.He measured the time for equal distances.The ball accelerated as it rolled down the slope.
Galileo used an inclined plane rather than free fall because free fall is too quick, and he had no accurate method to measure time. An inclined plane reduces the acceleration so the motion can be timed.For an object of mass m on a slope at angle θ to the horizontal, the weight mg can be resolved into two components:parallel to the slope: mg sinθ
perpendicular to the slope: mg cosθ The perpendicular component is balanced by the normal reaction. Ignoring friction, the parallel component gives the object its acceleration:a = g sinθ A shallow slope gives a small acceleration. As θ increases towards 90°, the acceleration approaches g, the free fall value.Galileo found that the distance travelled from rest was proportional to the time squared (s = ½at2). This showed that the ball moved with constant acceleration, and he argued that falling objects do the same.
Galileo used an inclined plane rather than free fall because free fall is too quick, and he had no accurate method to measure time. An inclined plane reduces the acceleration so the motion can be timed.For an object of mass m on a slope at angle θ to the horizontal, the weight mg can be resolved into two components:perpendicular to the slope: mg cosθ