Marie Curie

Marie Curie discovered two new chemical elements – radium and polonium. She carried out the first research into the treatment of tumors with radiation, and she founded of the Curie Institutes, which are important medical research centers.

She is the only person who has ever won Nobel Prizes in both physics and chemistry.

Marie Curie’s Early Life and Education

Maria Salomea Sklodowska was born in Warsaw, Poland on November 7, 1867. At that time, Warsaw lay within the borders of the Russian Empire. Maria’s family wanted Poland to be an independent country.

Marie’s mother and father – Bronislawa and Wladyslaw – were both teachers and encouraged her interest in science.

When Marie was aged 10, her mother died. Marie started attending a boarding school, then moved to a gymnasium – a selective school for academically strong children. Aged 15, Marie graduated from high school, winning the gold medal for top student. She was passionate about science and wanted to continue learning about it.

Problems

Two obstacles stood in Marie’s way:

• her father had too little money to support her ambition to go to university
• higher education was not available for girls in Poland

Marie’s sister Bronya faced exactly the same problems.

To overcome the obstacles they faced, Marie agreed to work as a tutor and children’s governess to support Bronya financially. This allowed Bronya to go to France and study medicine in Paris.

For the next few years of her life, Marie worked to earn money for herself and Bronya. In the evenings, if she had time, she studied chemistry, physics, and mathematics textbooks. She also attended lectures and laboratory practicals at an illegal free “university” where Poles learned about Polish culture and practical science, both of which had been suppressed by the Russian Tsarist authorities.

In November 1891, aged 24, Marie followed Bronya to Paris. There she studied chemistry, mathematics, and physics at the Sorbonne, Paris’s most prestigious university. The course was, of course, taught in French, which Marie had to reach top speed in very quickly.

At first she shared an apartment with Bronya and Bronya’s husband, but the apartment lay an hour away from the university. Marie decided to rent a room in the Latin Quarter, closer to the Sorbonne.

This was a time of hardship for the young scientist; winters in her unheated apartment chilled her to the bone.

Top Student Again

In summer 1893, aged 26, Marie finished as top student in her master’s physics degree course. She was then awarded industrial funding to investigate how the composition of steel affected its magnetic properties. The idea was to find ways of making stronger magnets.

Her thirst for knowledge pushed her to continue with her education: she completed a master’s degree in chemistry in 1894, aged 27.

Homesick

For a long time, Marie had been homesick. She dearly wished to return to live in Poland. After working in Paris on steel magnets for a year, she vacationed in Poland, hoping to find work, but were no jobs for her.

A few years earlier she had been unable to study for a degree in her homeland because she was a woman. Now, for the same reason, she found she could not get a position at a university.

Back to Paris and Pierre

Marie decided to return to Paris and begin a Ph.D. degree in physics.

Back in Paris, in the year 1895, aged 28, she married Pierre Curie. Pierre had proposed to her before her journey back to Poland. Aged 36, he had only recently completed a Ph.D. in physics himself and had become a professor. He had written his Ph.D. thesis after years of delay, because Marie had encouraged him to.

Pierre was already a highly respected industrial scientist and inventor who, at the age of 21, had discovered piezoelectricity with his brother Jacques.

Pierre was also an expert in magnetism: he discovered the effect now called the Curie Point where a change of temperature has a large effect on a magnet’s properties.

Marie Curie’s Scientific Discoveries

The Ph.D. degree is a research based degree, and Marie Curie now began investigating the chemical element uranium.

Why Uranium?

In 1895, Wilhelm Roentgen had discovered mysterious X-rays, which could capture photographs of human bones beneath skin and muscle.

The following year, Henri Becquerel had discovered that rays emitted by uranium could pass through metal, but Becquerel’s rays were not X-rays.

