We built a magnetic stirrer to mix tea and honey and developed a method to determine the homogeneity of the mixture based on the variation of light intensity of a laser beam with time due to its scattering by the mixture. The addressed problem was that of mixing tea and honey as fast as possible with a power limitation of one single 1.5 V battery, following the statement of Problem 15 of the 9th International Physicists’ Tournament. The influence of temperature and honey concentration on the total time of mixing was studied through the performance of several experiments reported here. In the best configuration of parameters, the total mixture occurs in less than 2 s, while in the worst configuration, the time necessary reaches 10 s. Results validate the magnetic stirrer as a proper device for mixing tea with honey and light attenuation as an excellent physical property for investigating the homogeneity of the mixture of the honey in tea. Supplementary investigations were made exploring the influence of adding sugar and or a slice of lemon to the tea.

In this work we studied the sound produced by the movement of a hex nut inside an air balloon. We demonstrated, by experiments with hex nuts and nuts without edges, the importance of the nut edges for the production of the screaming sound. Our experimental results show that the most intense frequency of the sound spectrum is directly proportional to the hex nut’s speed of translation, while inversely proportional to its lateral length, thus allowing one to predict the most intense frequency generated by this system.