Christmas Sleigh Cakes

head elsewhere

I was impressed by recent stories of forgotten baby all day in the car . Pathological distraction? Not at all: their mothers seemed quite balanced mentally. By cons they were all in shock of a violent injury on the morning following a car accident, another child in hospital etc.. These tragedies illustrate dramatically how an excess of emotion can alter our lucidity. Without falling into these extremes, we become quickly distracted or swayed when our mind is too busy with something ...

attentional neglect

You may know this famous test. You should count on this video the number of passes that making the team black. Stay focused and look good ...

Between half and three-quarters of those who see the video does not notice the gorilla that arises among the players. Our brain is a wonderful machine, but it can focus its attention on one thing at a time. Busy counting the passes are usually zap the incongruous detail when nothing alerting us (the effect succeeds best when the gorilla enters quietly among the players and the color fades among them). This focus of attention is the basic recipe for all magicians: while a dove emerges from their right hand to which they look, no one watching what their left hand. Here is another less known example that the gorilla:

did you fall into the trap, alert cards and the hands of magicians? The window of attention is certainly very close ... Some researchers even believe that onl can not realize that a color or a geometric shape at a time. Here the experience inspires their hypothesis: you have successively and very quickly two images each representing a different pattern (a red square and a blue square) on a panel. You will not have much trouble remembering the location of each pattern and color. If we now present to you the complete picture quickly with two designs, you will remember their arrangement but have more difficulty remembering their respective color.

source: the article by Huang and Pashler Treisman

The effect is multiplied when multiple colors, patterns and more several possible locations. The authors conclude that awareness of a complete composite image requires slowly sweep the whole image of the look and provide a voluntary effort of attention to grasp all its aspects (colors, patterns etc.). Only in that movie heroes remember all the peripheral details of a scene. Especially as if emotion comes into play we saw in this post as attention focuses more on the center of the scene (the famous "weapon effect").

Thought and bulimia
The focus of attention also reduces our powers to decide in conscience. In a series of experiments very fun U.S. researchers asked students to draw lots for an envelope containing a number to remember. For some (group 1) the number was in double digits and others (group 2) was a 7 digit number. The instruction was to remember this number and go write it on the other side of the building. Along the way, students were invited to a drink and a snack. They had a choice between chocolate cake and a fruit salad, before continuing their journey. The whole purpose of the experiment was in fact not to assess their memory, but to observe what they chose to eat. Very strangely, the students of Group 2 having to remember many succumbed much more often (63%) to the temptation of junk food than group 1 (41%). You said weird? What relationship between the size of numbers to memorize and Miss students taste? The researchers' explanation is as follows: our working memory can store up to seven things up, and beyond requires the use of mnemonics. Absorbed by the effort of memory, Group 2 students no longer sufficient mental resources to resist their impulses greedy. Under the effect of this "cognitive overload, they choose the most mechanically tempting dessert. Students in Group 1 did not have this problem because their effort does not require memorizing their attention. They can easily dedicate a few microseconds of their mental processor to select a dessert and sometimes prefer something healthy. The contrast is even greater for individuals to impulsive nature: in a situation of cognitive overload 80% prefer chocolate cake while only 40% in normal times.

Consumption or compensation?
This natural weakness can be exploited by marketing? The over-abundance of stress that flooded the consumer point of sale makes it more sensitive to the temptation? We have not direct evidence, but experience made in 2007 attempted to measure the link between consumption and psychological stress. We asked college students to exercise free association of thoughts. Some of them were instructed to not think of a polar bear (why a polar bear, who knows ...), while others were free to think what they wanted. Then distributed to all $ 10 Reward they could spend in the store or keep for college later. The college banned polar bear ("Thought Suppression" on the graph) have spent much more than the control group ("No Clear") especially when they are naturally impulsive ("High BIS"):

Source: article Vohs and Faber

Here you can not really talk about cognitive overload, since students have completed their exercise time to buy. The need to consume seems more related to lax their self-control, like a muscle that relaxes after having been requested. And more effort was, the greater the need to compensate is important. We love a little extra after a little effort, but in case of prolonged and intense stress, the need to compensate can become pathological, bulimia or binge buying as uncontrollable mood. A feeling of sadness reinforces the need to consume and also if you are disgusted, one tends to get rid at any price that you want to sell: after a national humiliation Cup Worldwide, eBay must be rubbing their hands!

