What is the SI unit for pressure, equivalent to one newton per square meter?

The SI unit for pressure is the pascal (Pa), which is defined as one newton of force applied over an area of one square meter. This relationship stems from the fundamental definition of pressure, which is force per unit area. Thus, when you divide a newton (the SI unit of force) by a square meter (the SI unit of area), you arrive at the pascal.

Using this definition clarifies why the pascal is the correct answer. The other units mentioned—bar, atmosphere, and newton—represent different measures or concepts. For instance, a bar is a unit of pressure that is not part of the SI system and is approximately equal to 100,000 pascals, while the atmosphere is another unit of pressure that is defined as being equal to 101,325 pascals. The newton, on the other hand, measures force rather than pressure, which further distances it from being the correct answer. Therefore, pascal is the standard and accepted SI unit for measuring pressure.