Bringing a rock uphill increases its potential energy under gravity. Stretching a rubber band increases its elastic potential energy, which is a form of electric potential energy. A mixture of a fuel and an oxidant has a chemical potential energy, which is another form of electric potential energy. Batteries too have chemical potential energy.
There are various types of potential energy, each associated with a particular type of force.
Gravitational potential energy is experienced by an object when height and mass is a factor in the system. Gravitational potential energy causes objects to move towards each other.
If an object is lifted a certain distance from the surface from the Earth, the force experienced is caused by weight and height.
Work is defined as force over a distance, and work is another word for energy. The potential energy added when you lift an object is:
or
Here, formula_5 is the acceleration due to gravity.
The total work done by gravitational potential energy when an object falls from position 1 to position 2 is:
or
Electric potential energy is experienced by charges both different and alike, as they repel or attract each other. Charges can either be positive (+) or negative (-), where opposite charges attract and similar charges repel.
If two charges were placed a certain distance away from each other, the potential energy stored between the charges can be calculated by:
Elastic potential energy is experienced when a rubbery material is pulled away or pushed together. A spring for example stores elastic potential energy. The amount of potential energy the material has depends on the distance pulled or pushed. The longer the distance pushed, the greater the elastic potential energy the material has.
If a material is pulled or pushed, the potential energy can be calculated by:
Ship
A ship is a large vehicle used to travel on water. It is bigger than a boat. Most are cargo ships, which carry most of the world's international trade. There are also many warships, passenger ships and other kinds for different purposes.
When people talk about a ship, they often use the pronoun "she". For example: She was launched on 29 December 1878.
The first ships used oars or the wind (or both) to make them move.
From about 4000 BC the Ancient Egyptians were making wooden sail boats. By 1200 BC the Phoenicians and Greeks had begun to make bigger sailing ships which were about 30 metres (100 feet) long and could carry 90180 tonnes of cargo. The Romans made even bigger ships which could carry up to 1,000 people and 1,000 tonnes of cargo. The 8th century saw the rise of the Vikings, who were famous for their "longships" and which were mainly used for raiding other countries, but also for trading. The longships had flat bottoms so they could move in shallow (not deep) rivers.
Sailing ships were used for thousands of years, but they were very important from the Age of Discovery to the 19th century. The Chinese admiral Zheng He commanded a fleet of large 'treasure ships' on seven voyages all over Asia up to East-Africa in the early fifteenth century. The most successful and largest fleet in the 17th century was the Dutch fleet (see the Netherlands). For trade and transport the Dutch often used a particular kind of trading ship, called a flute ("fluyt" in Dutch). Transport of people and cargo on sailing ships became rare in the early 20th century.
Some famous ships from this era include:
In the 19th century, steamboats became commonplace.
At one time, the steamships "Titanic", "Olympic", and "Britannic" were the largest ships in the world, "Titanic" sank on her maiden voyage after hitting an iceberg, becoming one of the most famous shipwrecks of all time, the "Olympic" was "Titanic" 's nearly identical twin, and actually set sail before "Titanic" and was scrapped in the 1930s after a very successful career including her being a passenger liner and a warship in World War I. The "Britannic" was the largest of these three sister ships, and was supposed to be more grand and elegant than the "Titanic", but before she set sail on her maiden voyage, WWI broke out and she was stripped of her elegant furniture and elaborate paneling and became a hospital ship. During her term as a hospital ship, she was sunk by either a mine or torpedo, no one knows for sure. The "Titanic" lies at the bottom of the North Atlantic Ocean, off the coast of Nova Scotia, and the "Britannic" lies in the Aegean Sea, off the coast of the Island of Kea.
After World War II ships with diesel engines became commonplace. Passenger airliners replaced passenger ships for long trips in the late 20th century. Cargo ships became much bigger. The main kinds are container ships for mostly manufactured goods, and bulk carriers including oil tankers.
The world's largest ship is the "Prelude", owned by Shell. It is being built on Geoje Island, South Korea. It is 488m long and has the internal capacity greater than the total volume of four large aircraft carriers. What it will do is collect natural gas off the coast of Australia, and liquify it. When liquified, the hydrocarbon takes up 600 times less space than its gas. Smaller tankers will take the liquid gas to its buyers. The ship will do liquifying and temporary storage, which is usually done on land. Shell believes this justifies the cost of the ship.
The shipping yard builds all kinds of structures for the oil industry. It employs 30,000 workers.
Boat
A boat is a vehicle used to travel on water. It is smaller than a ship and can be lifted out of the water and carried on a ship. Some boats have sails, some are powered by rowing with oars, and some use motors. Those that use steam engines are steamboats
These boats are usually made of wood. However, some parts are made of metals like steel and aluminium. Expensive boats may have parts from fiberglass or composite materials and some even have helicopter pads. There are some boats that can even go underwater. They are called submarines.
A narrowboat is a boat designed to be used on narrow canals. It is sometimes called a barge.
The Pesse Canoe is likely the oldest boat recovered to date as it was built sometime around 8,000 BCE
Navy
The navian is the part of a country's military that fights on water using boats. People in the navy are called navians. The navy is mostly made up of warships. It may also have its own air force and soldiers. It may have special boats that can go underwater, called submarines, or another kind of special boat that is meant to carry airplanes, called aircraft carriers.
Originally, Naval war was fought by ramming other ships and then jumping onto them to fight the crew. In Ancient Greece and Rome, the ships were usually powered by oars. During the Middle Ages, the cannon was invented. These could be shot at other ships from a great distance. Warships around this time also began to use sails instead of oars for power. In the middle 19th century, ships began to be plated in armor for protection. Steam engines allowed them move while carrying the armor, and better ones soon made them much faster. These early warships, called ironclads, are thought to have begun the type of Naval warfare used today. Ships soon became much larger.
Air force
An air force is the branch of a country's military which fights in the air. The air force is made up of aircraft such as fighters, bombers, helicopters and transport aircraft. When a navy has its own air force it is called Naval Aviation.
Air forces began in the early 20th century, usually as part of the army. Most countries separated their air forces in the 1930s and 1940s.
Aircraft in an air force sometimes fly in a formation. Formations are when the aircraft fly in a pattern. Air forces is part of the military.
The biggest air force in the world is the United States Air Force (USAF).
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