Go, by popular demand, a small digression on the shopping spree ...

Compulsive Buying touch-of-site after more than 1% of the population, women 80% and over three-quarters of them are for clothing and shoes in particular. Wondered why my shoes Xochipillette? Nature and Science are silent on the subject, cons female blogs are full of scientific theories on the subject. Nineteen pairs on average for American women. And it admits 12-over 100 at home! Everything starts with the procurement process brilliantly described by this site (in English):

The expert of the subject are a multitude of reasons why the shoes are ideal Compulsive buying:

1) They easily reflect the mood of the moment, although it is basically dressed, and besides you can afford a much more fancy with his shoes with the rest of his wardrobe.

3) The shoes are the first thing a woman looks at somebody (apparently?).

4) You can always put his shoes even if you have gained or lost 20 kg 10kg.

5) The shoes are are the only clothes we see in full when they are worn on

6) Cinderella won the Prince Charming with his slippers vair glass.

Personally I have a simpler explanation: a beautiful shoe has all the attributes of a jewel and is the only jewelry a woman can afford under the pretext of utility and comfort for walking ...

Sources:

Baba Shiv and Alexander Fedorikhin: Heart & Mind in Conflict

Vohs & Faber: Resources Spent: Self-Regulatory Resource Availability Affects Impulse Buying

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The Jabulani will it take for a banana?

The balloon of the World Cup - the Jabulani -seems to be a nightmare for the guardians of purpose, as its trajectories are unpredictable. On strikes far, he sometimes "float" in the air, wavering in its path before taking the goalkeeper by surprise as this goal of China against France.


Most explanations of these shots floating (eg here or at Tom Roud ) involve "Magnus effect", known to be originally very famous shots "banana"


admit that the parallel between the two types of shots did not seem obvious: the trajectory of the ball floating curve is much less than that of "shooting banana "and the ball seems to be much less" brushed ". Is this really the same effect? The Webinet is investigating this crucial issue which at least has the merit not to mention the antics of the France team. And this week, I promise: no equation!

Shooting banana
To peel the banana, nothing beats the legendary Roberto Carlos free-kick against the team of France in 1998:

Watch as the ball spins very fast on itself. The effect gave the ball causes air on contact, speeding the flow on one side and slowing the other. But the speed of a gas is related to its pressure (remember Bernoulli's theorem and its ): if its speed increases its pressure decreases and vice versa. The pressure differential induced on both sides of the ball creates a lateral pressure that bends its trajectory. That's the famous Magnus effect:

The Magnus effect (the illustration is adapted from this site )

This effect is accentuated by the deviation of the drag of air behind the ball. Under the effect of rotation, the turbulent wake is offset from the axis of movement of the ball:

(source: here )

In response, the ball undergoes a second lateral thrust which s 'added to the Magnus force:

(illustration drawn and adapted from this site ):

Effect will be even stronger than the bullet "Grip" the air around her. That's why the new tennis balls are more effective than bullets or wet waste and bullets baseball have fun sewing.
The speed of the ball itself also enhances the effect: it must "brush" the ball with his foot or his racket, especially in tennis where the ball is very smooth. In football the effect is more readily available in dry weather, this boot gives greater effect to the ball and better ball causes the air around her.
To these effects in the air there are others even more evil when the rebound when the ball is light. This allows for services formidable ping-pong

The second effect kiss-cool banana
In football the true magic touch of banana shot from Roberto Carlos, does not rebound, but the sudden change of the trajectory of the ball, once it has passed the wall of players. The ball seemed misplaced sharply angled towards the goal, taking everyone by surprise.

What happens there? When the ball slows down the flow of air around her suddenly changes of regime, and a password mode "turbulent" is chaotic to say to a much more stable ("laminar" ) where the effects of air viscosity on the ball (and thus the lateral pressure it undergoes) are much greater. If the ball has kept enough of rotation when it enters this regime the curvature of its trajectory is sharply intensified and took everyone by surprise.

source here

short, to make a beautiful shooting bananas should be kicked very powerful and brushed. The ball then follows a trajectory which rounded the curve is accentuated when the ball suddenly changes from turbulent to laminar fashion. This is obtained more easily in dry weather and with a ball "grip" good air.

