Roaming the Oceans

Roaming the Oceans

When anything tries to move through water, the water resists its movement. Boat designers try to minimize water resistance, called “drag”, by making boat hulls as smooth and streamlined as possible. Water underneath a boat pushes up against its hull with a force called “upthrust”. If the force of the boat's weight is equal to the upthrust of the water, the boat floats. If the boat weighs more than the upthrust of the water, it sinks. A submarine, or a smaller underwater craft called a submersible, sinks under the waves by letting water into its ballast tanks to make it heavier. It rises to the surface again by forcing the water out of the tanks with compressed air, or by dropping heavy weights to make the craft lighter. Most working boats, submarines and submersibles are powered by propellers with angles blades that push against the water as they turn.

Setting Sail

A sail is set at an angle so that wind blowing around the sail from the side reduces the air pressure in front of it, sucking the sail and the boat forward. This means that a sail can use a wind blowing in one direction to propel a yacht in a completely different direction. But a yacht can never sail directly into the wind.

When compasses were first used on ships, seamen did not understand how they worked and were afraid of the magical powers they seemed to possess. Compasses were hidden from the crew inside a box called a binnacle.

Manipulator Arm

A robot arm with a mechanical claw at the end of it picks up objects from the sea bed.

Below the Surface

Submersibles allow scientists to explore the sea bed, study living organisms in their natural surrounding and investigate shipwrecks.

Ocean. Photo by Elena.

Crew Sphere

The crew members sit inside a metal sphere because a sphere is the best shape to resist the crushing pressure of water. Air for the crew to breathe is also stored in spherical tanks.

Global Positioning System (GPS)

Navigators used to figure out the position of a ship at sea by studying the position of the sun or the stars. Now they use a system called Global Positioning System or GPS. Satellites orbiting the Earth send out radio signals that are picked up by a receiver in the ship. The signals tell the receiver where each satellite is, how fast it is flying, in which direction and what the time is. By using signals from at least three satellites, the receiver can calculate the position of the ship.

Thruster

A thruster is a propeller inside a tube driven by an electric motor. Submersibles are propelled and sterred by thrusters.

Ballast tanks

The submersible sinks by letting water into its ballast tanks.

Batteries

Electric power for the thrusters, lights, cameras and other instruments is supplied by a set of batteries.

Iron ballast

Iron bars provide some of the weight that is required to sink the submersible.

God-Kings of Egypt

The God-Kings

An ancient Egyptian creation myth tells how the god Osiris was sent by Re, the sun-god, to rule the country. The Egyptian believed that all pharaohs were god kings. The god-kings took part in many ceremonies. They had to dress, eat and even wash in a special way, and every day they went to the temple to offer food to their ancestors. People expected pharaohs to be physically strong, expert at hunting and able to lead the army to victory in battle. Their subjects thought the god-kings controlled the flowing and flooding of the Nile and the growth of crops, as well as the country's success in foreign trade. Everyone knelt and kissed the ground when they approached the royal person. The pharaohs continued to be worshiped even after they had died and joined the god Osiris in the kingdom of the dead.

Make of a pharaoh

Oval shapes containing hieroglyphs were called cartouches. Two of them make up a pharaoh's name. Cartouches have helped Egyptologists decipher the ancient Egyptian language.

The Great Royal Wife

Pharaohs' wives were also regarded as gods, and shared their husbands' wealth. A painted limestone bust of Queen Nefertiti shows her wearing a crown and necklace rich with jewels. Nefertiti was the wife of Akhenaten.  She helped him establish a new city at Amarna on the east bank of the River Nile in Middle Egypt. Women rarely ruled the country unless it was for a short time at the end of the dynasty when there were no men to take over Hatshepsut was the only strong woman ruler.

God-Kings of Ancient Egypt. Photo by Elena.

Did You Know?

When Queen Hutshepsut's husband died, she took over government and ruled for her stepson Tuthmosis III, who was only five. She held power for about 20 years. Statues show her wearing the false beard of kingship.

Court Visitors

Foreigners, such as this group from the Middle East, often appeared at the pharaoh's court. They came to offer gifts or to discuss trade agreement.

Choice of Crowns

Pharaohs might wear the white crown of Upper Egypt, the red crown of Lower Egypt, the double crown of a united Egypt, the atef crown of Osiris or the blue crown. There ar white crown, red crown, double crown, blue crown and atef crown. 

