Thursday 6/18
PHYS 2010
Nathalie Hoffmann
University of Utah
Gauge Pressure
• 𝑝 − 𝑝0 = 𝑔𝑎𝑢𝑔𝑒 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒
• 𝑝0 is the absolute pressure
• Gauge pressure shows how much the pressure exceeds atmospheric
pressure/absolute pressure
Archimedes’ Principle
• The buoyant force on an object immersed in a fluid is equal to the
weight of the fluid that the object displaces.
Volume Flow Rate (Q)
• Equation of Continuity:
• 𝑄1 = 𝑄2 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
•𝑄=
ΔV
Δt
• (flow rate gives the volume of fluid passing a certain point in a given time
interval)
• 𝑄 = 𝐴𝑣
Steady vs. Unsteady Flow
• Steady flow: the flow pattern at any given point does not change with
time, at any given point the flow velocity remains constant with time;
does not mean the flow velocity is constant everywhere
• Unsteady flow: the flow velocity at a given point can change with
time
Laminar vs. Turbulent Flow
• Laminar flow: each bit of fluid follows a path called a streamline,
which do not cross
• Turbulent flow: no streamlines, adjacent bits of fluid can follow very
different paths
Viscosity
• Viscosity is an intrinsic resistance to flow. Because adjacent parts of a
fluid move at different velocities, the parts rub and exert frictional
forces on each other.
Bernoulli’s Principle
• In a moving fluid, the pressure is low where the fluid is moving rapidly
• 𝑝1 +
1
𝜌𝑣12
2
+ 𝜌𝑔𝑦1 = 𝑝2 +
1
𝜌𝑣22
2
+ 𝜌𝑔𝑦2
• Assumptions: steady, laminar flow
Bernoulli’s Principle
• In a moving fluid, the pressure is low where the fluid is moving rapidly
• 𝑝1 +
1
𝜌𝑣12
2
+ 𝜌𝑔𝑦1 = 𝑝2 +
1
𝜌𝑣22
2
+ 𝜌𝑔𝑦2
• Assumptions: steady, laminar flow