Should we teach free-body diagrams before or after Newton’s Laws?

There are two interesting lesson sequences for teaching force and motion in high-school physics. These are teaching free-body diagrams before Newton’s laws (FbN) and teaching Newton’s laws before free-body diagrams (NbF). Both sequences were found in physics textbooks. Different authors adopted the sequence that they believe it would affect student understanding better. However, some physics experts did not agree with this. It is therefore interesting to know if we should teach with the FbN or NbF sequence. This motivates us to study the effect of such lesson sequences on student understanding of force and motion. The sample group was grade-10 students from two physics courses in 2020. One course was taught with the FbN sequence (29 students) and the other with the NbF sequence (34 students). Their understanding was evaluated by using an assessment test which consisted of three parts including (1) Newtonian concept, (2) problem solving, and (3) free-body diagrams. The result shows that for the Newtonian concept part, the average scores are 11% for the FbN and 13% for the NbF sequence. The average scores of the problem-solving part are 13% and 9% and those of the free-body diagram part are 41% and 48% for the FbN and NbF sequences, respectively. The scores of all parts between the two sequences were not significantly different. In addition, student difficulties found in all parts were similar. However, a larger number of students who could provide the equation of motion (F = ma) in the problem-solving part was found in the FbN sequence. We might conclude that teaching free-body diagrams before or after Newton’s laws did not affect student understanding in the topic of force and motion. Detail of student difficulties in both sequences will be further discussed.

PEMANFAATAN KICK FOOT SENSOR UNTUK MEKANISME BUKA TUTUP BAGASI KENDARAAN

Along with its development, car manufacturers are increasingly improving safety and security features in each of their products. Currently, this element of safety and security has become an important target in the development of the existence of various features that exist in a vehicle. In this study, the power back door feature is implemented by using the kick foot sensor as input data to open and close the trunk of the vehicle through the actuator. This feature uses a foot sensor so you don't have to press any buttons, just point your foot under the rear bumper and the sensor will automatically read and open the trunk door. This feature is very helpful for passengers who want to put their luggage in the trunk but have both hands to carry items such as bags or plastic shopping bags. There are several stages carried out in this research. In the first stage, the specification of the required actuator motor, including force and torque, is carried out by analyzing the free body diagram to be able to open and close the trunk. In the second stage, the trunk door is tested when the condition is open and close. From the test results, the average time to open the trunk is 11.79 seconds, while the average time to close the trunk is 11.56 seconds. The time obtained is faster than the initial design target set, which is 15 seconds both when opening and closing the trunk. While the sensitivity of the motion sensor can range from 20 mm to 400 mm when the foot is directly under the sensor.

Method for Estimating Speed of the Out-of-Control Tractor-Semitrailer on Downhill Grades

Speed estimation for the out-of-control truck on a downhill grade is essential for passive safety features like truck escape ramps to promote traffic safety. This paper presents a method for estimating the speed of out-of-control trucks based on Newton’s Laws of Motion. First of all, we analyze gravity effort, aerodynamics, and rolling resistance through a free body diagram of an out-of-control truck on a downhill grade. Further, we select the speed as the dependent variable, with the following road and vehicle characteristics as independent variables: road surface type, grade, grade length, truck size, truck weight, and tire type. Finally, we estimate the speed and acceleration according to Newton’s Laws of Motion. The results show that the factors that significantly affect the out-of-control truck’s speed include tire type, road surface coefficient, grade, and grade length. TruckMaker simulation results demonstrate that the model is valid at a 99% confidence level.

Modelado y simulación del péndulo de base móvil

This article describes the simulation and control of a mobile base pendulum (PBM), which consists of a mechanism with two wheels and a vertical cylindrical rod, which can rotate freely on its own axis, then the mobile must move to compensate for the angular displacement of the pendulum. The objective is to develop a mathematical model to simulate the dynamic behavior of the mechanism and thereby develop a Proportional, Integral and Derivative (PID) controller, optimal that manages to maintain this pendulum at a vertical degree in a time ts ≤ 1 second, with an entry angle of ± 10 degrees. The Newton-Euler (NE) methodology was used to determine the dynamic equations of motion, by analyzing the free body diagram and using the physical laws that allow defining the forces acting on the system to achieve the state of equilibrium. These simulations were carried out with the SolidWorks (SimMechanics Link) and Matlab (Simulink) tools, in addition a closed loop system was used to analyze the output signal Y (s) with respect to the input signal U (s). The contributions of this development consist of designing high-precision controllers with the purpose of improving industrial automation processes from the implementation of a control system, in areas such as robotics, marine vehicles, aerospace, to name a few examples.