INVESTIGATIONS OF PHYSICS LECTURE DEMONSTRATIONS: TWO-BULLET PROBLEM AND PARAMETRIC EXCITATION OF U-TUBE OSCILLATIONS
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Authors
Steiner, Hannah S.
Subjects
physics
demonstrations
two bullet
U-tube
non-linear systems
demonstrations
two bullet
U-tube
non-linear systems
Advisors
Larraza, Andres
Denardo, Bruce C.
Date of Issue
2020-06
Date
Publisher
Monterey, CA; Naval Postgraduate School
Language
Abstract
Lecture demonstrations strongly convey physics concepts and theories. In addition, realistic issues arise that are often not in a model theory. Investigations of lecture demonstrations are published in scholarly journals and are Navy-relevant due to use in classrooms. We investigate two lecture demonstrations. One is the “two-bullet problem,” where a body is released from rest at a height, and another is simultaneously projected at the same height. In a vacuum, it is well known that both strike the floor simultaneously. For the common case of quadratic drag, however, the dropped body is predicted to strike the floor first. We develop a classroom demonstration that clearly exhibits the effect, but the result is suspect because numerical simulations show that the time difference is too small to be clearly discernible. Arguments to resolve the inconsistency are made. In the other demonstration, we describe the first successful parametric excitation of oscillations of the liquid in a U-tube. This is difficult to achieve due to a large drive amplitude threshold. Only a nonlinearity can limit parametric growth and thus lead to steady-state motion, but the observed motion is in the Hooke’s law regime, and the dissipation is very nearly linear. Possible reasons for the steady-state motion are discussed. Also surprising is that the free decay transitions from one damping parameter to a greater one at small amplitudes. We propose a possible reason for this behavior.
Type
Thesis
Description
Series/Report No
Department
Physics (PH)
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Distribution Statement
Approved for public release. distribution is unlimited
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.