What does it mean if pressure is described as being less than that exerted by the atmosphere?

When pressure is described as being less than that exerted by the atmosphere, it is referred to as negative pressure. This occurs when the pressure inside a system is lower than the surrounding atmospheric pressure. In practical terms, negative pressure can be found in various applications, such as vacuum systems or suction devices, where it is necessary to create a lower pressure to draw in fluids or gases.

Understanding the concept of negative pressure is crucial for ensuring proper functioning of plumbing systems, as it can affect the flow of water and other fluids, leading to issues like backflow if not managed correctly. It is vital in applications where containment and control of certain substances are required to prevent contamination or unwanted leakage.

In contrast, positive pressure refers to pressure that is higher than atmospheric pressure, equal pressure indicates a balance with atmospheric pressure, and static pressure refers to the pressure exerted by a fluid at rest, which may not necessarily be lower than atmospheric pressure. Each of these terms describes different states of pressure and highlights the importance of understanding how pressure works in plumbing systems.