Conversion of Kinetic Energy into Internal Energy: Blow with a Mallet
Experiment number : 1706
Goal of experiment
This experiment demonstrates that when we hit a mat with a mallet, the temperature of the mat increases.
During the impact, the kinetic energy of the mallet is converted partly into energy of inelastic deformation of the mat and partly into the internal energy of the mallet and the mat. This increase in internal energy is locally manifested by a temperature increase.
Thermal imaging camera, polystyrene mat (we used a tray on which packaged cheese is sold), rubber mallet.
We hit the polystyrene mat with the mallet and monitor the place of impact with a thermal imaging camera. The temperature at the place of impact increases by several °C.
The video bellow illustrates a successful experiment.
During this experiment, a thermal imaging camera FLIR i7 was used. The temperature range of colour scheme was chosen in the interval from 22 °C to 34 °C, emissivity was ε = 0,95.
The experiment can also be performed with an ordinary hammer; however, the temperature increase is not so significant due to the heat conductivity of the hammer.
We do not recommend using a metal plate instead of polystyrene - the heat created by the impact of the mallet would be due to the heat conductivity transferred to the surrounding area.
It is important that students realize that during the experiment not only the temperature of the mat increases, but also the temperature of the mallet increases – this can be illustrated by the thermal imaging camera.
We can connect this experiment with the concept of thermal conductivity. We can ask students, why the experiment showed nothing conclusive, when we used a metal plate instead of a polystyrene plate. In such a case a local temperature increase in the place of impact would be immediately minimized by the heat being transferred to the surroundings. The experiments Thermal Conductivity of Plastic and Metal I. and Tepelná vodivost plastu a kovu II. (in Czech only) deal with thermal conductivity in more detail.
Instead of kinetic energy of the mallet we can use the energy of a free fall – see the experiment Přeměna kinetické energie na vnitřní energii: Pád závaží (in Czech only).
Link to a related task
The task Heating of a Ball Hitting a Wooden Target mathematically describes in detail a conversion of kinetic energy into internal energy.