Pressure

Definition

Pressure is defined as the force exerted per unit area on a surface, typically measured in Pascals (Pa). It plays a crucial role in fluid dynamics, affecting how fluids behave under various conditions, including their density, viscosity, buoyancy, and flow behavior through expansion waves. Understanding pressure is vital for analyzing how fluids interact with their environment and with each other.

5 Must Know Facts For Your Next Test

1. Pressure can change with depth in a fluid due to the weight of the fluid above, following the principle that pressure increases with depth in incompressible fluids.
2. Viscosity affects how pressure is distributed within a fluid; higher viscosity can lead to greater pressure drops in flow systems due to internal friction.
3. Buoyant forces acting on an object submerged in a fluid are determined by the difference in pressure between the top and bottom surfaces of the object.
4. In supersonic flows, Prandtl-Meyer expansion waves result from changes in pressure and density as a fluid accelerates, which can cause significant changes in flow characteristics.
5. Pressure differences are essential for understanding flow behavior; fluids naturally move from regions of high pressure to low pressure.

Review Questions

• How does hydrostatic pressure influence buoyancy in fluids?
  • Hydrostatic pressure plays a critical role in buoyancy by creating differences in pressure that act on submerged objects. As the depth increases, hydrostatic pressure increases, resulting in a greater upward force on the bottom surface of an object than on its top surface. This difference causes an upward buoyant force, which can determine whether an object floats or sinks.
• In what ways does viscosity affect the relationship between pressure and flow rate in a fluid?
  • Viscosity influences how easily a fluid flows under an applied pressure. In highly viscous fluids, greater pressure is needed to achieve the same flow rate compared to less viscous fluids. This relationship is described by the Hagen-Poiseuille equation for laminar flow, which shows that flow rate is directly proportional to pressure difference and inversely proportional to viscosity.
• Evaluate how changes in pressure impact fluid behavior during Prandtl-Meyer expansion waves and their relevance to supersonic flows.
  • During Prandtl-Meyer expansion waves, pressure decreases as the fluid expands rapidly when transitioning from subsonic to supersonic speeds. This reduction in pressure leads to changes in density and velocity, allowing for smooth expansion without shock waves. Understanding these changes is crucial for designing high-speed vehicles and ensuring stability and control in supersonic flight conditions.

Related terms

Hydrostatic Pressure:

The pressure exerted by a fluid at rest due to the force of gravity, which increases with depth in the fluid.

Dynamic Pressure:

The pressure associated with the motion of a fluid, calculated as one-half the fluid's density multiplied by the square of its velocity.

Absolute Pressure: The total pressure measured relative to a perfect vacuum, encompassing both atmospheric pressure and any additional pressure exerted by a fluid.