The Arch of a Light Beam
Yiqiao (Rachel) Yang
Award: Top 100
School: winston churchill high school
Teacher: jennifer czaplicki
Category: Contrived
Photo #21461
The Arch of a Light Beam
The image features the projectile motion of a flashlight. First, to capture the entire trajectory in one image, I set my camera's shutter speed to 5 seconds. Then, as soon as I pressed the shutter button, I ran up to the edge of the frame to launch my flashlight.
The trajectory of the flashlight was a vertical parabola opening down. This was because the flashlight experienced no horizontal acceleration but a constant downward vertical acceleration of about g=9.81 m/s^2 due to the gravitational force on Earth. As the flashlight moved upward, its vertical velocity decreased at the constant rate of g until it became zero; then, as it fell, its vertical velocity increased in magnitude at the same rate of g, until the flashlight returned to its original height and had the same vertical speed as the initial. Throughout the flight, the horizontal velocity remained constant.
Obviously, because the image wasn't taken in a vacuum, there was a resistive force from air exerted on the flashlight throughout the trajectory. Nonetheless, that effect must've been negligible, since the captured trajectory still resembled almost a perfect parabola. At the same time, because my launch wasn't perfect, it applied a torque to the flashlight thus causing the direction of the light beam to rotate away from the direction of the camera as it moved, which is why the light faints in the later portion of the flight. Nevertheless, the light arch was an overall accurate depiction of projectile motion.
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