Objective
The purpose of this experiment was to examine the impact of two hockey pucks in an inelastic collision and to confirm that momentum and energy are almost entirely conserved, allowing for the inherent errors involved in the observation process. The law of conservation of energy states that during a collision, energy can neither be gained nor lost, but can be transferred or transformed. During an elastic collision, the energy and momentum is transferred from one object to another. Unlike in an inelastic collision (such as the kind seen in the previous laboratory experiment), we expect kinetic energy in an elastic collision to be conserved.
Questions
Question 1
(a) Linear momentum is not conserved in situations where there is a net external force acting on the system. This means that the sum of the forces on the system from the outside is not zero and that an “unbalanced” force is acting on the system.
(b) Some systematic sources of error that would likely cause linear momentum not to be entirely conserved include the force of friction. In addition, the pucks themselves may have been spinning about their own axes, and some of the force of the collision may have been transferred to the pucks' spin rather than to their motion along the plane.
(c) Based on the systematic errors I would expect initial momentum of the system to be greater than the final momentum (pi > pf).
(d) My prediction is true for the results.
(e) An experimenter might find the opposite result to be true (that pf > pi) if human errors are made. These include errors in the measurement of the momentum vectors and errors due to the imprecision of the measuring tools.
(f) While making only two measurements of momentum before the collision and only two measurements after the collision might improve the fractional error, it would not create as precise a picture of the momentum vector. Having multiple measurements taken 0.1 seconds apart allows us to measure the momentum with greater precision.
Question 2
(a) KEi = 0.261 kg m/s; KEf = 0.195 kg m/s
(b) ΔKE = 0.261 – 0.195 = 0.066 kg m/s
(c) PFE = 25% This percent fractional error is rather high, but in light of the fact that perfect conservation of momentum is a theoretical expectation and not a practical one, it is acceptable for this experiment.
Discussion
Truly elastic collisions exist only in the theoretical realm of physics. In practice, no collision can occur without the dispersal of kinetic energy. Our experiment failed to take into account significant physical factors, such as friction, that most likely affected the outcome of the collision. Although the experiment approximated a totally elastic collision within a reasonable margin of error, it is impossible to obtain results that confirm conservation of momentum with 100 percent accuracy.
Error Analysis
There are always sources of error present in laboratory experiments. In this lab, there were at least two possible sources of error that were human in origin. The first human error could have resulted from the imprecision of the measurement tools used to determine the momentum vectors of the pucks. The second human error may have occurred when joining the vectors together to produce the resultant vector.
Conclusion
The experiment was deemed a success and yielded results that confirm the conservation of momentum in two dimensions. The disparity between the theoretical and experimental values was within experimental limits.
