Test your knowledge!

Easy quiz!  

  1. What is the name of our galaxy?…………………………………………………………………….
  2. When did we discover that there were billions of galaxies in the Universe?………..
  3. What did Einstein discover about space?………………………………………………………..
  4. What is the name of the singularity which created the Universe?………………………
  5. What three atoms were created during this phase?………………………………………….
  6. Where do all the other atoms (in Mendeleïev’s periodic table) come from?………..
  7. How old is the Universe? And the Earth?………………………………………………………..
  8. What sort of particles are called Beauty and Charm? Where are they?……………….
  9. Why is it impossible for mankind to go to another planet?………………………………..
  10. What ultimate theory are physicists looking for?……………………………………………..

 

The secret inhabitants of our body…

THE SECRETS OF THE MICROBIOTA

A microbiota is « the ecological community of commensal, symbiotic and pathogenic microorganisms that literally share our body space ». Joshua Lederberg coined the term, emphasizing the importance of microorganisms inhabiting the human body in health and disease. Many scientific articles distinguish microbiome and microbiota to describe either the collective genomes of the microorganisms that reside in an environmental niche, or the microorganisms themselves, respectively.

The microbes being discussed generally do not cause disease unless they grow abnormally ; they exist in harmony and symbiotically with their hosts. The microbiome and host may have emerged as a unit in the process of evolution, so we now speak of co-evolution, an aspect Darwin had not foreseen.

The human microbiota includes bacteria, fungi, and archaea. The human microbiome refers to their genomes.

 

Humans are colonized by many microorganisms: the traditional estimate was that humans live with ten times more non-human cells than human cells, so we are only 10% human. The microbiota that colonize humans have not merely a commensal (a non-harmful coexistence), but rather a mutualistic relationship with their human hosts. Some of these organisms perform tasks that are known to be useful for the human host; for most, the role is not well understood. Those that are expected to be present, and that under normal circumstances do not cause disease, are deemed normal flora or normal microbiota.

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The Human Microbiome Project (2008-2012) took on the project of sequencing the DNA of the human microbiota, focusing particularly on the microbiota that normally inhabit the skin, mouth, nose, digestive tract, and vagina. They discovered thousands of new species!

 

 

 

 

What is time?

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Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future. Time is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as the fourth dimension, along with the three spatial dimensions.

Time has long been an important subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields has consistently eluded scholars. Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems. Two contrasting viewpoints on time divide prominent philosophers. One view is that time is part of the fundamental structure of the universe—a dimension independent of events, in which events occur in sequence. Sir Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. The opposing view is that time does not refer to any kind of « container » that events and objects « move through », nor to any entity that « flows », but that it is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled.

Time in physics is unambiguously operationally defined as « what a clock reads. » Time is one of the seven fundamental physical quantities in both the International System of Units and International System of Quantities. Time is used to define other quantities—such as velocity—so defining time in terms of such quantities would result in circularity of definition. An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, is highly useful in the conduct of both advanced experiments and everyday affairs of life. The operational definition leaves aside the question whether there is something called time, apart from the counting activity just mentioned, that flows and that can be measured. Investigations of a single continuum called space-time bring questions about space into questions about time, questions that have their roots in the works of early students of natural philosophy.

Furthermore, it may be that there is a subjective component to time, but whether or not time itself is « felt », as a sensation, or is a judgment, is a matter of debate.

Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined by measuring the electronic transition frequency of caesium atoms. Time is also of significant social importance, due to an awareness of the limited time in each day and in human life spans.

Etude des arcs-en-ciel par les 2ndes 2 en Sciences et Laboratoire

Au cours de cette séquence, nous avons eu l’occasion d’étudier la formation d’un arc-en-ciel, et de réaliser une expérience à ce sujet.

Pour commencer, nous avons réalisé une affiche explicative sur le fonctionnement et la création de l’arc-en-ciel.

Affiche explicative réalisée en classe
Affiche explicative réalisée en classe

Cette affiche nous explique la formation d’un arc-en-ciel, simple ou double.

 

Le phénomène des arcs-en-ciel, comment l’expliquer ?

La formation d’un arc-en-ciel est due à la conjonction de trois éléments : il est nécessaire d’avoir une source de lumière blanche, une présence d’eau (vapeur d’eau, fines gouttelettes) et la position de l’observateur est également importante.

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Pour observer un arc-en-ciel, l’observateur doit se trouver dos au soleil mais devant les gouttelettes d’eau.

Comment cela se déroule-t-il ?

Les rayons lumineux traversent les gouttes d’eau. On alors observe un arc-en-ciel à environ à 40° par rapport à l’horizon, et le second à 50°.

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Cela peut s’expliquer par :

Les rayons lumineux qui entrent dans la goutte. Celle-ci décompose la lumière du rayon, le rouge le plus haut dans la goutte et le violet le plus bas. Les rayons se reflètent au travers de celle-ci et ressortent.

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Si on le voyait en entier, il aurait une forme circulaire plus précisément une forme ovale : une ellipse.

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On ne peut pas le voir en entier à cause du plan antisolaire. C’est à cause de la terre qui bloque les rayons du soleil et les empêche de former un arc-en-ciel entier.

Créer un arc-en-ciel:

Ensuite, nous avons réalisé l’expérience suivante pour approfondir le sujet.

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Matériel utilisé :
  • Une bassine
  • De l’eau
  • Un miroir
  • Une feuille blanche
  • Une source de lumière blanche
Protocole:
  • Tout d’abord il faut remplir la bassine d’eau, puis y introduire la moitié inférieure du miroir avec une inclinaison à 45°.
  • Ensuite, pointer ou diriger la source de lumière blanche vers le miroir.
  • Enfin, positionner la feuille au-dessus de la source de lumière blanche et de la bassine et chercher où le miroir reflète la lumière. On obtient alors un petit arc-en-ciel.

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Article original de Marine B. , Alexane P., Andgèle P. et Saïd A.