A square rod (US survey) is a unit of area measurement used in the United States for land surveying and legal property descriptions. It is different from the standard square rod or square pole and is based on the U.S. survey foot, which is a historical unit of length used in land surveying in the United States. The U.S. survey foot is slightly different from the international foot.
One square rod (US survey) is equal to 1/160th of an acre. In terms of area, this is approximately equal to 25.29285264 square meters (m²) or 0.00625 acres.
This unit is used in land-related applications, especially in the United States, where the U.S. survey square rod is employed for legal and historical reasons in land surveys, property descriptions, and land records. It's important to be aware of the specific units being used when dealing with land measurements in the United States to avoid discrepancies or errors.
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.