The ball floating
Let us loose on penalties. Volleyball is that it comes most readily to "float serve." This is obtained when it hits hard in a beach ball very lightly. Even without wind, it looks like the ball did anything. Without a nice video on a good float serve, here's the animation that gives Wikipedia :

The explanation is more subtle than that of 'Magnus effect. Here is the lack of rotation of the ball which causes instability of the trajectory. And yes! In aerodynamics, the rotation plays the same a stabilizing role in mechanical gyroscope , although the mechanisms are very different. It is no coincidence that all the barrels of guns are rifled. Whatever its nature torpedo, or bullet-arrow a shot that turns into a spin during the race still sees its steady path, because the turbulence of the air is channeled behind him.

If instead the ball goes very quickly without turning, the turbulent flow of air in contact creates mini-whirlpools on its surface. These small perturbations are randomly distributed around it are micro-depressions attract or repel the ball from one side or the other. Its trajectory becomes unpredictable and it is precisely this effect which is sought in ball games. The effect is easier to obtain with a bullet llisse and lightweight which is why he is best known ping-pong and volleyball than football. To pass a floating shot must hit the ball sharply to the center (to avoid rotation) and strong (she goes to steady "turbulent").

Verdict ...
recap: Magnus and floating effects have much in common (powerful shot, struck from afar and unpredictable path), but these similarities hide very different mechanisms: the Magnus effect recquiert a ball that spins very fast on itself and becomes dangerous if it is prolonged when the ball slows down. Unlike a floating shot when the ball is in full speed and it does not turn on itself. The Jabulani, smoother and lighter than other models of balloons (especially when played at high altitude) is an ideal candidate for firing "floating", especially when it rains. However, if my explanation is correct it is less susceptible to the effects much worse Magnus. Brief does not float a banana and a shot floating banana does not ...

Source:
Excellent work of students from Strasbourg on the topic
The science of soccer on the site of the University of Hong Kong
The conference "Balls and Ball" Etienne Guyon
Article on Wikipedia the volleyball float serve

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The bike's physics!

I took my best dish bike down a road Corsica, in a hairpin turn. I was not going particularly fast but my wheel was literally taken off in the curve, but I understand why. Only 25 years later, falling on a physics course by Walter Lewin of MIT I understand what happened and also lots of other s funny stuff about things turn. If English does not reject you, and you keep a painful memory of your high school physics course, jettez a look there. It is an extraordinary lesson in pedagogy to put all hands of teachers of physics.

Laws rotation
To understand how it works you just need a little reminder about the laws of motion of a rotating object on itself (but in the words of Arthur commentary, mathophobes can skip the next paragraph without problem). Do not worry it's easy

Simply replace:	by:
speed v	speed ω
mass m	the moment of inertia I = Σ (m i r i ²)
momentum p = mv	angular momentum L = I ω
force F	torque: C F = x r equal to the product of force by the distance to axis and perpendicular to both vectors

(vectors are in bold)

All the laws of motion are deduced from these analogies:

	In a move straight :	In rotation:
equation of motion:	force F = d p / dt	torque C = d L / dt
kinetic energy	E = ½ mv ²	E = ½ Iω ²
Labour	W = Fv	W = CW

When the angular momentum is conserved
If you do not follow, again, no big deal. The only thing that matters today is that in the absence of torque (ie force exerted on the axis of rotation), the angular momentum L = I ω is preserved, which is equivalent to the invariance of the momentum p = m v in the absence of force. It means nothing to you? This is the famous trick of the ice skater who turns on itself more and faster when it withdraws into her own arm and free foot. As it brings some of its mass toward the axis, its moment of inertia I = Σ (m i r ² i) decreases. Since the product I ω remains constant, the speed of rotation on itself ( ω) increases: that is why our beautiful skater speeds up when she cowers.

In a less gracious kind, when the volcano-which-does-anyone-know-it-pronounce name spits a lot of lava, it slightly changes the moment of inertia I of the Earth. And as I ω = constant, the speed of rotation of the Earth itself varies very slightly !

