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The submarines use sonars to know how far away is the sea floor to bottom of the submarine and to detect all kind of object that we can find in the sea with the equation: distance=speed x time / 2

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The principle of non-destructive ultrasound testing (also called ultrasound testing) consists of emitting an ultrasonic wave which propagates in the room to be tested and is reflected like an echo on the obstacles it encounters (anomalies, limits of the room). Ultrasonic non-destructive testing allows:

detect internal defects in different materials
perform thickness measurements on coatings
to check equipment without dismantling
to carry out internal or external corrosion measurements
carry out adhesion and delamination checks
to check the conformity of welds, forging and foundry parts, ceramics, etc.

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Court video to clarify and show by drawings what is an ultrasound.

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How to see with sound - Jacques S. Abramowicz

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The ultrasounds      By Thibault and Julien

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The ultrasounds      By Thibault and Julien

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An ultrasound is a sound that vibrates at frequencies above 20 000Hz, above the range of human hearing.
Some animals like bats or kind of marine mammals use ultrasounds to communicate or to probe.

As humans, we produce ultrasounds thanks to electric devices : we produce electrical oscillations of ultrasounds that are converted into ultrasounds waves.
When a device emit an ultrasounds wave, the wave spreads and when it changes of meduim, a part of the wave is reflected by the meduim to the device the other part pass through the meduim it's the refracted part.

This is very usefull to learn about its internal structure (object, animal, ...).

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Picture of the damage created by the "Big one"

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Here are some of the key facts and dates recorded : 

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Here are some of the key facts and dates recorded : 

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- The 1906 San Francisco earthquake refers to the earthquake that mainly affected San Francisco on the morning of Wednesday, April 18, 1906. It was estimated to have a magnitude of about 7.8 on the Richter scale, and its epicenter was located 12.1 km west of San Francisco. This one caused a fire in San Francisco due to gas ruptures. It caused about 3000 deaths.

- California had to face two earthquakes in two days: one of magnitude 6.4 on Thursday, the other of magnitude 7.1 on Friday. If in Los Angeles, the damage was minimal, these two successive earthquakes created the "Big One", a potentially devastating mega-earthquake so feared in the American West.
This "Big One", measuring 8.5 or more on the Richter scale, occurs every 150 to 200 years and is expected by seismologists to strike California within a few years. Indeed, the last "Big One" occurred in 1857 at Fort Tejon, with a magnitude of 8.3. Another large earthquake struck San Francisco in 1906. With a magnitude of 7.8, it caused the death of about 3,000 people.

- The worst earthquake ever in the Middle East and North Africa occurred on May 20, 1202. This earthquake was considered the worst earthquake known to date, in which about 1 million people lost their lives.

-  An earthquake does not last more than one minute, two; however, an earthquake that shook Alaska, on March 27, 1964, lasted about 5 minutes. Fortunately, there were only 131 deaths. However, the damage caused was extensive and amounted to about $450 million.

- On December 26, 2004, a tsunami was caused by an underwater earthquake which in turn caused catastrophic flooding in Indonesia, Sri Lanka, Myanmar, Maldives, Malaysia, India and parts of Africa, killing more than 283,000 people.

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The speed of the object can be determinate by the amount of shift that takes place in the radio waves
exemple: land in the fog
In the case of planes the radar is going to emit an electromagnetic waves towards the sky.
This waves is going to spread, hit a plane and be reflected by this plane. This reflection goes to the radar antenna and can display the information on the screen. With radar we can see size of the plane because every plane template refers to a specific type of waves. This technic is very useful for the plane so that they don't hit another plane that they wouldn't have seen.

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Examples :
Speed of sound in the air : 340m/s
Speed of sound in water : 4.3 times faster than in air at the same temperature.

-> Sound waves travel faster in denser substances.

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Definition :
It's a mechanical vibration.
Sound waves are successions of molecular compressions and dilatations.
Waves can be reflected, refracted or attenuated by the medium.
Only frequencies lying between 20Hz and 20000Hz are percepted (under 20Hz : infrasound; above 20000Hz : ultrasound).
Sound waves are generated by a sound source.
Sound waves have differents caracteristics : frequency, amplitude, speed and direction.
The behavior of sound propagation is generally affected :
-by the relationship between the density and the pressure of the medium. The relationship is affected by temperature (it determine the speed of sound within the medium)
-the motion of the medium itself
-and the viscosity of the medium.

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Wave is the sea 🌊 by Louise and Candice 

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Wave is the sea 🌊 by Louise and Candice 

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A wave is a regular undulation on the surface of the sea formed by a distant wind.

- On physic, a wave is a mechanical waves that propagates at the interface between the water surface and the air.

- A wave is describe by its wavelength, amplitude, period and speed.

- There is different types of waves ——>

Breaker: when the wind persists, the waves take ampleur. They rise to a critical point and then break and go forward.

Roller: towards the coast the wave is disturbed by the low water level. Here also the waves rise and break forming rollers, very popular with surfers.

Backwash: if a series of waves hits an obstacle such as a pier or the hull of a ship, it goes backwards and creates interference with the other waves.

- Then the particular waves, their are —>

Tidal bore: is a particular wave that occurs at the beginning of a river, due to the wave of the rising tide, it’s visible during high tides.

Tsunamis: giant and devastating waves that are usually caused by the sudden movement of a large volume of water following an earthquake or landslide.

