This research aimed to design the simple apparatus to improve students' conceptual understanding in projectile motion. The projectile tube experiment was a simple apparatus that consisted of a one-meter PVC tube, a 1200-watt hair dryer, a hard sheet of paper, and a ping pong ball. The participants were 30 grade 10 students who were selected by non-random sampling in the second semester of the academic year 2018. The research tools consisted of learning lesson plans and a multiple-choice learning achievement test. The class activity was conducted by using the Interactive Lecture Demonstrations (ILDs) method with Tracker Video Analysis. The results showed that the experiment set worked perfectly and could be used for learning the projectile concept. The students' achievement score was significantly increased at a statistical level of .05 and the average of students' normalized gain was in a medium gain regime.