13.1  Fluid Pressure (continued)

Pressure

The comfort of the plush theater seats shown in Figure 1 is related to pressure—the result of a force distributed over an area. A theater seat's large padded seat and back offer a larger area to support your weight than a bicycle seat does. Thus, the theater seat exerts less pressure on you and is more comfortable than the bicycle seat.

Many other everyday situations also involve pressure. A sharp pencil easily pokes a hole through a sheet of paper, whereas the eraser end of the pencil does not. Why is this? The reason is the same—pressure. The pencil point has a much smaller area than the eraser, so it exerts much greater pressure than the eraser. The greater pressure exerted by the pencil point allows it to pierce the paper easily.

  To calculate pressure, divide the force by the area over which the force acts.


In the formula, force should be in newtons (N) and area should be in square meters (m²). The resulting unit, newtons per square meter (N/m²), is the SI unit of pressure, also known as a pascal (Pa). The pascal is named for French scientist Blaise Pascal (1623–1662). Pressures are often stated in units of kilopascals (kPa). Note that 1 kPa is 1000 Pa.

Consider a box with a weight of 2700 newtons resting on the ground. If the area of the box touching the ground is 1.5 square meters, what pressure does the box exert on the ground?