How to launch a rubber band (Comment tirer un elastic)

Scientists are taking aim at the physics of rubber band bombardments.

Using high-speed video, researchers have analyzed what happens to a rubber band when it’s launched from a thumb. The results offer some tips for how to make a clean shot, Boston University mechanical engineers Alexandros Oratis and James Bird report in a paper in press in Physical Review Letters.

The researchers focused on one particular shooting technique: Elastic is slung around the raised thumb of one hand and pulled back with the fingers of the other hand. Standardizing the operation by using a cylinder rather than a thumb, the scientists filmed the details of the shooting process.

When the rubber band is let loose, a release of tension in the band quickly travels toward the cylinder. Meanwhile, the band itself zings toward the cylinder at a slower speed than that tension release, the scientists found.

When shot off a thumb, the band’s forward motion could lead to a rubbery rear-ender, with the thumb getting in the way of the elastic and sending the band askew. But if the feat is performed properly, the release of tension causes the thumb to duck out of the way before the rubber band reaches it. The band then sails past, buckling into a wrinkly shape as it shoots by.

By testing different shooting strategies, the researchers zeroed in on some guidelines. Don’t pull the band too tight: The extra tension increases the flight speed, so the thumb doesn’t deflect fast enough to avoid it. And a wider elastic band is preferred. That’s because the thumb must exert more force against the wider band, so that when the band is released, the digit falls away more quickly, making the elastic’s getaway easier.

 

Source : of https://www.sciencenews.org/article/high-speed-video-reveals-physics-tricks-shooting-rubber-band

Processus d’évaluation : « Etre premier en ordre de passage vous pénalisera »

Processus d’évaluation : « Etre premier en ordre de passage vous pénalisera »

Une expérience américaine montre que les évaluateurs octroient de meilleurs scores au fil du temps, observe Charles Cuvelliez, professeur en communication, dans une tribune au « Monde ». Un biais cognitif qui pèse lourdement sur la rationalité de nos décisions.

Si décider de votre horaire de passage à un concours vous a toujours angoissé, vous avez bien raison car c’est loin d’être un détail sans influence sur le résultat. C’est la leçon d’expériences menées par deux chercheurs de l’université de Virginie, qui ont mis en évidence un nouveau biais cognitif (« Do Evaluations Rise With Experience ? » Kieran O’Connor, Amar Cheema, Psychological Science n° 29/5, 1er mars 2018).

Ils ont demandé à un groupe de 168 étudiants de donner un score à dix histoires qu’on leur demandait de lire, à raison d’une histoire par jour, de façon à étaler le processus d’évaluation dans le temps. L’ordre dans lequel les histoires leur étaient données différait selon les étudiants. Or, ce sont les histoires lues dans les derniers jours qui ont eu le meilleur score, peu importe laquelle.

En fait, la note attribuée avait tendance à monter jour après jour. On leur a ensuite demandé, au fur et à mesure qu’ils avançaient dans leur évaluation des dix histoires, de juger la difficulté de cette tâche d’évaluation. Véracité, style, contenu, genre, chacun avait des critères d’évaluation différents, mais tous étaient d’accord pour dire que la tâche devenait plus facile avec le temps.

C’est ce qui fait penser aux chercheurs que notre cerveau confond inconsciemment la facilité à donner un score avec le score lui-même, comme si quelque chose qui devient (plus) facile à évaluer était forcément meilleur ! Et si l’on peut parler de « biais cognitif », c’est parce que les participants étaient persuadés d’évaluer de la même manière au début du test comme à la fin.

L’objectivité existe-t-elle ?

Si on fait le bilan de toutes les situations où une estimation s’étale dans le temps, cette expérience est riche d’enseignements. Passer le premier ou le dernier à l’épreuve orale, c’est un dilemme auquel tous les étudiants font face.

Source : Le Monde

 

Tableau des Troubles Dys

 

 

On regroupe sous “troubles Dys” les troubles cognitifs spécifiques et les troubles des apprentissages qu’ils induisent.

Les troubles cognitifs spécifiques apparaissent au cours du développement de l’enfant, avant ou lors des premiers apprentissages, et persistent à l’âge adulte.

Ils ont des répercussions sur la vie scolaire, professionnelle et sociale, et peuvent provoquer un déséquilibre psycho-affectif. Leur repérage, leur dépistage et leur diagnostic sont déterminants.

