## 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.

• #### Theory

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.

• #### Tools

Thermal imaging camera, polystyrene mat (we used a tray on which packaged cheese is sold), rubber mallet.

• #### Procedure

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.

• #### Sample result

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.

• #### Technical notes

• 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.

• #### Pedagogical notes

• 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 Thermal Conductivity of Plastic and Metal II. deal with thermal conductivity in more detail.

• #### Similar experiment

Instead of kinetic energy of the mallet we can use the energy of a free fall – see the experiment Conversion of Kinetic Energy to Internal Energy: Falling Weight.