Marie decided to investigate the rays from uranium – this was a new and very exciting field to work in. Discoveries came to her thick and fast. She discovered that:

• Uranium rays electrically charge the air they pass through. Such air can conduct electricity. Marie detected this using an electrometer Pierre and his brother invented.
• The number of rays coming from uranium depends only on the amount of uranium present – not the chemical form of the uranium. From this she theorized correctly that the rays came from within the uranium atoms and not from a chemical reaction.
• The uranium minerals pitchblende and torbernite have more of an effect on the conductivity of air than pure uranium does. She theorized correctly that these minerals must contain another chemical element, more active than uranium.
• The chemical element thorium emits rays in the same way as uranium. (Gerhard Carl Schmidt in Germany actually discovered this a few weeks before Marie Curie in 1898: she discovered it independently.)

By the summer of 1898, Marie’s husband Pierre had become as excited about her discoveries as Marie herself. He asked Marie if he could cooperate with her scientifically, and she welcomed him. By this time, they had a one-year old daughter Irene. Amazingly, 37 years later, Irene Curie herself would win the Nobel Prize in Chemistry.

Discovery of Polonium and Radium, and Coining a New Word

Marie and Pierre decided to hunt for the new element they suspected might be present in pitchblende. By the end of 1898, after laboriously processing tons of pitchblende, they announced the discovery of two new chemical elements which would soon take their place in Dmitri Mendeleev’s periodic table.

The first element they discovered was polonium, named by Marie to honor her homeland. They found polonium was 300 times more radioactive that uranium. They wrote:

“We thus believe that the substance that we have extracted from pitchblende contains a metal never known before, akin to bismuth in its analytic properties. If the existence of this new metal is confirmed, we suggest that it should be called polonium after the name of the country of origin of one of us.”

The second element the couple discovered was radium, which they named after the Latin word for ray. The Curies found radium is several million times more radioactive than uranium! They also found radium’s compounds are luminous and that radium is a source of heat, which it produces continuously without any chemical reaction taking place. Radium is always hotter than its surroundings.

Together they came up with a new word for the phenomenon they were observing: radioactivity. Radioactivity is produced by radioactive elements such as uranium, thorium, polonium and radium.

A Ph.D. and a Nobel Prize in Physics!

In June 1903, Marie Curie was awarded her Ph.D. by the Sorbonne.

Her examiners were of the view that she had made the greatest contribution to science ever found in a Ph.D. thesis.

Six months later, the newly qualified researcher was awarded the Nobel Prize in Physics!

She shared the prize with Pierre Curie and Henri Becquerel, the original discover of radioactivity.

The Nobel Committee were at first only going to give prizes to Pierre Curie and Henri Becquerel.

However, Pierre insisted that Marie must be honored.

So three people shared the prize for discoveries in the scientific field of radiation.

Marie Curie was the first woman to be awarded a Nobel Prize.

 

Amedeo Avogadro

                                 Lived 1776 – 1856.

Amedeo Avogadro is best known for his hypothesis that equal volumes of different gases contain an equal number of molecules, provided they are at the same temperature and pressure.

His hypothesis was rejected by other scientists. It only gained acceptance after his death. It is now called Avogadro’s law.

Avogadro was also the first scientist to realize that elements could exist in the form of molecules rather than as individual atoms.

Avogadro’s Life

Amedeo Avogadro was born in Turin, Italy, on August 9th, 1776.

His family background was aristocratic. His father, Filippo, was a magistrate and senator who had the title of Count. His mother was a noblewoman, Anna Vercellone of Biella.

Amedeo Avogadro inherited the title of Count from his father. In fact, Amedeo Avogadro’s full name was Count Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto – quite a mouthful!

Avogadro was highly intelligent. In 1796, when he was only 20, he was awarded a doctorate in canon law and began to practice as an ecclesiastical lawyer.

Although he had followed the family tradition by studying law, he gradually lost interest in legal matters. He found science was much more intellectually stimulating.

Mathematics and physics in particular attracted his logical mind. He spent increasing amounts of time studying these subjects. He was helped in this by the prominent mathematical physicist Professor Vassalli Eandi.

In 1803, in cooperation with his brother Felice, Avogadro published his first scientific paper, which looked at the electrical behavior of salt solutions. This was state-of-the-art science: only three years earlier, Avogadro’s fellow Italian Alessandro Volta had invented the electric battery.