Bike Lesson No. 1: how to turn?
Let us return to my bike. I always hesitate to look me in the turns, lest it does drive out the wheel. This time, I were well kept because of gravel on the road, I simply turn the handlebars into the turn while remaining perfectly vertical. And then, boom ...
What happens when you try to rotate to the left a bicycle wheel spinning:


If the wheel was at rest, she would gently rotated in the direction where it grows. but when she turns it on the flip side! This gyroscopic effect is actually simple to understand: just remember that the axis of rotation of the wheel is still aligned with its angular momentum (remember L = I ω and ω represents the axis of rotation of the wheel). When you push on the axle of the wheel so it creates a pair angular momentum L two additional perpendicular to the thrust. The axis of rotation deviates so towards the new angular momentum.

Application to turn bike (or motorcycle) when driving and the handlebar is turned horizontally, it creates an angular momentum oriented vertically. (Remember the angular momentum is created perpendicular to the thrust on the handlebars). The axis of the wheel will therefore deviate towards the vertical, the wheel is not perpendicular to the road and flip the bike ...

So how do you turn the wheel while leaving the well perpendicular to the road? This is the ABC of the bike drive: just tilt the side where you want to rotate. Strangely to be very stable in a turn you must push down and certainly not turn the handlebars to the horizontal as I did.

Demonstration live when you are on a swivel stool:

The gyroscopes in action

are used to these strange properties to guide satellites in space and stabilize their position using small rotors attached to the satellite. Just change the orientation of the rotors slightly so that the satellite rotates on itself as in the previous experiment.

Now that the bike has no more secrets for you, you are ready to understand how a gyroscope can defy gravity. Take a bicycle wheel, rotate it on its axis and place its axis horizontally on a support:

The wheel not fall as he would if he were arrested, it turns around its horizontal support! A return to Newton in his grave? Not really: we are dealing exactly the same phenomenon as above, except that the gravity of the wheel (and opposite reaction of the support) replace the strength of the guy sitting on the stool swivel vertically when pressed on the axle of the wheel. If the speed of rotation of the wheel is great, the wheel turns to try to orient its axis of rotation to the angular momentum created by the weight of the wheel. Without ever succeeding course since the couple is still in the plane of the wheel. Just like the donkey who advance to catch the carrot hanging in front of his nose. More wheel weighs heavy more quickly it turns around the support.

Such "resistance" to gravity explains why a bike ride is stable vertically. And why a coin when you ride long lance on its edge. Gyroscopic phenomena also allow all sorts of pranks. Stash a wheel that rotates in baggage for instance and you get a bag very facetious:


Go to surpassing these adventures bicycle, a riddle: what goes down the more fast slope coasting:
- a large or small wheel?
- a solid wheel or a wheel "normal"?
- a heavy wheel or wheel light?

Curiously, the speed does not depend on the size of the wheels, or their mass ... Cons by a solid wheel moves faster than a hollow wheel because its moment of inertia from the center is smaller.

The acceleration is independent of the mass (M), radius R and is sixth times greater for a solid cylinder as a hollow cylinder

Demo image:

I guess that's why the wheels of the track bikes are solid discs. But in windy, beware of risks off!

Source:
Courses Walter Lewin (8.01) which are extracted from the MIT videos of this post.

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Windows on Court: The Sketch Commune 2010


Since 1984, the Higher Institute of Architecture Victor Horta annually organizes the common outline. This brings urban laboratory for a week, all student-architects of the Institute. He offers to walk and invest extraordinary place, with their best tools: imagination and creativity!

The rules are simple:
• A theme for the week ...
• An extra-ordinary place in Brussels ...
• A question, to which reference should meet full-scale ...

With an ambition citizen: offer people a fresh look at our city. By ephemeral installations, the work aims to transform the vision of the everyday environment, suggest new ways to perform familiar spaces and transformed well-known places so they become transparent.
Throughout this workshop, students are accompanied by many ancient architects Institute graduates, artists and faculty.
During this week of creative excitement, cultural and friendly school expatrie extramural, and food for thought for students, the Outline Common organizes many events open to all conferences, debates, meetings with stakeholders of urban life,
... This year's event is part of the 175th anniversary of the ULB and Night Lights May 7, 2010.
facilities students will also participate in the Iris Festival on 08/09 May 2010!