From the bar graph, we see that the potential energy in general agrees with the case above, i.e. it increases up to the maximum height of the particle and decreases from that point onwards. Kinetic energy, however, behaves significantly differently than expected. Instead of decreasing from the beginning to the maximum height and then increasing, the kinetic energy appears to fluctuate somewhat randomly. This can be better understood by treating the experiment as a closed system, where energy (but not mass) can leave the system and enter the surrounding environment. As the projectile moves through the air, it collides with air particles, transmitting some of its energy to these particles in the form of friction, heat and sound, thus losing energy in the process. We would therefore expect the sum of potential energy and kinetic energy to decrease over time as the projectile loses energy to its surroundings. However, from the data in the paper, this also does not appear to be the case. This discrepancy can be explained by including experimental uncertainty, where errors in our measurements can lead to unjustified conclusions. To reduce the sources of these errors, the experiment should be run several times under ideal conditions, averaging the results and calculating the resulting average energies. In summary, the law of conservation of energy is indeed true. In