A square yard (sq yd or yd²) is a unit of area commonly used in the United States and a few other countries. It is defined as the area of a square with sides that each measure one yard (3 feet) in length.
In terms of square feet, one square yard is equal to 9 square feet (1 yard * 1 yard = 3 feet * 3 feet = 9 square feet).
In terms of square meters, one square yard is approximately equal to 0.836127 square meters.
Square yards are often used in various applications, including real estate, landscaping, and construction, especially in the United States where the customary system of measurements is still prevalent.
In physics, particularly in the field of nuclear and particle physics, a "barn" is a unit of area used to describe the likelihood of nuclear reactions or scattering events. The name "barn" comes from the idea that it's a very large target area, as if hitting the broad side of a barn were an easy task.
The barn is not part of the International System of Units (SI), but it's a widely recognized unit in nuclear physics. One barn is equal to 1 square femtometer (fm²), which is an incredibly small area. Specifically:
1 barn (b) = 1 square femtometer (fm²) = 10^(-28) square meters (m²)
To put it in perspective, a barn is used to describe the effective target area for nuclear reactions. Nuclear cross-sections, which describe the likelihood of nuclear interactions occurring, are often measured in barns. It's a unit that allows scientists to quantify the probability of certain atomic and subatomic processes taking place.