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PRENTICE HALL SCIENCE EXPLORER
PHYSICAL SCIENCE
CHAPTER 11
FORCES IN FLUIDS
11-1 Pressure
Objectives:
• Tell what pressure depends on.
• Explain how fluids exert pressure.
• Relate how fluid pressure changes with elevation and depth
A. What Is Pressure?
1. Pressure and Area
a.) Pressure is defined as ___________________________________.
b.) As area is __________________ the pressure ______________________.
2. Calculating Pressure
a.) Pressure is calculated by dividing the total ___________ by the ________.
𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹
b.) 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 = 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴
B. Fluid Pressure – A fluid is a material that can easily __________________.
1. What Causes Fluid Pressure?
a.) As particles in a fluid __________________ with their container and with
objects in the fluid, they produce __________________.
b.) All of the forces exerted by the individual particles in a fluid combine to
make up the __________________ exerted by the fluid.
2. Air Pressure
a.) __________________ is a fluid.
b.) We live at the bottom of about ____________________________ of air.
c.) Each cubic meter of air has a mass of about __________________.
d.) The force with which air presses down on Earth and those objects on Earth
is known as _____________________________.
3. Balanced Pressure
a.) At sea level, air pressure is about __________________.
b.) Fluid pressure is exerted equally in _________________________.
c.) Also, pressure from fluids __________________ your body balance
pressure from fluids __________________ your body.
d.) If the air were removed from a can, the outside air pressure would
____________________ it.
C. Variations In Pressure
1. Atmospheric Pressure and Elevation – as you travel __________________ in
altitude, air pressure __________________ explaining why your ears “pop”.
2. Water Pressure and Depth
a.) Water pressure __________________ as depth __________________s.
b.) At 10 meters, the water pressure is __________________ atmospheric
pressure.
c.) The pressure at the bottom of the ocean (or any body of water) is the
combined total of the __________________ and __________________
above that point.
d.) In the deepest parts of the ocean, water pressure can reach
__________________ that of air pressure.
3. Measuring Pressure
a.) Atmospheric pressure can be measured with an instrument called a
__________________.
b.) Rapidly decreasing air pressure usually means __________________ is on
the way.
c.) Air pressure is expressed in several ways:
i.) Normal air pressure is ____________________________________.
ii.) Normal air pressure is ____________________________________.
iii.) Normal air pressure is ____________________________________.
11-2 Floating And Sinking
Objectives:
• Explain what the effect of the buoyant force is.
• Demonstrate how you can use density to determine whether an object will float or
sink in a fluid.
A. Buoyancy
1. Gravity and the Buoyant Force
a.) __________________ is the ability to float.
b.) Water and all other fluids exert an __________________ force on all
objects submerged in them called the _____________________________.
c.) The buoyant force acts in the __________________ direction as the force
of gravity, so it makes an object feel lighter.
d.) An object sinks if the force of __________________ (its weight) is greater
than the __________________ force.
2. Archimedes’ Principle
a.) Archimedes’ Principle states that the buoyant force acting on a submerged
object is equal to the weight ______________________ the object
displaces.
b.) If the object weighs less than the weight of the fluid it displaces,
__________________.
c.) If the object weighs more than the weight of the fluid it displaces,
__________________.
B. Density
1. What Is Density?
a.) The density of a substance is its __________________ per unit volume.
𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀
b.) 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷 = 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉
2. Comparing Densities of Substances
a.) All __________________ have their own density.
b.) The density of water is __________________.
c.) Materials with lesser densities ___________________________ of
material with greater densities.
3. Changing Density
a.) Ice float because it has __________________ than water.
b.) Submarines can __________________ their density in order to float or
sink.
11-3 Pascal’s Principle
Objectives:
• State Pascal’s principle
• Explain how a hydraulic system works.
A. Transmitting Pressure In A Fluid
1. What Is Pascal’s Principle?
a.) In the 1600’s French mathematician Blaise Pascal developed a principle
that explains how pressure is _________________________ in a fluid.
b.) Pascal’s __________________ is used for the SI unit of pressure.
c.) Pascal’s principle states: When __________________ is applied to a
__________________ fluid, the change in pressure is transmitted
equally to all parts of the fluid.
2. Using Pascal’s Principle – The ____________________________________
explained in Figure 15 on page 390 makes use of Pascal’s principle.
B. Hydraulic Systems
1. A hydraulic system uses __________________ to transmit pressure in a
confined fluid.
2. The hydraulic system multiplies __________________ by using the same
pressure on a ___________________________.
a.) ____________________________________
b.) ____________________________________
11-4 Bernoulli’s Principle
Objectives:
• Explain how, according to Bernoulli’s principle, fluid pressure is related to the
motion of the fluid.
• List some of the applications of Bernoulli’s principle.
A. Pressure And Moving Fluids
1. Fluid Motion
a.) Fluids move from an area of ___________ to an area of ___________
pressure.
b.) Removing ___________ from a straw causes the pressure exerted on the
fluid in a drink to ____________________________________ the straw.
2. What Is Bernoulli’s Principle?
a.) In the 1700’s Swiss scientist Daniel Bernoulli discovered that the pressure
in a moving fluid was __________________ than that of a fluid sitting
still.
b.) Bernoulli’s principle states: As the speed of a moving fluid
_______________, the pressure within the fluid __________________.
B. Applying Bernoulli’s Principle
1. Objects in Flight
a.) Airplane wings are designed with a _________________________ on top
that is __________________ than the surface on bottom.
b.) As the wing slices through the air, the air moving across the top of the
wing must travel __________________ than the air moving across the
bottom of the wing.
c.) The decrease in pressure creates “__________________” on the wing.
2. Atomizers
a.) In an __________________, air is squeezed past a tube that opens into a
container of liquid.
b.) The decrease in air pressure caused by the moving air causes the fluid to
__________________ in the tube and be blown out.
3. Chimneys
a.) As air moves outside the chimney, its pressure is __________________
than the still air __________________ the chimney.
b.) The difference in pressure causes the __________________ in the
chimney.
4. Flying Disks
a.) A Frisbee uses the same principle as the __________________ to
maintain flight.