Comfort at Court

Slaves fanned the pharaohs and his wife on their comfortable cushioned thrones. The king held a crook and flail – symbols of power linking him to the god Osiris. He also wore a crown and a false beard.

Royal seat

Tutankhamun's wooden throne, covered in gold leaf, pictured the young king with his wife Ankhsensmon. 

Messages from Space

Messages from Space

Satellites circling the Earth send us pictures of the weather and relay telephone calls and television programs around the world. They also study vast areas of the Earth and its oceans, taking photographs and measurements with their cameras and instruments and beaming them down to Earth by radio. Some satellites circle the planet from pole to pole; others circle around the equator. Most satellites orbit the Earth at a height of between 124 miles and 496 miles and have to travel at a speed of 5 miles per second to stay in orbit.

Communications and weather satellites are boosted to a height of 22,320 miles (36,000 km) – much higher that other satellites. At this height above the equator, a satellite circles the Earth once every 24 hours, the same time the Earth takes the spin once on its axis. This kind of orbit is called  “geostationary” because the satellite seems to hover over the same spot on Earth. It takes three satellites in geostationary orbit to relay telephone calls between any two points on Earth.

Communications Satellites

A communications satellite or comsat, works a little like a mirror on the sky, it receives radio signals beamed up to it from Earth, amplifies them and sends them back to a different place on Earth.

A Live Broadcast

Satellites enable events such as the Olympic Games to be watched anywhere in the world seconds after the happen.

In the Sky

A low-flying satellite orbits at a height of about 155-186 miles just outside most of the Earth's atmosphere. It can dip down to as low as 74 miles to take close-up photographs of interesting places. Its advanced camera systems can see details as small as 2 inches across.

Messages from Space. Photograph by Elena.

Gas Tanks

The satellite uses jets of gas from its gas tanks to stop it from drifting out of position.

Communications Circuits

The satellite's communications circuits can relay tens of thousands of telephone calls at the same time.

Picturing the Weather

Satellite pictures can help a weather forecaster see how weather systems, such as cyclones, grow and move across the oceans. Views from the space would be impossible to obtain from the ground.

Weather Satellite's

The world's weather constantly changes, and the temperature of the sea, the land and the clouds vary all the time. A weather satellite carries heat-sensitive cameras that continually monitor the weather.

Staying on Orbit

If could throw a ball hard enough, it would fly all the way around the Earth, because the curve of its fall would exactly match the curve of the Earth's surface. To see this in action, make two plastic balls – one 2 in across to represent gravity, and one ¾ in across to to represent a satellite. Thread 20 in of string through a thread spool (Earth), and tie each end to a key. Push each key into one of the balls. Hold the thread spool and the large ball and start the small ball spinning. Let the large ball go. The satellite tries to fly away from Earth but gravity pulls it back. When the two forces are balanced, the satellite orbits Earth.

Messages from Space. Illustration by Elena.

Ancient Egypt: A Royal Journey

Power of the Pharaohs

The civilization we call ancient Egypt started about 5,000 years ago, when the rule of the pharaohs began. They made Egypt a rich and powerful nation, admired throughout the ancient world. They also ordered the building of great temples for their gods and elaborate tombs for themselves. Some pharaohs, such as Pepy II, came to the throne when they were very young and stayed in power for many years.

Sons inherited their father's throne. Pharaohs' wives were also important, but few women ever ruled the country. Teams of workers crafted beautiful objects for the pharaohs and their families. They used materials such as semi-precious stones and gold from the desert mines. The royal couple often displayed their riches in public. Processions, receptions for foreign visitors and visits to the temples were opportunities to show the power of the pharaohs.

A Royal Journey

The magnificent royal barge gliding down the river reminded people of the wealth and importance of their god-king and his “Great Royal Wife”.Safe landing: Oarsmen were skilled at bringing the boat smoothly to rest beside the dock.

Fit for a pharaoh: A sphinx guarded the prow. The rest of the barge was covered with gold and inlaid with semi-precious stones.

People in waiting: Officials and tribute bearers, soldiers and slaves stood by the immense columns of the temple to welcome their pharaohs.

Pharaohs. Photo by Elena.

