AP Physics 1 Guided Notes 10 Fluids
47 FLUIDS, DENSITY, AND PRESSURE
1. Fluids: (A) Flows
(A) Defining Property
(B) Liquids and gases
(B) States of matter comprising fluids
(C) Describe properties on 1st (C) Takes shape of container filling from bottom, denser than gas, particles in constant
(D) Describe properties of 2nd random motion.
(D) Takes shape of container filling entire volume, less dense than liquid, particles in
constant random motion.
2. Volume (A) Amount of space measured in cubic meters, m3
(A) Define and give SI units
(B) L × 10−3 = m3 (or divide by 1000)
(B) Conversion: L to m3
(C) Conversion: mL to m3 (C) mL × 10−6 = m3 (or divide by 1,000,000)
(D) Conversion: cm3 to m3
(D) cm3 × 10−6 = m3 (or divide by 1,000,000)
3. Density (A) Amount of matter (mass) per (divide by) an amount of space (volume).
(A) Define
(B) Equation and units (B) , measured in kg/m3
(C) Uniform density
(D) Conversion: g/cm3 to kg/m3 (C) Density is the same everywhere in the system described. Take any two samples of
any size from anywhere in the system and they will have the same densities. The
(E) Density of pure (fresh) water
density of the samples will also equal the total density of the entire system.
(D) g/cm3 × 103 = kg/m3 (or multiply by 1000)
(E) 1000 kg/m3
4. Pressure (A) The total force of a fluid acting on an area of surface
(A) Define
(B) Equation and units (B) , measured in Pa (Pascal which is equivalent to a N/m2
(C) Conversion: atm to Pa
(C) atm × 105 = Pa (or multiply by 100,000)
5. Determine the density of a 250 g mass
occupying a volume of 0.50 L.
6. Determine the force on a round hatch,
radius 40 cm, of a submarine when the
surrounding water has a pressure of
5.0 atm.
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AP Physics 1 Guided Notes 10 Fluids
7. Gauge pressure (A)
(A) Define
(B) Equation (B)
8. Absolute pressure (A)
(A) Define
(B) Equation
(C) Atmospheric pressure at sea level (B)
(C)
9. A scuba diver is 15 m below the (A)
ocean’s surface.
(A) Determine the gauge pressure
acting on the diver.
(B) Determine the absolute pressure
acting on the diver.
(B)
10. (A)
A
D
B
C E F
(B)
(A) Rank pressure from high to low.
(B) Which variable in the pressure
equation is the most important? (C)
(C) How is pressure affected by
horizontal motion?
11.
h
1 2
A gas is trapped in the bulb on the left
by water (dark gray). The unknown
gas has enough pressure to cause the
water to form a column that is
h = 40 cm tall above point 2.
Determine the pressure of the the
trapped gas.
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AP Physics 1 Guided Notes 10 Fluids
12. A column of Mercury is trapped inside (A) (B)
a tube. The space above the fluid
column is a vacuum. The bottom of
the tube is immersed in a dish open to (C)
the air. The purpose is to find the
atmospheric pressure at point 1. The
fluid is mercury and the column is
78 cm tall.
1 2
13. A pump is used to move fluids from
one place to another, often to a higher
elevation. A pump in a fresh water
reservoir pumps water uphill into a
holding tank. The height between the
surface of the tank and the surface of
the water is 10 m. Determine the
pressure of the pump to keep water
flowing into the tank at constant
velocity.
tank
pump
48 BUOYANCY
14. Buoyancy (A)
(A) What creates force buoyancy?
(B) Equation
(C) Key to using the equation
(B)
(C)
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AP Physics 1 Guided Notes 10 Fluids
15. Fbouy pushes upward while Fg pulls (A)
downward. What will a mass do in
each situation below?
(B)
(A) Fbouy > Fg
(B) Fbouy < Fg
(C)
(C) Fbouy = Fg
16. A mass m is floating on (A) (B)
the surface of a liquid.
(A) Draw the FBD.
(B) Write the ΣF equation (C)
(C) Substitute known equations
17. A submerged mass m is (A) (B)
neutrally buoyant.
(A) Draw the FBD.
(B) Write the ΣF equation (C)
(C) Substitute known equations
18. A submerged mass m has (A) (B)
sunk to the bottom.
(A) Draw the FBD.
(B) Write the ΣF equation (C)
(C) Substitute known equations
19. A submerged mass m is (A) (B)
suspended by a string.
(A) Draw the FBD.
(B) Write the ΣF equation (C)
(C) Substitute known equations
20. An 80 kg mass floats in water with a
portion its mass sticking above the
surface. Determine the volume of fluid
displaced.
