Mechanical sensors and plastic syringes to verify the gas laws without neglecting friction

Two experiments are proposed to study Boyle's law and the pressure law in a school laboratory. The peculiar feature of the experiments is that the value of the pressure and of the volume are obtained respectively by means of a force and a position sensor, thus allowing students to connect, in an experimental context, mechanics variables, such as force and position, to thermodynamics ones, such as pressure and volume. Focusing on forces requires that students take into account the role of the friction force on the plunger, a force that is generally disregarded in standard experiments. Considering friction forces helps students to realize the complexity of a real experiment and appreciate the value and the limits of a quantitative measurement. (Contains 4 figures.)