The Dynasties of the Pharaohs

Archaic Period, 2920 BC to 2575 BC.: Upper and Lower Egypt were united. Building programs included impressive monuments in Saqqara and Abydos. Stone vases.

Old Kingdom, 2575 BC to 2134 BC.: This period was also known as the Age of Pyramids. Crafts and architecture developed. Picture symbols, called hieroglyphs, were used to write the texts inside the pyramids. Figures of female brewer.

First Intermediate Period, 2134 BC to 2040 BC.: At the end of the sixth dynasty, a series of weak pharaohs ruled. Local officials called nomarchs struggled for more power. Low Nile floods caused widespread famine.

Middle Kingdom. 2040 BC to 1640 BC.: Strong pharaohs united the country again and trade revived. The twelfth-dynasty pharaohs organized canals and reservoirs for better irrigation, King Mentuhotpe II.

Second Intermediate Period, 1640 BC – 1550 BC.: The pharaohs lost control. The Hyksos from the Near Est settled in the delta region.

New Kingdom, 1550 BC to 1070 BC.: Ahmose ousted the Hyksos. The pharaohs who followed him expanded Egypt's frontiers to form an empire.

Third Intermediate period, 1070 BC to 712 BC.: Power was divided between the pharaohs and the high priests.

Late Period, 712 BC to 332 BC.: The Egyptian conquerors became the conquered. Successive invasions of Nubians, Assyrians and Persians took over Egypt. In 332 BC, Alexander the Great freed Egypt from Persion rule.

Harnessing the Sun

Harnessing the Sun

The sun is an extraordinary powerful form of energy. In fact, the Earth receives 20,000 times more energy from the sun than we currently use. If we used much more of this source of heat and light, it could supply all the power needed throughout the world. We can harness energy from the sun, called “solar energy”, in many ways. Satellites in space have large panels covered with solar cells that change sunlight directly into electrical power.

Some buildings have solar collectors that use solar energy to heat water. These panels are covered with glass and are painted black inside to absorb as much heat as possible. Some electric cars are even powered by solar panels. Solar energy is a clean fuel, but fossil fuels, such as oil or coal, release harmful substances into the air when they are burned. Fossil fuels will run out eventually, but solar energy will continue to reach the Earth long after the last coal has been mined and the last oil well has run dry.

Saving energy

An energy-efficient house is designed to minimize energy waste. It generates its own electricity, but it is still connected to the national power grid. If it generates more electricity than it needs, the excess is supplied to the grid. If it needs more electricity, this supplied by the grid.

Keeping warm

Most of the heat lost by a house escapes through the roof. The roof of an energy-efficient house is lined with insulation material to stop heat from escaping.

Solar panels

When the sun shines on a solar panel, solar energy is converted into electricity to power electrical appliances in the house, such as water heaters or cooling fans.

The Sunny Side

Many houses are built today with one long side facing the sun so that it can absorb as much solar energy as possible during the day.

Harnessing the Sun. Photo by Elena.

Small windows

Windows that do not face the sun are smaller, to reduce heat loss.

Water tanks

Hot water from the roof-top solar collectors is stored in tanks for later use. The tanks are insulated to stop the heat from escaping.

Cover Up

Awning shield windows from the excessive heat and glare of the sun.

Skylights

These let in natural light and can be opened to let war air escape.

Walls

The walls are filled with insulating materials to stop heat from escaping through them.

Large Windows

Windows facing the sun are large so that plenty of solar energy can pass through and warm the rooms inside. In the evening, when the sun sets, heavy curtains or shutters are closed over the windows to stop the heat from escaping.

Warming Up

Greenhouse are made of glass and have slanted roofs to allow the maximum amount of sunlight to enter. The sun's heat is trapped inside, which raises the temperature inside the greenhouse and helps the plants to grow. Plants in a greenhouse can be grown all year around.

Solar Cells

Solar cells convert light directly into electricity. Light reaches the cell through a transparent protective coating. The first layer is made from a material called N-type silicon (silicon is one of the most plentiful elements in the Earth's crust). N-type silicon is specially treated so that it has more electrons than normal silicon. This has gaps in its structure because it has less electrons. Sunlight gives electrons enough energy to jump from the N-type silicon to the P-type to fill the gaps. When electrons move, they make an electric current. The tiny currents made by hundreds of thousands of solar cells are added together to make an electric current that is large enough to power equipment.