Rogue waves: of enormous amplitude, they are formed at random in the sea, these waves are still quite mysterious.

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Radar = Radio Detection And Ranging
Is a detection system that uses radio waves to determine the distance or the velocity of an object. The first radar was created in 1939 for the red army(URSS🇷🇺)
It producing electromagnetic waves in the radio domain. Radar waves lenght are included between 30 cm and 3m. It can be used by the military for ships 🚢or guided missiles for exemples. A radar system has a transmitter that emits radio waves known as a radar signal in all type of direction. When these signals contact an object, they are  reflected or scattered in Manu directions. Some of them will penetrate into the target🎯 Radar signals are reflected especially well by materials with a lot of electrical conductivity ⚡️Such as most metals ⚙️,sea water 🌊 and wet ground. The radar can determine the movement of the object by the frequency of the radio wave that came back. If the difference between the radio wave emited and the radio wave that came is shifted negative ➖: the object it bounced off of is likely moving  away from the radar 📡⬅️. If the difference is positive➕, that object is headed toward the radar📡➡️. This is the Doppler effect.

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Ultra-sound Echography     by Thibault and Julien

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Ultra-sound Echography     by Thibault and Julien

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The ultra-sounds are used in many areas. In this case the ultra-sounds are used from an echography a part of the ultra-sounds that are emitted are reflected and return to the device that translate the reflection into a picture, like this one. Ultrasound imaging, or sonography, is the use of high-frequency sound waves to visualize soft tissues such as internal organs. The procedure is capable of generating real-time images that reveal movement of the tissues or blood flow.

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A GPS where and why? and how it works? victoire & blandine

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A GPS where and why? and how it works? victoire & blandine

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where and why?
GPS are located at 20 thousand kilometers hight to allow precise géolocalisation on land for vehicules on sea for ships and in the air for planes, missiles and satellites operating in low orbite. One GPS needs four satellites to be able to fonction.
How It works?
GPS satellites send electro magnetic waves which propagate at the speed of light (3.0 x 10^8 m/s). This allow satellites to calculate the distance between the GPS and It, calculating the time that the wave took for travel. For that they use atomic clocks which are extremely precise to find the position.

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The GPS system can also measure the speed of the GPS (S in m/s) receiver on the earth’s surface. It’s called the Doppler effect, which is very precise. It’s a frequency difference (F in Hertz)  between the transmitted wave and the received wave.
Indeed, when the distance between the receiver and the satellites changes, it means that there is a movement from the GPS receiver on the earth.
By measuring the difference between the theoretical signal (without movement) and the received signal (in motion), the GPS receiver can calculate its speed relative to the satellites

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Satellites constantly emit electromagnetic waves on two different frequencies : 1575,42 MegaHertz for the civilian GPS and 1227,60 MegaHertz for the military GPS.
The GPS receiver can locate precisely in 3D each point placed in visibility of the GPS satellites with an accuracy of 3 to 50 meters

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The Greenhouse effect and so the Life on Earth are the results on the infrared radiation.

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Definition: technology that is able to remotely detect infrared radiation with an infrared camera by converting it into an electronic signal which is processed to produce a thermal image. The more it's red, the more it's hot and so infrared.

We can us it for our houses insulation for example because the infrared camera highlights thermal loss and sources of moisture in the house, especially with the thermal bridges (doors, windows, outer walls)
We also use it in medicine to identify tumors like breast cancer or inflammations because it avoid X-ray exposure.

Even animals can see infrared radiation like, for example, snakes so they can capture their future prey in the dark...

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Earthquakes are measured using the Richter scale which is a seismic reference scale established in 1935. The Richter scale, also called the Richter magnitude scale and Richter's magnitude scale, is a measure of the strength of earthquakes, developed by Charles Francis Ritcher and presented in his landmark 1935 paper, where he called it the "magnitude scale". This was later revised and renamed the local magnitude scale.
That evaluates the energy released at the focus of an earthquake by the value of the magnitude. The Richter scale is used to measure the magnitude of an earthquake, that is, the amount of energy released at the focus of the earthquake.

To calculate the magnitude of an earthquake, this scale is based on the maximum amplitude of the seismic waves (ground motions) recorded on a seismograph at 100 kilometers from the epicenter.

It is a logarithmic scale. This means that an increase of 1 point in magnitude corresponds to a 10-fold increase in the amplitude of the movement and a 30-fold increase in the energy released.
For example, the seismic waves of a magnitude 5 earthquake are ten times greater in amplitude than those of a magnitude 4 earthquake, and this earthquake releases about thirty times more energy.

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Definition: An Infrared radiation (IR) is an electromagnetic radiation with a wavelenght between 800 and 40 000 nm.
It was discovered by William Herschel in 1800.
It's composed of photons that transmit their energy to exposed objects and generating the agitation of their atoms.
This energy is felt as heat. In fact, everything that has a temperature above 0 Kelvin emits heat and so an infrared radiation.

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When stresses accumulate on a rock, it finally reaches its breaking point and suddenly releases the energy that has been previously accumulated, this is a seismic waves. They are differents types of waves :

- surface waves : only appears on the surface the earth

- body waves :
- primary (p-wave) : fastest waves because they can travel through liquids and solids. They are vibrating in the direction of the wave. There are longitudinal.

- secondary (s-wave) : slower, they can only travel through solids. Following an earthquake event, S-waves arrive at seismograph stations after the faster-moving P-waves and displace the ground perpendicular to the direction of propagation.