Conservation of Energy Lab – PHY 141 and PHY 161
Introduction: Measure the speed of a glider on an air track, pulled by a hanging weight
which is connected to the glider by a light string over a pulley of negligible mass. If the
hanging weight drops by a distance h, conservation of energy predicts the final velocity of
the glider: vth = SQRT[2MHgh/(MH+MC)].
1. Is the (final) velocity constant?
2. Is the average velocity in agreement with the theoretical prediction?
3. Is energy conserved?
Data: Table 1 (vary h) and Graph 1 (v2 vs. 2MHh/(MH+MC)).
Table 2 (vary MH) and Graph 2 (v2 vs. 2MHh/(MH+MC)).
Analysis:
Table 1 − Variation of h
Show MH and MC, and the range of h values used. Also show Max%Unc.
1. Pick the worst-resulting h value, the one with the largest %Diff(vth, vavg). Show h,
%var(v), vth, vavg, %Diff(vth, vavg), and the ratio Kf/Pi. For this case, was the measured
velocity constant? Was the theoretical prediction correct? Was energy conserved?
2. Show the experimental and theoretical slopes for the graph, and their percent
difference. Do they agree, within the experimental errors?
3. Generally speaking, was the measured velocity constant? Generally speaking, was the
theoretical prediction for v close to the average measured velocity? Generally
speaking, was energy conserved?
Table 2 − Variation of MH
Show h and MC, and the range of MH values used. Also show Max%Unc.
1. Pick the worst-resulting MH value, the one with the largest %Diff(vth, vavg). Show MH,
%var(v), vth, vavg, %Diff(vth, vavg), and the ratio Kf/Pi. For this case, was the measured
velocity constant? Was the theoretical prediction correct? Was energy conserved?
2. Show the experimental and theoretical slopes for the graph, and their percent
difference. Do they agree, within the experimental errors?
3. Generally speaking, was the measured velocity constant? Generally speaking, was the
theoretical prediction for v close to the average measured velocity? Generally
speaking, was energy conserved?
Conclusion: Provide final answers to the questions presented in the Introduction. It is not
necessary to quote again the numbers from the Analysis. However, do provide your best
explanation for the lack of agreement between theory and experiment, if any such
disagreement exists.
Additional questions: Answer questions 1-4 from the Lab Instructions (pdf file).