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Fluids

Fluids. AP Physics B. Fluids. A fluid is anything that can flow Liquids Gases. Density review. r = m / V r : density (kg/m 3 ) m: mass (kg) V: volume (m 3 ) r is the Greek letter “rho”; it is NOT a P! Capital P is pressure. Lowercase p is momentum (you’ll learn later).

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Fluids

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  1. Fluids AP Physics B

  2. Fluids • A fluid is anything that can flow • Liquids • Gases

  3. Density review • r = m / V • r : density (kg/m3) • m: mass (kg) • V: volume (m3) • r is the Greek letter “rho”; it is NOT a P! Capital P is pressure. Lowercase p is momentum (you’ll learn later). • You should remember how to do density calculations from Chemistry; review if you don’t! We don’t have time.

  4. Pressure • P = F / A • P : pressure (Pa) • F : force (N-Newton) • A : area (m2) • Pressure unit: pascal (1 Pa = 1 N/m2) • A lot of times, the force a fluid exerts is the weight of the fluid…

  5. What is weight? • Weight is the pull of gravity on a mass • Weight is a force • We can sometimes replace the F with mg • g = 9.8 m/s2 (this is a constant)

  6. Observations of Fluids • Exerts pressures in all directions • Pressure is always to surfaces • If it were parallel, it would flow • The force on a surface caused by pressure is always perpendicular to every surface at every location

  7. Atmospheric pressure • Usually at about 101000 Pa • Differences in Patm cause winds Low Patm inside eye of a hurricane contributes to the severe winds & the development of the storm surge.

  8. Pressure of a Liquid • P = rgh (How do you get this formula?) • P : pressure (Pa) • r : density (kg/m3) • g : acceleration constant (9.8 m/s2) • h : height of liquid column (m) • This is often called hydrostatic pressureif the liquid is water. It does NOT include atmospheric pressure! • It is also sometimes called gauge pressure, since a diver’s pressure gauge obviously never includes Patm! • How would we get absolute pressure?

  9. AP Objective!!! • No matter the shape of the container…. Pressure at equal depths within a uniform liquid is the same

  10. Just to be sure you got it… Gauge pressure measures the pressure of the fluid….. is measured in exclusion ofPatm. It does NOT include Patm.

  11. Pascal’s Principle • Pressure exerted on a fluid is transmitted evenly throughout the fluid • Hydraulic lifts • Pressurein = Pressureout

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