Troy-Bilt Pony 42 in. 15.5 HP Briggs and Stratton 7-Speed Manual Drive Gas Riding Lawn Tractor

Fifteen or 15 may refer to:

• 15 (number), the natural number following 14 and preceding 16
• one of the years 15 BC, AD 15, 1915, 2015

5 (five) is a number, numeral and digit. It is the natural number, and cardinal number, following 4 and preceding 6, and is a prime number.

Humans, and many other animals, have 5 digits on their limbs.

7 (seven) is the natural number following 6 and preceding 8. It is the only prime number preceding a cube.

As an early prime number in the series of positive integers, the number seven has greatly symbolic associations in religion, mythology, superstition and philosophy. The seven classical planets resulted in seven being the number of days in a week. 7 is often considered lucky in Western culture and is often seen as highly symbolic. Unlike Western culture, in Vietnamese culture, the number seven is sometimes considered unlucky.

Gas is one of the four fundamental states of matter. The others are solid, liquid, and plasma. A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes gases from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer.

The gaseous state of matter occurs between the liquid and plasma states, the latter of which provides the upper-temperature boundary for gases. Bounding the lower end of the temperature scale lie degenerative quantum gases which are gaining increasing attention. High-density atomic gases super-cooled to very low temperatures are classified by their statistical behavior as either Bose gases or Fermi gases. For a comprehensive listing of these exotic states of matter, see list of states of matter.

A lawn () is an area of soil-covered land planted with grasses and other durable plants such as clover which are maintained at a short height with a lawn mower (or sometimes grazing animals) and used for aesthetic and recreational purposes—it is also commonly referred to as part of a garden. Lawns are usually composed only of grass species, subject to weed and pest control, maintained in a green color (e.g., by watering), and are regularly mowed to ensure an acceptable length. Lawns are used around houses, apartments, commercial buildings and offices. Many city parks also have large lawn areas. In recreational contexts, the specialised names turf, parade, pitch, field or green may be used, depending on the sport and the continent.

The term "lawn", referring to a managed grass space, dates to at least the 16th century. With suburban expansion, the lawn has become culturally ingrained in some areas of the world as part of the desired household aesthetic. However, awareness of the negative environmental impact of this ideal is growing. In some jurisdictions where there are water shortages, local government authorities are encouraging alternatives to lawns to reduce water use. Researchers in the United States have noted that suburban lawns are "biological deserts" that are contributing to a "continental-scale ecological homogenization." Lawn maintenance practices also cause biodiversity loss in surrounding areas.

A pony is a type of small horse (Equus ferus caballus). Depending on the context, a pony may be a horse that is under a given height at the withers, or a small horse with a specific conformation and temperament. Compared to a larger horse, a pony may have a thicker coat, mane and tail, with proportionally shorter legs, a wider barrel, heavier bone, a thicker neck and a shorter, broader head. The word pony derives from the old French poulenet, meaning foal, a young, immature horse.^: 1041

In modern use, some organizations may define a pony as a mature horse below a certain height at the withers; this may vary from about 142 cm (14.0 h) to nearly 150 cm (14.3 h). (Note: 14.3 hands means 14 hands and 3 inches, i.e. decimally 14.75 hands.) Some people classify an animal as either horse or pony from its pedigree and phenotype, no matter what its height. A full-sized horse may sometimes even be called a pony as a term of endearment.

In kinematics, the speed (commonly referred to as v) of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a non-negative scalar quantity. The average speed of an object in an interval of time is the distance travelled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero. Speed is the magnitude of velocity (a vector), which indicates additionally the direction of motion.

Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph). For air and marine travel, the knot is commonly used.

The fastest possible speed at which energy or information can travel, according to special relativity, is the speed of light in vacuum c = 299792458 metres per second (approximately 1079000000 km/h or 671000000 mph). Matter cannot quite reach the speed of light, as this would require an infinite amount of energy. In relativity physics, the concept of rapidity replaces the classical idea of speed.

A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery such as that used in agriculture, mining or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially (and originally) tillage, and now many more. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.

Troy (Ancient Greek: Τροία, romanized: Troíā; Latin: Trōia; Hittite: 𒆳𒌷𒋫𒊒𒄿𒊭, romanized: Truwiša/Taruiša) or Ilion (Ancient Greek: Ίλιον, romanized: Ī́lion, Hittite: 𒌷𒃾𒇻𒊭, romanized: Wiluša) was an ancient city located in present-day Hisarlık, Turkey. The place was first settled around 3600 BC and grew into a small fortified city around 3000 BC. During its four thousand years of existence, Troy was repeatedly destroyed and rebuilt. As a result, the archeological site that has been left is divided into nine layers, each corresponding to a city built on the ruins of the previous. Archaeologists refer to these layers using Roman numerals. Among the early layers, Troy II is notable for its wealth and imposing architecture. During the Late Bronze Age, Troy was called Wilusa and was a vassal of the Hittite Empire. The final layers (Troy VIII-IX) were Greek and Roman cities which in their days served as tourist attractions and religious centers because of their link to mythic tradition.

The archaeological site is open to the public as a tourist destination, and was added to the UNESCO World Heritage list in 1998. The site was excavated by Heinrich Schliemann and Frank Calvert starting in 1871. Under the ruins of the classical city, they found the remains of numerous earlier settlements. Several of these layers resemble literary depictions of Troy, leading some scholars to conclude that there is a kernel of truth underlying the legends. Subsequent excavations by others have added to the modern understanding of the site, though the exact relationship between myth and reality remains unclear and there is no definitive evidence for a Greek attack on the city.^{(ppxiv, 180–182)}