The development of demonstration experiments plays a key role in modern and efficient teaching of physics, chemistry, biology and several other disciplines. Today's computers and electronic devices allow the use of simple software-based instrumentation to achieve flexible and surprisingly transparent experimentation, however, the professional solutions are rather expensive while the "home-made" instruments are often inaccurate and the software can be inconvenient and didactically questionable. There are several attempts to solve these problems and make experiments accessible for almost every teacher and student. In this paper a very simple, ultra low cost, easy-to-make sound card based high-resolution stopwatch will be shown that supports a wide variety of mechanical experiments. Here we present two kinds of experiments, with which we can demonstrate well the usefulness of our device: measurement of the moment of inertia, and study of free-falling balls. We also show how these kinds of measurement methods develops different competences of the students.