In 1806, aged 30, Avogadro abandoned his successful legal practice and started teaching mathematics and physics at a high school in Turin. In 1809 he became a senior teacher at the College of Vercelli.

In 1820 Avogadro became professor of mathematical physics at the University of Turin. Unfortunately, this post was short lived because of political turmoil. Avogadro lost his job in 1823.

Avogadro was reappointed in 1833 and remained in this post until, at the age of 74, he retired in 1850.

Although he was an aristocrat, Avogadro was a down-to-earth, private man, who was quietly religious. He worked hard and his lifestyle was simple. His wife’s name was Felicita Mazzé. They married in 1818 when Avogadro was aged 42. They had six sons.

Avogadro’s Contributions to Science

In the early 1800s, scientists’ ideas about the particles we now call atoms and molecules were very limited and often incorrect. Avogadro was deeply interested in finding out how the basic particles of matter behave and come together to form chemical compounds.

He studied the work of two other scientists:

1. John Dalton
In 1808 John Dalton published his atomic theory proposing that all matter is made of atoms. He further stated that all atoms of an element are identical, and the atoms of different elements have different masses. In doing so, Dalton carried chemistry to a new level. But he also made mistakes about the way elements combine to form compounds. For example, he thought water was made of one hydrogen atom and one oxygen atom and wrote it as HO; today we know water contains two hydrogens to every oxygen and we write water as H20. Actually, Avogadro figured this out, as we shall see.

2. Joseph Gay-Lussac
In 1809 Joseph Gay-Lussac published his law of combining gas volumes. He had noticed that when two liters of hydrogen gas react with one liter of oxygen gas, they form two liters of gaseous water. All gases that he reacted seemed to react in simple volume ratios.

Avogadro’s Hypothesis

In 1811 Avogadro published a paper in Journal de Physique, the French Journal of Physics. He said that the best explanation for Gay-Lussac’s observations of gas reactions was that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules. This is now called Avogadro’s law. He published it when he was working as a physics teacher at the College of Vercelli.

In Avogadro’s (correct) view, the reason that two liters of hydrogen gas react with a liter of oxygen gas to form just two liters of gaseous water is that the volume decreases because the number of particles present decreases. Therefore the chemical reaction must be:

2H2 (gas) + O2 (gas) → 2H20 (gas)

In this reaction three particles (two hydrogen molecules and one oxygen molecule) come together to form two particles of water… or 200 particles react with 100 particles to form 200 particles… or 2 million particles react with 1 million particles to form 2 million particles… etc. The observable effect is that after the reaction, when all of the hydrogen and oxygen gases have become H20 gas, the volume of gas falls to two-thirds of the starting volume.

As a result of these observations Avogadro became the first scientist to realize that elements could exist as molecules rather than as individual atoms. For example, he recognized that the oxygen around us exists as a molecule in which two atoms of oxygen are linked.

 

André Marie Ampère

Lived 1775 – 1836.

André-Marie Ampère made the revolutionary discovery that a wire carrying electric current can attract or repel another wire next to it that’s also carrying electric current. The attraction is magnetic, but no magnets are necessary for the effect to be seen. He went on to formulate Ampere’s Law of electromagnetism and produced the best definition of electric current of his time.

Ampère also proposed the existence of a particle we now recognize as the electron, discovered the chemical element fluorine, and grouped elements by their properties over half a century before Dmitri Mendeleev produced his periodic table.

The SI unit of electric current, the ampere, is named in his honor.

Beginnings

André-Marie Ampère was born into a well-to-do family in the city of Lyon, France, on January 20, 1775. His father was Jean-Jacques Ampère, a businessman; his mother was Jeanne Antoinette Desutières-Sarcey, the orphaned daughter of a silk-merchant. André-Marie’s parents already had a daughter, Antoinette, born two years before André-Marie.

It was an intellectually exciting period in French history; Antoine Lavoisier was revolutionizing chemistry; and Voltaire and Jean-Jacques Rousseau, the leaders of the French Enlightenment, were urging that society should be founded on science, logic, and reason rather than the religious teachings of the Catholic Church.

