ERIC Number: EJ1059714
Record Type: Journal
Publication Date: 2015-May
Abstractor: As Provided
Reference Count: 13
Half Empty or Half Full?
Rohr, Tyler; Rohr, Jim
Physics Teacher, v53 n5 p275-278 May 2015
Previously appearing in this journal were photographs of a physics apparatus, developed circa 1880, that was believed to be used to demonstrate the "Bernoulli effect." Drawings of these photographs appear here and show that when there is no flow, the water level h[subscript PT2] in the piezometer tube at location (2) is at the same level as in the head tank [Fig. 1(a)], but drops to about half the previous level when there is flow [Fig. 1(b)]. We are in agreement that the drop in static pressure at the base of the piezometer tube is associated with the Bernoulli effect, i.e., the qualitative behavior of the lowering of fluid pressure in regions where the flow velocity is increased. However, we also believe that the height of water in the piezometer tube has an equally rich story, a story that better unfolds by addressing the following questions: What does the presence of water in the piezometer tube indicate? What water level would the Bernoulli equation, which is derived for flows where viscous friction is negligible, predict? Qualitatively, how do the exit velocities and piezometer tube water levels vary for inviscid (no friction) and viscous (friction) flows, and the following exit geometries: straight [Fig. 1(c[subscript i])], diverging [Fig. 1(c[subscript ii])], and converging [Fig. 1(c[subscript iii])]?
Descriptors: Science Instruction, Physics, Scientific Principles, Scientific Concepts, Laboratory Equipment, Water, Equations (Mathematics), Motion
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Publication Type: Journal Articles; Reports - Descriptive
Education Level: N/A
Authoring Institution: N/A