The movement of athletes is one of the most interesting subjects of kinematic study. The precision of gestures, the transformation of energies, the complexity of trajectories are all exciting subjects to study for the student, in a field that is generally familiar to him. In this post, we analyze the most complex discipline of athletics: pole jumping. This movement is interesting because it makes it possible to study the multiple transformations of energy: kinetic energy of the race first, elastic energy of compression of the pole then, then potential energy of the jump. The video we are going to study is in the Resources area where we have collected many videos for the classroom study of kinematics: www.fizziq.org/cinematique. It is also accessible directly from the FizziQ application. This video is reconstructed in a fixed shot from a film of the 2015 Shanghai IAFF championship.
Let's analyze this movement in the FizziQ application. If this is your first use of the Cinematic module, you can consult the Help section at the bottom of the page. 1. Analysis of the trajectory
Let's first look at the trajectory of the perch. In the selection of data, we choose the time and positions x and y, then transfer the data to the experience book for graphical analysis. We visualize the overall movement of the athlete using the xy graph. This graph allows us to identify the different stages of the movement: horizontal race, ascent phase, progressive at the beginning, then vertical, reaching the peak at 2.4 seconds, then fall on the carpet. By watching the video we can also identify particular movements that we will come back to when analyzing energies: the reversal that consists of a rotation of the body, and the straightening during which the pole straightens up and the perch continues to propel itself upwards. 2. Analysis of speeds
Now, let's look at the athlete's horizontal speed. Up to 0.8 seconds, the race is done at constant speed. When the pole comes tore against the stop, the horizontal speed drops linearly while the pole compresses and slows down horizontal movement. This phase is over, when the pole is vertical and relaxed, the horizontal speed is constant since the athlete is not subjected to any horizontal force. It is interesting to note that, in the ascent phase, the horizontal speed decreases linearly, which would suggest that the horizontal compression force exerted by the pole is constant.
The study of vertical speed makes it possible to better visualize the phase during which the pole is released. On the video, the pole fully relaxes at 1.9 seconds. At this time, the athlete no longer seems to be able to use the pole support to benefit from additional vertical acceleration and the only force that is then exerted on him is weightlessness. The peak is reached when the vertical speed is zero, around 2.4 s.
3. Energy analysis
The most interesting analysis to be carried out is the energy balance that can also be done with FizziQ. We assume here that the athlete's weight is 55 kg. What does this analysis give? First of all, we note that the potential energy gain between the beginning and the end of the movement is slightly greater than the initial kinetic energy. It is therefore not simply the energy of the initial race that is transformed into potential energy but also the energy injection of the perch during the flight phase, which makes it possible to compensate for energy losses due to friction and shocks but also to go higher. There are two phases of energy supply: the reversal towards 1.3 s in which the athlete uses his abdominals to rotate and the straightening towards 1.8 s where he extends vertically and pushes on the pole.
Turn-around phase
Recovery phase:
Can we estimate the athlete's energy intake during the flight phase? If we neglect losses, at the maximum compression point, we can estimate the elastic energy which is the difference between the initial mechanical energy and the mechanical energy at this point, i.e. about 1300 J. The potential energy needed to move from the turning point to the peak being about 2000 J, an energy supply of the athlete during the flight phase is calculated of at least 700 J, the equivalent of a height gain of at least 1.30m! We can clearly see the complexity of the pole jump movement, which requires both to ensure the good transformation of the race into elastic energy and its restitution into potential energy, but also to provide additional energy during the flight phase to gain even more than one meter! What coordination!! In conclusion In a few minutes we were able to carry out a study of a complex movement, that of a perch. The analysis we have just done is succinct but we see, however, that we can very quickly obtain very interesting intuitions about the physics of pole vaulting and, why not, ask ourselves the question of the improvements that the athlete could make to his movement in order to make the most of the laws of physics! From a pedagogical point of view, the situation immediately challenges the student, and shows him the usefulness of learning the sciences to understand the world around him. Perch jumping is a very special sport but similar analyses can be made on football, basketball or other sports whose videos are accessible in the cinematic library. But we particularly encourage students and teachers to make their own videos, and why not, to share them with us for their integration on the FizziQ website! To learn more about the kinematics of pole vaulting, you can consult the article "Energy study of pole vaulting" by Rémi Carmigniani, Christophe Clanet, Quentin Lustig and Sébastien Homo To learn more about cinematics and sport, you can visit the École Polytechnique website on this subject: https://www.polytechnique.edu/fondation/actualites/toutes-les-actualites/sport-handisport-la-physique-au-service-des-athletes Help with the handling of FizziQ: - to take your first steps with the Kinematics module, consult our Knowledge Base > FizziQ > Kinematics: first steps - to download a video from the Kinematic Videos area or from a file located on the Internet, consult our Knowledge Base > FizziQ > Kinematics: download a video