When André-Marie was five years old, his family moved to a country estate near the village of Poleymieux about six miles (10 km) from Lyon. His father had grown so wealthy that he no longer needed to spend much time in the city. A second daughter Josephine was born when André-Marie was eight.

An Unusual Education
The education André-Marie received was rather unusual. His father was a great admirer of Jean-Jacques Rousseau, one of the leaders of the French Enlightenment. He decided to follow Rousseau’s approach for André-Marie’s education. This meant no formal lessons.

André-Marie could do as he pleased, learning about anything he felt like. He was also allowed to read anything he wanted to from his father’s large library. A recipe for disaster, you may think? In fact, it worked! And it worked exceptionally well. André-Marie developed an insatiable thirst for knowledge, going as far as learning entire pages of an encyclopedia by heart.

Although a child of the French Enlightenment, André-Marie did not reject the church, and he remained a practicing Catholic throughout his life.

“My father… never required me to study anything, but he knew how to inspire in me a great desire for knowledge. Before learning to read, my greatest pleasure was to listen to passages from Buffon’s natural history. I constantly requested him to read me the history of animals and birds…”

 

Mathematics
Aged 13, André-Marie began a serious study of mathematics using books in his father’s library. He submitted a paper about conic sections to the Academy of Lyon, but it was rejected.

The rejection spurred him into working harder than ever. His father bought him specialist books to help him improve. He also took his son into Lyon, where Abbot Daburon gave him lessons in calculus – the first formal lessons André-Marie ever had.

Physics
Having taken his son for formal mathematics lessons, his father also took him to Lyon’s college to attend some physics lectures, which resulted in André-Marie beginning to read physics books as well as mathematics books.

Revolution Followed by Tragedies
Life so far had been peaceful and enjoyable for André-Marie, but a period of tragedy was beginning to unfold.

In 1789, when André-Marie was 14, the French Revolution began.

In 1791, while André-Marie continued his home-studies on their country estate, the revolutionaries gave his father the legal role of Justice of the Peace.

In 1792, André-Marie’s older sister Antoinette died.

In 1793, the Jacobin faction of the revolution guillotined his father. (The great chemist Antoine Lavoisier was guillotined by revolutionaries in 1794.)

Mercifully, André-Marie, studying mathematics and science on the family estate, survived the revolution’s reign of terror. He was devastated by his father’s death and abandoned his studies for a year.

Becoming a Mathematician and Scientist

In late 1797, aged 22, André-Marie Ampère opened up shop as a private mathematics tutor in Lyon. He proved to be an excellent tutor, and soon students were flocking to him for help.

His tutoring work came to the attention of Lyon’s intellectuals, who were impressed by Ampère’s knowledge and his enthusiasm.

In 1802, he became a school teacher in the town of Bourg 40 miles (60 km) from Lyon. A year later he returned to Lyon to work in another teaching position.

In 1804, he moved to the French capital, Paris, tutoring university level classes at the École Polytechnique. His work impressed other mathematicians so much that he was promoted to full professor of mathematics in 1809, despite having no formal qualifications.

André-Marie Ampère’s Contributions to Science

Electromagnetism and Electrodynamics

In 1800, while Ampère worked as a private tutor in Lyon, Alessandro Volta had invented the electric battery. One result of this was that for the first time ever, scientists could produce a steady electric current.

In April 1820, Hans Christian Oersted discovered that a flow of electric current in a wire could deflect a nearby magnetic compass needle. Oersted had discovered a link between electricity and magnetism – electromagnetism.

In September 1820, François Arago demonstrated Oersted’s electromagnetic effect to France’s scientific elite at the French Academy in Paris. Ampère was present, having been elected to the Academy in 1814.

Ampère was fascinated by Oersted’s discovery and decided he would try to understand why electric current produced a magnetic effect.

