Light Propulsion
Robert Page
Award: Top 100
School: leigh high school
Teacher: marita beard
Category: Contrived
Photo #21257
Light Propulsion
This photo is of a rotating drone propeller with water sprayed onto it illuminated under green LEDs. Due to the high velocity of the propeller (approx 3000-5000 RPM), parts of the propeller on the lower half of the image appear blurred. This is due to the rolling shutter effect which explains how certain camera sensors read images line by line, meaning that the propeller can be in another location by the time the camera has moved onto the next line provided its velocity is sufficient.
Around the center of the propeller, there are streaks of lights directed perpendicular to the axis of rotation of the propeller forming a circular pattern. These streaks are the byproducts of the water sprayed onto the propellers prior to arming the motor. As the propeller accelerates to idle, the water "left behind" because the water is located a distance R away from the axis of rotation meaning it has a rotational mass inertia that resists the acceleration of the propeller.
The speed in which some of the water is accelerated from the propeller causes the water to collect millions of tiny air bubbles making some of the streaks appear white due to the amount of reflection and refraction that occurs in these particles of water.
The rest of the water droplets that did have sufficient surface tension to form streaks also underwent centripetal acceleration which is shown by the thousands of tiny droplets ejected from the propeller in the edges of the frame.
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