CHAPTER
9
Chapter Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
The particles in a gas are spread out more than the particles in a liquid, so there are more empty spaces
between the gas particles. When a gas is compressed, its particles are squeezed together. There is less
empty space between the particles in a liquid, so a liquid is less compressible than a gas.
2.
Sample answer: Two hydraulic systems are the human circulatory system and the hydraulic ram in a
backhoe. Two pneumatic systems are the system that powers a pneumatic hammer and the system that
opens and closes bus doors.
3. (a)
(b)
A typical fluid system consists of pumps that force fluids through conductors, such as hoses or pipes;
valves that control the movement of fluids; and a pressure gauge to monitor how much pressure is
being generated.
Sample answer:
pressure gauge
valve
pump
conductor
4.
Change to a fluid
Results in
increase in pressure
volume: decrease
temperature: increase
increase in temperature
volume: increase
pressure: increase
increase in volume of the container
pressure: decrease
temperature: decrease
5. (a)
(b)
6.
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Sample answer: Pressure is the force pressing against the surface of something. Pressure can be
applied in any direction, from the outside or from within.
Pressure is measured in pascals, which are equivalent to the force in newtons per square metre of
surface area.
Air pressure pushes against your body in all directions.
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7.
Pascal’s Law states that a force applied to a contained fluid is transferred throughout the fluid equally in
all directions. For example, in the sketch below, when the hands press down on the balloon, the force is
distributed through the air to every part of the balloon.
8.
Sample answer: Pascal’s Law is used today in devices, such as hydraulic brakes. Brakes need to apply a
controlled force equally across a moving part; fluids transfer forces in such a way as to achieve this.
9.
Valves control the direction of blood flow in the human circulatory system. Valves open and close to keep
blood flowing in the correct direction throughout the body.
10.
Both hydraulic and pneumatic systems use pressurized fluids to do work. Both systems contain the same
basic components, such as pumps and conductors. However, hydraulic systems use pressurized liquids
and pneumatic systems use gases.
11.
Both atmospheric pressure and water pressure act in all directions and are caused by the force of moving
particles pressing against a body. However, water particles are heavier than air particles and are packed
more tightly together. Therefore, water pressure is greater than atmospheric pressure, if the depth of both
fluids is the same.
12.
Sample answer: Valves are “gates” that are placed in both hydraulic and pneumatic systems to control the
flow of fluids. When a valve opens, fluids flow into the next part of the system. The valve then closes to
keep the fluids from flowing backwards in the wrong direction.
13.
Sample answer: I play the trumpet, which has three valves that you press with your fingers to control the
flow of air through the instrument to play different notes. I have also heard people refer to water valves
and shower valves, which open when you turn on the faucet to let water flow out the spigot.
WHAT DO YOU UNDERSTAND?
14.
Sample answer: Three benefits of fluid-powered systems are that they allow a few people to do the work
of many, they transfer forces equally in all directions, and they can recycle fluids in a closed system. Three
costs of fluid-powered systems are that they can leak and damage the environment, they can eliminate
jobs, and they can be expensive to build and maintain.
15.
The system should be hydraulic. Liquids are much less compressible than gases. Therefore, when you
apply a force to one part of a hydraulic system, it will be applied more quickly throughout the rest of the
system because none of the force is used to compress the gas.
16.
Pressure is spread over the entire surface area of a body. Therefore, when a person lies on a bed of nails,
only a small percentage of his or her weight is pressing down against each individual nail. The force is
not great enough to puncture the skin.
17. (a)
(b)
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You should apply the effort to Piston B, the smaller piston. According to Pascal’s Law, force is
transferred equally through a fluid in every direction. Therefore, a larger piston, such as Piston A,
will have more forces pressing against it and will move with greater force.
If you apply the force to Piston A, the fluid will be moving from a larger cylinder into a smaller
cylinder. This will cause the smaller piston, Piston B, to move farther than Piston A would move if
the direction of the force were reversed.
Unit C: Fluids
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18.
Your ears “pop” in an airplane because the air pressure changes rapidly. As the airplane descends and the
air pressure increases, the air particles outside your body press with greater force against your eardrum.
Your body equalizes this pressure by forcing air from your lungs through channels that lead to your ears.
You hear the movement of air particles against your eardrums as a “popping” sound.
19.
Roller coasters are starting to use hydraulics in their launching systems. In a typical hydraulic launch
system, hydraulic pumps move pistons with tremendous force. The force causes a tightly wound cable
attached to the coaster train to unwind. The unwinding cable helps shoot the train out of the gate at high
speed, unlike traditional roller coasters, which depend mainly on gravity to get the coaster train moving.