The Electron

To explain the relationship between electricity and magnetism, Ampère proposed the existence of a new particle responsible for both of these phenomena – the electrodynamic molecule, a microscopic charged particle we can think of as a prototype of the electron. Ampère correctly believed that huge numbers of these electrodynamic molecules were moving in electric conductors, causing electric and magnetic phenomena.

Discovery of Fluorine

Ampère did not restrict his interests to mathematics and physics; they were wide ranging and included philosophy and astronomy. He was particularly interested in chemistry. In fact, preceding his work in electromagnetism, he made significant contributions to chemistry.

Ampère discovered and named the element fluorine. In 1810, he proposed that the compound we now call hydrogen fluoride consisted of hydrogen and a new element: the new element had similar properties to chlorine he said. He and Humphry Davy, who was British, entered into correspondence (even though France and Britain were at war). Ampère proposed that fluorine could be isolated by electrolysis, which Davy had previously used to discover elements such as sodium and potassium.

It was only in 1886 that French chemist Henri Moissan finally isolated fluorine. He achieved this using electrolysis, the method Ampère had recommended.

Black holes

Black holes

 Black holes are areas in the universe where gravity pulls in everything, even light. Nothing can get out and all objects are squeezed into a tiny space.  Because there is no light in black holes we cannot see them.  But scientists can detect the immense gravity and radiation around them. They are the most mysterious objects in astronomy. Scientists think that the first black holes were formed when the universe began about 13 billion of years ago.

Albert Einstein was the first scientist to predict that black holes existed. But it was in 1971 that the first black hole was actually discovered.

Black holes can have various sizes, some may be even as small as an atom. But they all have one thing in common – a very large mass.

There are three kinds of black holes :

A stellar occurs when very large stars burn away the rest of the fuel that they have and collapse. It is so massive that several of our suns could fit in it. Our sun, however, could never become a stellar because it is too small.

Supermassives are the largest and most dominating black holes in our universe. They have masses of a million or more suns put together. Every galaxy has a supermassive in its centre. As they become larger and larger they pull in more material. The black hole at the centre of our Milky Way is four million times as massive as our sun and surrounded by very hot gas.

Intermediate mass black holes have not been found yet, but scientists think they probably exist. They have the mass of between a hundred and a thousand suns.  

 A black hole consists of three parts:

The outer event horizon is the farthest away from the centre. Gravity here is not so strong and you would be able to escape from it.

The inner event horizon is the middle part of a black hole. In this area an object would be slowly pulled to the centre.

The singularity is the centre of a black hole, where gravity is strongest.

Madnets and magnetism.

Madnets and magnetism.

 A magnet is a piece of rock or metal that can pull other metals towards it. The force of magnets is called magnetism. Together with gravity and electricity it is a basic force of nature. Early humans discovered magnets and magnetism thousands of years ago. They found out that certain types of rock, called loadstone, pulled iron and other metal objects towards it. After some time they found out that thin pieces of such a rock would always point in one direction if you hung it on a piece of thread . The ends of such a metal are the poles of a magnet. All magnets have a magnetic field around them, the force between the two poles.

Magnets attract or repel other metals. This is because every magnet has two poles: a north and a south pole. North and south poles attract each other but two north poles or two south poles push each other apart.

Our planet is also a big magnet with a North and a South Pole. But the Earth’s magnetic poles are not in the same place as the geographic poles. The magnetic North Pole, for example, is in northern Canada. Compasses always point to the magnetic poles, not to the geographic ones.

Magnetism comes from electrons , the tiny particles that fly around the nucleus of an atom. They are negatively charged and produce a very weak magnetic field. When many of these electrons point towards the same direction they can pull metals to them.

It is also possible to make a magnet by taking an existing one and rubbing another piece of metal with it. If you keep rubbing the new piece of metal in the same direction its electrons will start to point in that direction , thus creating a new magnet.

If a magnet keeps its magnetic field all the time we call it a permanent magnet. However , not all magnets are permanent . Some objects become magnets only when electricity passes through them. They are called electromagnets. There are many examples of such electromagnets in everyday life: car motors, railway signals, loudspeakers .

