Drag coefficient of vertically moving popcorns

Abstract

To take the students attention in physics lectures is always a challenge. The projectile motion is not an exception. Then, study of popcorn motion can be a way to introduce and motivate the students in this subject. In this work, the popcorn flight, caused by the popping process was recorded by a cellular phone and analyzed frame by frame. Then, the drag coefficient (CD) of vertically moving popcorns is determined and its dependency with the vertical velocity (vy) and with the Reynolds number (Re) is explored. Our results show that CD increases exponentially when vy decreases. Also, CD shows higher uncertainties when the popcorn is close to its maximum vertical trajectory. The dependency of CD with Re shows that the popcorn flights are governed, mainly, by a laminar flow motion (Re < 2000).