I have performed an experiment testing how mechanical energy is conserved. I conducted this experiment by first creating a ramp. I gathered data by first calculating the gravitational potential energy of a marble on various points on the ramp (depending on height). Next I rolled the ball down the ramp, and when it hit the ground I started a stopwatch and timed how long it took to travel 1.17 m on a flat plane. I used this to find the average velocity. The mass of the marble is .0284 kg, so with all this data I was able to calculate the final kinetic energy (neglecting friction). Here is the data for four trials where each trial changes depending on the initial height the marble started at on the ramp: Height (m): 0.05 0.06 0.07 0.08 Parallel component of weight (N): .13 .13 .13 .13 Work (J): .009 .014 .020 .023 Initial potential energy (J): .014 .017 .019 .022 Final kinetic energy (J): .002 .003 .004 .006 I am confused about the last portion of the data. If the marble started with, say, .014 J of potential energy, why does it only have .002 J by the end of the 1.17 m it rolls on the ground? Does it lose .012 J of energy due to friction, or are my calculations incorrect?