Magnetism and electricity

In the 1700s scientists discovered that magnetism and electricity had similar features. Just like magnets have two poles, electricity has positive and negative charges . A positive and a negative charge attract each other and two negative or two positive charges repel each other.

After they had found this out they started making useful tools and machines with the help of electricity and magnetism. The Danish physicist Oersted sent electricity through a wire and put a compass near it. To his surprise the compass needle moved. Soon after that the first electromagnet was made by making a wire into a coil and sending electricity through it.

Use of magnets

The first magnetic instruments were compasses which sailors used to guide them on their journeys . Today, magnets can be found in many areas of everyday life. They are in washing machines, hold doors shut and work in generators and electric motors. Credit cards have magnetic strips on them that give you financial information. Magnetic audio and videotapes as well as disks have many tiny magnetic particles which are used to store sounds, pictures and other information.

In medicine a magnetic resonance imaging machine (MRI) can create exact pictures of organs and bones inside the human body . It is much better and more exact than x-rays .

Powerful electromagnets are attached to big cranes that can move iron and steel. In some parts of the world trains travel on tracks that are magnetized . These trains, called maglev, are lifted above the tracks and do not have any contact with them. They travel at speeds of up to 480 km an hour.

Magnets in animals

Scientists have also discovered that some animals, like pigeons , dolphins and turtles may have some magnetic particles in their body. They are able to detect the Earth’s magnetic field and find out their location.

 

 

X-rays

X-rays

 X-rays are high energy waves that are invisible. They are useful because they can pass through many things that normal light cannot. For example, doctors can see inside the human body and security guards at airports can see inside your handba

Discovery

In 1895, a German scientist, Wilhelm Roentgen, discovered X-rays by accident. He called them X-rays because he hadn’t seen such a form of energy before. In mathematics X means something unknown. Roentgen took his first X-ray pictures of the bones of his hand. In 1901 he received the first Nobel Prize for Physics for his discovery.

X-Rays in Medicine

X-rays are valuable in medicine because they can see through certain parts of the body. Doctors can take pictures of bones, teeth and tissue. They use these pictures to see which bones are broken or to find out which teeth have holes in them.

To produce X-ray pictures you need two things: a special plate that can capture X-rays is placed behind a part of a person’s body. A machine that produces X-rays is put in front of the person.

The X-rays are strong enough to pass through the skin and muscles but they cannot pass through hard objects like bones. In the picture you see hard objects, like bones, as white areas. Objects that X-rays go through are dark.

There are some situations in which X-rays cannot give you a clear picture. Some organs, for example, may block X-rays from showing a broken bone. For this reason computed tomography (CT) was invented. A person is put inside a scanner, which is a large tube-shaped machine. Then he is X-rayed from all sides. A computer puts together all of these images and can show doctors more than a normal X-ray can. CTs are used for brain diseases and head injuries.

X-rays, however, can also do harm to your body. Patients must wear special protection for the parts of their body that are not X-rayed. Doctors and helpers who work with X-ray machines must wear lead aprons and stand behind screens.

X-rays are sometimes used to in the fight against cancer. Doctors often beam X-rays at cancer cells in order to destroy them.

X-rays in science

Scientists often use X-rays to study the structure of other organisms or minerals that are in rock. By bombarding material with X-rays you can tell how old an object is.

Since the 1970s X-rays have been used to study stars and galaxies that are very far away. X-ray telescopes are put on board satellites that orbit far above the earth’s surface. They can see things that telescopes on earth cannot detect, because X-rays are absorbed by the earth’s atmosphere.

Other uses

Factories use X-rays to find cracks in machines or in metal objects. At airports X-ray machines scan millions of handbags and suitcases for weapons like bombs, guns or knives.

Earthquakes

 Earthquakes

An earthquake is one of the worst natural disasters on our earth. We think that the ground we stand on is very stable, but it isn’t. It moves quite a lot. In the last few decades scientists have been able to find out why earthquakes happen.

Earthquakes happen when there is a sudden vibration in the earth’s crust. It’s like a large lorry that travels down your street. When it passes by, you feel your house shake.

