Autoren:Pürmayr, Josef E.; Wolny, Brigitte; Hopf, Martin
Abstrakt:Constant acceleration can easily be studied using gravitational force, such as free fall, simplified by an inclined plane. For two dimensional motions, observation of a thrown object expands the idea of one dimensional acceleration (gravity) by a constant speed in a (perpendicular) direction. Gravity, however, is a concept which is not only hard to understand, but also one, which is highly influenced by pupils’ misconceptions (Stadler, 1996). Furthermore, gravitational effects act invisibly and are not a subject to control. These are two difficulties about learning, coming with gravity. Alongside these two difficulties, preconceptions about force, acceleration and velocity have to be taken into account. Shifting the movement to a tabletop-plane and reducing friction lock out gravitational effects. A linear air track or fan driven cart (Morse, 1994) can be used to create a suitable setting in one dimension. However, one dimensional motion leads to other difficulties such as the transfer to two dimensions.One way to overcome those difficulties is to use two dimensions from the start. The idea of a constant acceleration (gravitational force) is substituted by a modifiable air current, driven by a fan in any direction parallel to the tabletop-plane. This model allows exploring accelerated motion in a two dimensional setting, without activation of students’ preconceptions about gravity, by providing a simple and low cost hands-on-experiment. We designed a hover puck, driven by two DC-motors with fans (one vertically and one horizontally), provided with power of cellphone batteries. The hover puck reduces friction to a minimum, allowing to create a setting in which a constant accelerated motion can be portrayed. Additionally, modifications such as a negative initial velocity and an initial movement in any direction can easily be added, offering a broad range for exploring two-dimensional, accelerated motion.One core point of designing the hover puck was to realize it as a low cost experiment. Most of the components are household objects and the assembling can easily be done by students at home or at school. The total cost of the hover puck sums up to about 15€, if propellers and DC-motors have to be bought. Costs and effort can be reduced drastically, if a 3D-printer is available. The setup for motors and batteries can be printed by a data-file provided, which is planned to be published on the Website of the Austrian Educational Competence Centre Physics. Batteries are not included in the costs, since old cellphone-batteries are sufficient for powering the hover puck. They usually can be charged using an universal charger.