Ronai Lisboa

We present and discuss, from a kinematic point of view, the dance movement known as the Moonwalk, popularized by Michael Jackson over 40 years ago. This paper explores the application of kinematic analysis to enhance physics education by examining the Moonwalk movement. We use the free software Tracker to register the position and time of three material points: the head (H) and the tips of the right and left feet (RF, LF) for two dancers. We found that head movement is well described by a constant speed model and the foot-to-head speed ratio close to the expected value of 2. We also observed an asymmetry in leg movement that impacts the speed of the feet in relation to the dancer’s head. We conclude by discussing possibilities for using dance and other body movements as motivation for physics classes at the high school and university level.

A determinação da aceleração de queda livre é uma prática comum em laboratórios didáticos de Física. Neste trabalho, apresentamos uma proposta experimental para medir a aceleração da gravidade baseada em um exercício do livro didático de Mecânica do professor Moysés Nussenzveig. Essa determinação é realizada através do movimento de um carro sobre um trilho de ar inclinado, e possui discrepância da ordem de 0,5%.

Measuring the acceleration of a glider on a slightly inclined air track is a typical activity in different experiments in didactic physics laboratories. In this paper, we discuss acceleration measurements derived directly from the quantity Δ v /Δ t , testing its reproducibility with several time sensors (photogates). Using a standard lab equipment we show that acceleration measurements using two photogates strongly depend on the photogates used and even on the distance between them, what can frustrate the goals of the experiment. The technical aspects behind that unexpected behavior can be partially overcome by working with a single photogate in a method where the glider is launched uphill and its speed is measured in the ascending and the descending motion. Using this alternative approach we were able to reduce discrepancies by a factor of 6, down to less than 1%. For both methods, the systematic errors between photogates surpass the statistical uncertainties for each photogate. Finally, we show that these discrepancies can be explained by an offset of the order of 1 ms in time measurements.

Background: Unbound single-particle states become important in determining the properties of a hot nucleus as its temperature increases. We present relativistic mean field (RMF) for hot nuclei considering not only the self-consistent temperature and density dependence of the self-consistent relativistic mean fields but also the vapor phase that takes into account the unbound nucleon states.

Spin and pseudospin symmetries in the spectra of nucleons and antinucleons are studied in a relativistic mean-field theory with scalar and vector Woods-Saxon potentials, in which the strength of the latter is allowed to change. We observe that, for nucleons and antinucleons, the spin symmetry is of perturbative nature and it is almost an exact symmetry in the physical region for antinucleons. The opposite situation is found in the pseudospin symmetry case, which is better realized for nucleons than for antinucleons, but is of dynamical nature and cannot be viewed in a perturbative way for either nucleons or antinucleons. This is shown by computation of the spin-orbit and pseudospin-orbit couplings for selected spin and pseudospin partners in both spectra.

We study the effects of temperature andpairing on pseudospin symmetry in spherical and deformed nucleus using the Dirac—Hartree—Bogoliubov (DHB) formalism. We include temperature in the DHB equation using the Matsubara formalism and analyze changes in the neutron single particle levels with the temperature. We show that the effect of temperature on the pseudospin energy splitting is small. We find that this splitting decreases at high temperatures and that pseudospin partners are almost degenerate in deformed hot nuclei, indicating the dependence of pseudospin symmetry on the nuclear surface. Furthermore, for reasonable values of the pairing interaction, we also show that pairing does not affect the pseudospin symmetry in deformed nuclei. Finally, we find that the effect of temperature on pseudospin doublets is more pronounced in spherical nuclei than in deformed ones.