Rigging

Rigging (from Anglo-Saxon wrigan or wringing, "to clothe") is the apparatus through which the force of the wind is used to propel sailboats and sailing ships forward. This includes masts, yards, sails, and cordage.

Terms and classifications

Rigging is the mechanical sailing apparatus attached to the hull in order to move the boat as a whole. This includes cordage (ropes attached to the spars and sails in order to manipulate their position and shape), sails (aerofoils, usually made of fabric, used to catch the wind), and spars (masts and other solid objects sails are attached to). Cordage is more usually the term for stocks of rope, yarn, or other types of line in storage, before it has been put to some use in a vessel, whereafter is commonly referred to as part of the rigging.

Certain sail-plans are used for certain purposes according to their aerodynamic properties. All sailing vessels are classified according to their hull design and rigging.

In Antiquity, ships used only oars during battle. The sails could hinder the quick maneuvers needed in advancing the warship. Since the main rig took time to put up and take down, they implemented another rig, which was capable of being erected faster than the main rig. It was called the emergency rig, and was named as such because its main use was to get the ship to sail (away) faster if it got into trouble and the crew was not able to get the main rig up quickly enough. There is question on what equipment was in the emergency rig. Since there are no pictures/drawings of the emergency rig in use there are questions as to what exact material it consisted of. There is a comparison of the rig to a bow-sail, because it could be carried at all times. After the 4th century BC the existence of the emergency rig is questionable in the Athenian Navy, because there is evidence that the entire emergency rig was substituted for a lighter sail.

Khan Academy

Khan Academy is a non-profit educational organization created in 2006 by educator Salman Khan with the aim of providing a free, world-class education for anyone, anywhere. The organization produces short lectures in the form of YouTube videos. In addition to micro lectures, the organization's website features practice exercises and tools for educators. All resources are available for free to anyone around the world. The main language of the website is English, but the content is also available in other languages.

History

The founder of the organization, Salman Khan, was born in New Orleans, Louisiana, United States to immigrant parents from Bangladesh and India. After earning three degrees from the Massachusetts Institute of Technology (a BS in mathematics, a BS in electrical engineering and computer science, and an MEng in electrical engineering and computer science), he pursued an MBA from Harvard Business School.

In late 2004, Khan began tutoring his cousin Nadia who needed help with math using Yahoo!'s Doodle notepad.When other relatives and friends sought similar help, he decided that it would be more practical to distribute the tutorials on YouTube. The videos' popularity and the testimonials of appreciative students prompted Khan to quit his job in finance as a hedge fund analyst at Connective Capital Management in 2009, and focus on the tutorials (then released under the moniker "Khan Academy") full-time.

Tree

In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a woody trunk and branches as a way to tower above other plants to compete for sunlight. In looser senses, the taller palms, the tree ferns, bananas and bamboos are also trees. Trees tend to be long-lived, some reaching several thousand years old. The tallest known tree, a coast redwood named Hyperion, stands 115.6 m (379 ft) high. Trees have been in existence for 370 million years. It is estimated that there are just over 3 trillion mature trees in the world.

A tree typically has many secondary branches supported clear of the ground by the trunk. This trunk typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark which serves as a protective barrier. Below the ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil. Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into sugars by photosynthesis, providing the food for the tree's growth and development. Flowers and fruit may also be present, but some trees, such as conifers, instead have pollen cones and seed cones; others, such as tree ferns, produce spores instead.