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.

 

 

Isaac Newton - AGreat Scientist

Isaac Newton - AGreat Scientist

 Isaac Newton was one of the world's greatest scientists. He did research in mathematics, physics, astronomy and many other fields.

Newton was born in 1642. He worked on his family’s farm but was not really interested in farming. His father died before Isaac was born. In his childhood he spent much time with his grandmother. Newton didn’t have many friends and never married.

Newton did most of his scientific work at Cambridge, where he was a professor for many years. Although some other scientists criticized his work, he was admired throughout Europe. Queen Anne made Newton a knight. He died in 1727 and was buried at Westminster Abbey in London. 

Isaac Newton was very ambitious young scientist who carried out his experiments very accurately. His main theory was that everything in nature could be explained through mathematics. Not all scientists had the same opinion.

Newton was an astronomer, who studied the Earth, the planets and stars. He became well-known for theories of gravity, in which he claimed that all objects of the universe have a gravitational force that pulled other objects towards them. An apple is pulled to the Earth's surface just like the Earth is being pulled towards the sun. He also showed that planets move around the sun in ellipses. His theory of gravity dominated physics for some time.

He also conducted experiments with light and found out that normal light is made up of many colors. He used prisms to break up light into a rainbow of colors. Newton invented a new kind of telescope that used lenses. It made objects look bigger.

In his book “The Mathematical Principles” Newton describes the three laws of motion:

Every moving object keeps moving until something stops it. An object that lies on the ground continues to lie there until a force sets it in motion.

Acceleration happens when a force acts on a mass. The greater the mass the more force must be applied to move the object. For example, you need more force to push a car than you need to push a bike.

For every action there is an equal and opposite reaction. A rocket, for example, pushes down on the ground with its engines; the opposite action moves the rocket into the sky.

These principles were very difficult to understand at that time. Only few people really knew what Newton meant.

Newton also devoted a great deal of his life to alchemy. He studied it closely and believed that he was a special person who had magic powers and secret wisdom to change substances and objects. Newton wanted to keep these studies to himself; therefore he did not publish any of his alchemist works. At that time alchemy was a much-discussed topic that not everyone accepted.

Although Newton was one of the great scientists of his time, he based his work on the discoveries of Galileo and other scientists who lived before him. Scientists of following generations admired Newton's work. Albert Einstein, 20 th century scientist, thought highly of Newton’s work although his theory of general relativity moved away from his ideas.

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 handbag.

                                                          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.