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Abstract A positive cloud‐to‐ground (+CG) lightning flash containing a single stroke with a peak current of approximately +310 kA followed by a long continuing current triggered seven upward lightning flashes from tall structures. The flashes were observed on 4 June 2016 at the Tall Object Lightning Observatory in Guangzhou, Guangdong Province, China. The optical and electric field characteristics of these flashes were analyzed using synchronized two‐station data from two high‐speed video cameras, one total‐sky lightning channel imager, two lightning channel imagers, and two sets of slow and fast electric field measuring systems. Three upward flashes were initiated sequentially in the field of view of high‐speed video cameras. One of them was initiated approximately 0.35 ms after the return stroke of +CG flash from the Canton Tower, the tallest structure within a 12‐km radius of the +CG flash, while the other two upward flashes were initiated from two other, more distant tall objects, approximately 18 ms after the +CG flash stroke. The initiation of the latter two upward flashes could be caused by the combined effect of the return stroke of +CG flash, its associated continuing current, and K process in the cloud. Each of these three upward flashes contained multiple downward leader/upward return stroke sequences, with the first leader/return stroke sequence of the second and third flashes occurring only after the completion of the last leader/return stroke sequence of the preceding flash. The total number of strokes in the three upward flashes was 13, and they occurred over approximately 1.5 s.
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Impetus-Force-Like Drawings May Be Less Common Than You Think
Perhaps the most commonly cited student idea about forces in the literature is the notion of an impetus force, defined as the “belief that there is a force inside a moving object that keeps it going and causes it to have some speed,” that can then “fade away as the object moves along.” According to the literature, even after physics instruction students use impetus force reasoning to argue that forces are necessary to sustain motion or that motion implies force. For example, many students drew an upward arrow to indicate a force on a coin that was moving upward after being tossed. The coin was halfway between the point of its release and its turnaround point. Interviews with students in the course indicate that the arrow was meant to indicate “the ‘force of the throw,’ the ‘upward original force,’” and so on. Clement interprets these results to mean that students “believe that continuing motion implies the presence of a continuing force in the same direction, as a necessary cause of the motion.”
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- PAR ID:
- 10357657
- Date Published:
- Journal Name:
- The Physics Teacher
- Volume:
- 60
- Issue:
- 4
- ISSN:
- 0031-921X
- Page Range / eLocation ID:
- 254 to 257
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1119/5.0027858