20.
If a snorkel is too long, the swimmer will not be able to exhale with enough force to expel the old,
oxygen-depleted air from the snorkel. Instead, it remains trapped inside the snorkel and prevents fresh
oxygen from reaching the swimmer when he inhales.
21.
When a tennis ball is hit, the side that touches the racquet is forced inward. This compresses the ball
(decreases its volume). When the volume of a gas decreases, its pressure increases. Therefore, the pressure
inside the tennis ball probably increases when it is hit.
22.
A scuba diver’s air tank is filled with highly compressed air. The air particles are squeezed tightly together,
which allows a lot more air to fit inside the tank than if the air had not been compressed. The gas is
allowed to decompress before the diver breathes it.
23.
Sample answer: I have seen hydraulic systems used on water slides and hydraulic rescue tools on TV.
I have seen pneumatic hammers at construction sites and blood pressure gauges at the doctor’s office.
SOLVE A PROBLEM!
24. (a)
Sample answer: Put exactly 5 mL of water into a 10 mL graduated cylinder. Put exactly 5 mL of
alcohol into a second 10 mL graduated cylinder. Cover the tops of the cylinders with plastic wrap to
prevent evaporation. Place the two cylinders in a warm-water bath (30 to 40 °C—check temperature
with a thermometer) for 5 to 10 minutes, so that the liquids inside the cylinders reach the same
temperature as the water. Remove the cylinders from the bath, place them on a flat surface and record
the volume of the liquid in each cylinder. Repeat using an ice-water bath.
(b)
Sample answer: I am changing the kind of liquid in the graduated cylinder. I am also changing the
temperature of the liquid between tests. I am keeping constant the amount of liquid, the cylinder
size, the temperatures of the baths, and the length of time the cylinders are in the baths.
(c)
Sample answer: I will wear safety goggles and an apron. I will clean up all spills immediately. I will
not eat or drink anything while I am doing the experiment. I will keep open flames and sparks away
from the rubbing alcohol.
CREATE AND EVALUATE!
25.
Sample answer:
handle
fluid flow
butterfly
When the butterfly is perpendicular
to the walls of the tube, the valve
is closed and no fluid can flow.
When the butterfly is parallel to
the walls of the tube, the valve
is open and fluid can flow.
Students should ask one another questions about when this type of valve would be useful, when it would
not be useful, how it controls the flow of fluid, and what parts it uses.
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26.
Sample answer: The benefits of pipelines include the efficient transportation of fluids over great
distances. The costs include damage to the environment should the pipelines leak; the land may also need
to be cleared or reshaped in order to build the pipelines, which could disturb animals and people living
nearby. With strict standards of quality and careful supervision during construction and maintenance
after construction, pipelines need not cause lasting damage to the environment. The certain benefits of
efficiently transporting such crucial fluids as water and oil outweigh the possible costs.
27.
Students’ concept maps should clearly indicate their understanding of the relationships between the
concepts and vocabulary presented in this chapter. When students study others’ concept maps, they
should try to provide constructive criticisms to other students. Students should consider whether others
comments on their own concept maps are valid, and make changes as necessary.
REFLECT ON YOUR LEARNING
28. (a)
Sample answer: The idea that most relates to my life is the idea that so many technologies take
advantage of pressurized fluids in hydraulic and pneumatic systems.
(b)
Sample answer: Every time a bus door opens and I get on or off the bus, I am experiencing a
pneumatic system. Similarly, when the dentist presses the foot pedal and the dentist’s chair leans back
or becomes higher, I am experiencing fluid-powered technology. As well, the brakes in my parents’
car are powered by hydraulics.
29. (a)
Sample answer: Pressurized fluids affect our lives every day because they are used in so many different
kinds of technology. For example, turning on the water faucet in my bathroom opens a valve that
allows pressurized water to flow up the pipes and into the sink or shower. Similarly, using a can of
compressed air to clean the dust off my keyboard activates a simple, but powerful pneumatic system.
Fluids under pressure are everywhere in nature too. For example, changing air pressure in the
atmosphere can affect whether it rains, snows, or remains sunny. And blood pumps through my
body—and the bodies of other animals—thanks to a hydraulic circulatory system.
(b)
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Sample answer: How exactly do the hydraulic systems in a car or other vehicle work? Are there
pressurized fluid systems in organisms other than humans?
Unit C: Fluids
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