Earthquakes can be caused by a lot of things :

Volcanoes that suddenly erupt

Meteorites that hit the earth

Undergrounds explosions

Buildings that fall apart

 But most earthquakes happen because the earth’s plates move.

In the middle of the 20th century scientists found out that continents do not always stay in the same place. They have been moving on plates for millions of years. The earth’s surface is made up of many such plates. Where two plates meet magma comes out of the inner part of the earth . These areas are called faults—breaks in the earth’s crust.

How plates move

When two plates move away from each other lava or magma comes out of the earth. Most of this happens at the bottom of oceans, where the earth’s crust is very thin. Lava cools down when it reaches the water and underwater mountains are formed.

When plates push towards each other—one of them slides under the other. Rocks are pushed up and new mountains are formed.

Some plates slide past each other— for example, one moves north and the other moves south . When these plates move along faults a lot of energy is released and the biggest earthquakes happen.

We only hear about earthquakes once in a while , but they really happen every day. There are more than 3 million earthquakes every year—about 8,000 every day or one every 11 seconds.

But most of them are very weak or they happen in places where nobody lives. Some of them take place on the sea floor.

Where do earthquakes happen ?

 Earthquakes occur all over the world but there are places where they happen more often. Big earthquakes can be found where plates meet.

80% of the world’s earthquakes happen around the Pacific Ocean—near the east coast of Asia and the west coast of America. Japan has over 2,000 earthquakes every year and California and South America are also very active earthquake zones. The edge of the Pacific Ocean is also called the “Ring of Fire” because there are also many active volcanoes in this region.

Earthquake Waves

When there is a sudden movement in the earth’s crust, energy moves in the form of waves . It’s like dropping something into water.

Body waves move through the inner part of the earth and surface waves travel over the earth’s surface.

Body waves can travel very fast—up to 8 km a second. They travel through rock , water and gas . When they reach other places on the earth’s surface they can be registered there. They are usually the first waves to get to the surface.

Surface waves cause the most damage, but they move very slowly. These waves come at the end of an earthquake.

Man-made Earthquakes

Sometimes people can make earthquakes happen. They can fill man-made lakes with water after building a dam—or they test atomic bombs underground. Some of these tests can help scientists find out how quakes happen.

How earthquakes are measured

With a machine called a seismograph scientists can tell where an earthquake happened and how strong it was.

The place in the earth where the movement takes place is called the focus or hypocentre. From here, waves start to spread out in all directions. This focus can be very near to the surface or it can be hundreds of km below it. The area on the surface exactly above the focus is called the epicentre. This is the place where the waves hit first and where the most damage is done.

Whenever an earthquake hits us you hear how powerful it is. The Richter Scale is used to rate the magnitude of earthquakes. Small quakes have a rating of under 4. You won’t see a lot of damage here. Medium-sized earthquakes reach between 5 and 7 on the scale, and the really big ones are above 7. The largest earthquake that has ever been registered was at 9.5 on the Richter scale.

There are more than 100 seismograph stations all over the world. When the earth shakes seismologists compare the information they get and then they can tell where the earthquake really happened.

Effects of earthquakes

Earthquakes make the ground move. Buildings shake and many of them collapse. Landslides also happen when rocks get loose.

Another danger is fire. In 1906 San Francisco was hit by a big earthquake and many houses burned down because they were made of wood.

When an earthquake occurs on the sea floor, big waves - called tsunamis—hit the coast. They often come without any warning and they kill many people and destroy buildings and streets near the coast.

Earthquakes also can lead to diseases, especially in developing countries. When water supplies are destroyed people don’t have safe water to drink. Sometimes earthquakes also hit hospitals where injured people are treated.

Dealing with earthquakes

We understand earthquakes a lot better today than we did 50 years ago, but we still can’t do very much about them. They are so powerful, that we cannot control them.

Scientists can tell us in which regions earthquakes will probably happen, but they can’t tell us exactly where.

So what can we do about earthquakes? We can make our houses we live in and buildings we work in safer. Today architects use materials that won’t collapse when an earthquake hits—like steel and concrete.