Question

A frame-by-frame analysis of a slow-motion video shows that a hovering dragonfly takes 7 frames to complete one wing beat. If the video is shot at 240 frames per second, (a) what is the period of the wing beat, and (b) how many wing beats does the dragonfly perform per second?

A) 7 seconds
B) 1/7 seconds
C) 30 seconds
D) 240 seconds

Answer 1

The period of the dragonfly's wing beat is approximately 1/7 seconds (0.02917 seconds), and the dragonfly performs 7 wing beats per second when a video is shot at 240 frames per second with 7 frames per wing beat.

Explanation:

To find the period of the dragonfly's wing beat, we divide the number of frames per wing beat by the frame rate of the video. If it takes 7 frames to complete one wing beat and the video is shot at 240 frames per second, calculating the period (T) is straightforward:

T = number of frames for one wing beat / frame rate
T = 7 frames / 240 frames per second
T = 0.02917 seconds per wing beat

In this case, the closest answer from the options provided would be B) 1/7 seconds, because 0.02917 seconds is approximately equal to 1/7 seconds.

To find the number of wing beats per second, which is the frequency (f), we simply take the reciprocal of the period:

f = 1 / T
f = 1 / (1/7) beats per second
f = 7 beats per second.

Therefore, we can conclude that the correct answer is B) 1/7 seconds for the period, and the dragonfly performs 7 wing beats per second.