Lire la suite : http://www.ffdys.com/troubles-dys

Physionary - a scientific version of Pictionary

Physionary - a scientific version of Pictionary

N. Poljak, A. Bosilj, S. Brzaj, J. Dragovic, T. Dubcek, F. Erhardt, M. Jercic
Physics department, University of Zagreb

Abstract. We describe a variant of the popular game “Pictionary” based on the terms used in elementary and high school physics. We believe that the drawing of physical terms helps students develop a deeper understanding of physical concepts behind them, as well as apply them in everyday situations.

1. Introduction

The Croatian Physical Society organizes the annual Summer school for young physicists [1], intended to reward elementary and high school students for their accomplishments on the national physics competitions. The schools typically consists of half-day lectures combined with workshops, experiments or games that take place during leisure hours. For the last three editions of the summer schools, we developed a variant of the popular game ”Pictionary” as a small competition for the students. “Physionary”, as we named the variant, has proven to be very successful in entertaining the students, not only during the evenings intended for the competition, but also during the rest of leisure time.

2. Game description

“Physionary” is a game loosely derived and expanded from the commercially-distributed “Pictionary”. A similar game was developed earlier for University biology students [2], however, we expanded further on the game since we found it beneficial to do so.

The students are divided into groups based on their age and are given a number of cards, each containing 6 terms from elementary or high school physics. The terms are taken from indices of physics curricula or physics manuals and divided into 5 sets of cards, one for each high school grade and one for elementary school grades. A dice is thrown to randomly select the ordinal number of the term on the card. A one minute timer is started and one of the students from each group is required to draw the term found on his/her card, while the rest of the group has to guess what term it is. If the team accomplishes this within the given time allotment, they receive a point. Several rounds are played this way before the pace of the game is then made faster by decreasing the available time for drawing. After a predetermined number of rounds played in this manner, the second phase of the game begins. In this phase, the students don’t draw the terms but instead try to “act out” the term given on their cards, as it is usually done in charades. This is also done within a given time allotment, typically set to a minute.

This game turned out not to be only entertaining, but also highly educational. Sometimes, a specific term may not be recognized by some of the members of a certain group. However, we noticed that the said term is quickly taken in by those members, as evidenced by their future recognition of that, as well as similar terms. Once the students start to communicate concepts pictorially, they move from their definitions and try to use everyday examples to convey them to their group. We have also noticed that a sense of connection between various terms is formed, since the students find it beneficial to explain a new term with the help of terms that they have already drawn on paper - they simply circle the term that was already guessed by the group. Finally, the students were often found drawing graphs and diagrams, which is a skill they need to develop in physics, but are often not motivated to do so.

3. Conclusion

We have expanded on the known popular party games to
create an effective and entertaining physics learning tool.
The skills developed during game play seem to be beneficial
to the students and the terms they are required to draw or
act out are taken from their curricula. The students seem
to develop another important skill during the game - using
simple physical concepts in everyday situations, which is a
skill they are most often found lacking. In what follows, we
present a selection of 10 terms (out of 850) from each of the
5 sets of cards. We have limited the selection to 10 terms
since we expect that different countries will have differing
curricula, so we thought it best that everyone interested
made their own sets of cards. Figure 1: An example of a

playing card.

References

[1] http://www.hfd.hr/ljetna skola/
[2] Kathleen A. Parson, John S. Miles, “Bio-Pictionary – a scientific party game which helps to develop pictorial communication skills”, Journal of Biological Education, 28:1, 17-18, DOI:10.1080/00219266.1994.9655358


elementary

1st grade

2nd grade

3rd grade

4th grade

heat insulator surface area power mass sliding friction Solar energy pulley molecule cavity electricity

joule frequency dynamics buoyancy unit
fluid projectile motion cosmic speed energy Galileo

diffusion capacitor inductivity linear expansion Lorentz force work
ideal gas insulator interaction isobar

diffraction rainbow standing wave intensity sound rotation length contraction phase
lens
light guide

plasma atom antiparticle semiconductor fractal boson
red giant mass defect butterfly effect quark

Table 1. A sample from the terms given on the “Physionary” cards, sorted in 5 classes according to students’ grade.