Long Tons (long-ton) to Slugs (slug) conversion

What is the Long Ton?

The long ton is a unit of mass in the British imperial system, historically used for weighing bulk commodities such as coal, ore, and shipping cargo. It is equal to 2,240 pounds and remains familiar in the United Kingdom and in maritime contexts.

Definition

The long ton is defined as exactly 2,240 pounds avoirdupois. Since one pound equals 0.45359237 kg exactly, its SI value is:

$$1\ \text{long-ton} = 1016.05\ \text{kg}$$

Equivalently, the long ton equals 20 hundredweight (cwt) of 112 lb each, distinguishing it from the 2,000 lb US short ton and the 1,000 kg metric tonne.

Origin and History

The long ton descends from the medieval English "tun," a large cask used to ship wine, whose full weight was standardized in trade. The avoirdupois system fixed the hundredweight at 112 pounds (eight stone of 14 lb), and twenty of these made the ton, giving 2,240 lb. This "long" hundredweight and ton became the standard for British commerce and were carried throughout the Commonwealth and colonial trade.

Law and Notable Facts

The long ton is the British/imperial ton, contrasted with the 2,000 lb US short ton and the 1,000 kg metric tonne (megagram). It is legally recognized in the United Kingdom, though the metric tonne has largely replaced it for official trade. Notably, the long ton (1016 kg) sits remarkably close to the metric tonne (1000 kg), differing by only about 1.6%, which is why "ton" and "tonne" are often used loosely as near-equivalents in shipping.

Real-World Examples and Conversions

• A long ton equals 1016.05 kg, about 16 kg heavier than a metric tonne.
• Ship displacement and cargo were traditionally quoted in long tons; a 10,000 long ton vessel carries roughly 10,160 metric tonnes.
• One long ton (2,240 lb) is 240 lb heavier than one US short ton (2,000 lb), a 12% difference.
• A long ton of coal (1016 kg) is a typical unit still cited in older British mining and heating records.

What is the Slug?

The slug is the unit of mass in the British Gravitational (foot–pound–second) system of units, used chiefly in engineering and physics involving imperial units.

Definition

The slug is the mass that accelerates at 1 foot per second squared when a force of one pound-force is applied:

$$1\ \text{slug} = 14.5939\ \text{kg}$$

It follows from $1\ \text{slug} = 1\ \text{lbf} \cdot \text{s}^2/\text{ft}$, giving exactly 14.593902937206 kg. A one-slug mass therefore weighs about 32.174 pounds-force under standard gravity.

Origin and History

The slug was introduced in the early 20th century to give the imperial system a coherent mass unit consistent with Newton's second law, avoiding confusion between the pound as a unit of mass and the pound-force as a unit of force. The name was popularized by British physicist Arthur Mason Worthington.

Law and Notable Facts

The slug is not part of SI but remains in use in some U.S. and British engineering fields, especially aeronautics and ballistics. Its counterpart is the "slinch" (pound·s²/inch), which is exactly 12 times larger.

Real-World Examples and Conversions

An object weighing 32.174 lbf at standard gravity has a mass of exactly 1 slug (≈14.59 kg). A 160-pound person has a mass of roughly 4.97 slugs. One slug is close to the mass of a typical bowling-ball-and-a-half, about 14.6 kg.