21. A 50 kg sphere, radius 20 cm is
completely submerged in water and
suspended by a spring. The spring is
stretched 30 cm from its rest length.
Determine the spring constant.
22. In air an object weighs 130 N. When it
is lowered completely into water it
appears to weight only 80 N.
Determine the buoyant force acting on
the object.
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AP Physics 1 Guided Notes 10 Fluids
49 ARCHEMIDES’ PRINCIPLE
23. Archemides’ principle
24. A 3 metric ton blimp must displace
___ metric tons of air.
25. A 100,000 ton ship must displace ___
tons of water.
26. Ice cubes float sticking out of the
water slightly. How does the level of
a glass change as ice melts? Explain.
27. If you are sitting raft floating in a
pool and you jump into the water,
how does the water level change?
Explain.
28. Archemides’ Principle is most useful (A) Neutrally Buoyant Floating
for objects that are not rising or
sinking. There are two possibile
scenarios shown at the right. For each
scenario do the following.
(A) Draw the force arrows on each
diagram.
(B) Write the balanced force (B)
equation.
(C) How does the mass of the object
compare to the mass of the fluid
displaced? (C) mobj mfd mobj mfd
(D) How does the volume of the
object compare to the volume of (D) Vobj Vfd Vobj Vfd
the fluid displaced?
(E) How does the height of the object
compare to the height of the fluid (E) hobj hfd hobj hfd
displaced?
(F) How does the density of the (F) ρobj ρfd ρobj ρfd
object compare to the density of
the fluid displaced?
29. In air an object weighs 130 N. When
it is lowered completely into water
(submerged) it appears to weight only
80 N. Determine the density of the
object.
30. A beaker is filled to the brim with (A)
water. A 600 g mass is lowered into
the beaker and completely submerges.
240 mL of water spills out of the
beaker.
(A) Determine the buoyant force (B)
acting on the mass.
(B) Determine the density of the
mass.
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AP Physics 1 Guided Notes 10 Fluids
31. A rectangular raft ( = 4 m, w = 3 m,
and h = 2 m) floats with only 25% of
its height sticking above the surface
of a lake. Determine the force of
buoyancy acting on the raft.
32. When an object is floating with a (A)
portion sticking above the surface is
there an easy way to determine
(A) the density if you are given the
portion sticking above the
surface? (B)
(B) the portion sticking above the
surface if you are given the
density?
50 FLOW RATE AND BERNOULLI’S LAW
33. Flow Rate Equation (A) (B)
(A) Version given
(B) Alternate version worth knowing
34. Water flows at 4.0 m/s through a pipe
with a diameter of 1.0 m. The pipe
narrows to a diameter of 0.5 m.
Determine the speed of the water in
the narrow section of pipe.
35. Determine the volume flow rate if
200 L of water pass a point in a pipe
every second.
36. What happens to the speed of a fluid
as a pipe narrows?
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AP Physics 1 Guided Notes 10 Fluids
37. Bernoulli’s Law (A)
(A) Equation version of Bernoulli’s
Law given
(B)
(B) Format of Bernoulli’s Law that
will be tested
(C) Label the diagram with the letters (C)
corresponding to the equation.
38. What does Bernoulli’s Law imply
regarding the relationship between a
fluids velocity & its internal pressure?
39. Key substitutions (A)
(A) If the arbitrary line is drawn
through the point
(B)
(B) If a tube is open to the
atmosphere
(C) If there is a vertical tube above or (C)
below
(D) If one section of pipe has a very
large area compared to another (D)
section of pipe (leaking
container).
40. Apply Bernoulli’s Equation to the (A)
scenario at the right.
(A) Draw the arbitrary horizontal line
and label the y’s, A’s, and v’s.
(B) Write the general version of
Bernoull’s equation useful when
a tube changes.
(C) Simplify it as much as possible. (B)
(D) What other equation can also be
solved? (C)
(D)
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AP Physics 1 Guided Notes 10 Fluids
41. Use Bernoulli’s equation and simplify it as much as possible.
1 2
42. Ventury Tube: Use Bernouli’s Law to find the
relationship between Δh and velocity.
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AP Physics 1 Guided Notes 10 Fluids
43. Leaking containers
(A) Solve for the velocity of the water leaving the opening at point 2.
(B) Solve for the horizontal displacement of the water as it falls
44. In a siphone the leak is essentially moved outside the container. In the diagram below the fluid is water. The height between
the surface of the water and the end of the hose is h = 30 cm and the hose has a radius of 0.5 cm. Initially your thumb is
covering the opening of the hose.
(A) Determine the force on your thumb.
(B) You remove your thumb and water begins to flow out the end of the hose.
(C) Determine the horizontal distance that the water is move before striking the floor.
