Determination of Restitution Coefficients for Collision Using 3-Points Moveable Sensor Configuration

The collision experiment apparatuses that have currently developed can not able to assist students in understanding relation of physical parameters on the experiment that involves a collision restitution coefficient. This paper describes the development of the collision experiment apparatus for restitution coefficient determination based on free fall motion experiment. The system uses three couples of infra-red (IR) LEDs CQY99 as transmitter and photodiode sensors SFH 203FA as receiver while the data recording is driven by an SMD based Arduino Uno with an ATmega328 microcontroller. The sensors were mounted on a vertical transparent acrylic pipe in diameter of 100 mm, thickness of 5 mm and height of 1200 mm. The measuring used objects are spherical masses with varied diameter and type. The apparatus is installed on a 3-points configuration where the sensors are placed on three positions; sensor 1 is placed on the top, sensor 2 is in the middle, and sensor 3 at the bottom of the acrylic pipe. Sensor 1 and 2 can be adjusted according to the desired measuring distance. The work system of this apparatus is divided into three parts, that is: determining the acceleration of falling objects, application of the restitution coefficient, and helping students explore physical parameters related to the coefficient of restitution. The electronic circuit is designed with in two functions so that apparatus can calculate the period when the objects fall (t 1 ) and bounce (t 2 ). The surface of the apparatus is optimized to minimize air friction, so that the falling objects acceleration is equivalent to the Earth's gravity ( $\mathbf{g}=9.8\ \mathbf{m}/\mathbf{s}^{2}$ ). To obtain the collision restitution coefficients (e) over the calculation, the bouncing surfaces were varied. The results of the collision experiment have shown the persistence of the collision restitution coefficient parameter, with the results of $\mathbf{g}=9.79\pm 0.0032\ \mathbf{m}/\mathbf{s}^{2}, \mathbf{u} , and as shown in the results, the value of e of a freely falling object is 0 < e < 1. Based on this result, the apparatus can be used as collision experiment tool at schools to help students in understanding the concept of free fall and collision restitution coefficients.