CHAPTER 5 ANSWERS missing cyu 5.8 # 1 & 2
CYU 5.2 p. 144
1. (a) When designing a barge, engineers must consider the weight (force of gravity) of the barge, the capacity
of the barge, and the buoyant force acting on it.
(b) To ensure that a barge is stable, engineers must determine that a barge’s buoyant force will never be
exceeded. They might build scale models to test the shape, size, and construction materials required to support
the intended cargo.
2. (a) No, the force of the water at the surface is less than the force at 30 m below the surface. With an increase
in depth comes an increase in force. (This increase is caused by the force of gravity acting on the water above
the 30 m mark.)
(b) Engineers made a model of the piers to allow them to analyze problems on a smaller scale. In particular,
they wanted to analyze how ice would affect the piers.
3. (a) Engineers added special products to the concrete to keep it liquid while it was being pumped into the
forms, allowing the forms to be filled completely.
(b) The concrete needed to fill the forms completely to avoid gaps or air pockets, which could weaken the
structure.
CYU 5.4 p. 150
1. (a) It would be difficult to run across a snowy field in running shoes because the area of the running shoes is
insufficient to support the force generated by your mass. The excessive pressure would cause you to sink into
the snow.
(b) Snowshoes provide an increased area to spread your force over. This would reduce the pressure on the
snow and you would not sink.
2. (a)
Note: A pascal is equal to 1 N/m2, so this value cannot be expressed in pascals.
(b)
(c)
3. As the depth of a fluid increases, the effect of gravity acting on the fluid causes an increase in pressure. (The
fluid pressure is directly proportional to the density of the fluid and the depth within the fluid).
4. At an atmospheric pressure of 85 kPa, the hiker is slightly over 1000 m above sea level.
5. The pressure exerted by the person who fell through the ice was
Assuming that 3 N/cm2 is the breaking point of the ice, then the pressure applied by the rescuer would be
It is safe for the rescuer.
CYU 5.5 p. 154
1. The delay observed in the air-filled system resulted from the spaces between the gas particles being reduced
as the gas was compressed. When compared to the same set-up filled with water, no noticeable delay was
observed. After some compression of the gas occurred, the piston in the “receiving” syringe moved. When
compared to the same set-up filled with water, no noticeable delay was observed because the spaces between
the water molecules were much smaller. Effectively, water compresses so little that the first syringe affects the
second syringe almost instantly.
2. The brick will not exert the same force on a desk from its end, side, or base.
Area of the end
=WxH
= 110 cm x 7.6 cm OR = 1.1 m x 0.076 m
= 836 cm2 x 0.0836 m2
Area of the side
=LxH
= 230 cm = 7.6 cm OR
= 2.3 m x 0.076 m
= 1748 cm2 x 0.1748 m2
Area of the base
=LxW
= 230 cm x 110 cm OR
= 2.3 m x 1.1 m
= 25 300 cm2 x 2.53 m2
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Using the formula p = F/A, the force the brick exerts while on its end is
Each surface exerts a different pressure on the desk. The smaller the surface area through which the force is
applied, the greater the resulting pressure is.
3. Liquids are only slightly compressible. For example, oil used as a hydraulic fluid will compress 0.5 % per 6.9
x 106 N/m2 (or 6.9 x 103 kPa). Gases, on the other hand, are compressible.
Here is a sample diagram:
CYU 5.8 p. 163
4. Oil would not be a good fluid in the Jaws of Life because it is flammable and conducts electricity.
5. Roller coasters would probably be possible without hydraulic and pneumatic systems, but they would likely
be far less exciting and less safe.
6. Tunnel-boring machines were developed because they can do the work far faster and more safely than
people digging tunnels by hand.
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CHAPTER 5 REVIEW p. 164
1. (d) 90 N
2. (a) increase
3. (a) F: Viscosity is an important property in the manufacture of chocolate.
(b) T
(c) F: Air pressure decreases with elevation.
(d) F: Car brakes are an example of a hydraulic system.
(e) T
(f) F: Gases are more compressible than liquids.
4. Below are four examples (students are asked to provide three) of fluid knowledge that was used to build the
Confederation Bridge:
• Barges: Barges with the correct buoyancy and, thus, capacity were required to bring out the sections of the
bridge.
• Water and ice: Engineers had to understand the forces that water and ice would exert on the piers and design
the piers to resist these forces.
• Wind: Air deflectors were required to reduce the forces of the wind on vehicles. The bridge structure had to be
streamlined to reduce the forces of the wind on the bridge itself.
• Concrete: To create the massive piers, engineers had to alter the viscosity of the concrete. A longer time was
needed for the concrete to flow in the pumps and pipes before it began to harden. This allowed the concrete to
flow into the massive forms and fill them without there being any gaps in the structure.
5. Five industries in which the properties of fluids play an important role are listed below.
• Heavy machinery: Hydraulic systems lift bulldozer buckets and move tractor blades.
• Automotive: Braking systems are used to stop vehicles.
• Chocolate manufacture: The properties of fluids allow many recipes and shapes to be marketed.
• Hydroelectricity: Water flowing through a turbine generates electricity.
• Ship and airplane design: A ship or airplane must be designed to move smoothly through a fluid and resist the
pressures of the fluid.
• Health: Inoculations require that fluids flow from a syringe through its needle and into a bloodstream.
6. As heat is added to a solid, its particles speed up, breaking the bonds that hold them in position. The
particles are free to move past each other and farther apart. The continued application of heat causes some
liquid particles to burst free from their surface and become a gas. In a gas, the particles move very quickly, with
very large spaces between them.
7. External pressure on a closed air system could cause the collapse of the system if the pressure exceeded
the capacity of the structure or device (e.g., a submarine down too deep). Internally, the gas may compress,
reducing the effectiveness of the system well before it collapses.
8. To reduce air turbulence, the piers, support columns, and spans should be streamlined.
9. Air is removed from a syringe by holding its needle upward, tapping on the side to dislodge any air bubbles,
and then depressing the plunger until some of the fluid (inoculum) is ejected through the needle. This should
remove all the air from inside the fluid in the syringe.
10. (a) At 50 cm x 25 cm, both tanks will contain equal masses of water.
(b) The taller, narrow-based tank exerts its mass over a smaller area and will, therefore, exert greater pressure
on the table.
11. To allow a diver to remain underwater, the tanks contain air under a great deal of pressure. This allows a
small tank to hold considerably more volume. A regulator releases the air in small quantities for the diver.
12. Pushing in the straight stopper will compress the air in the tube, and the stopper will penetrate the tube
some distance. If the tube is filled with water, the stopper will not penetrate any farther because the spaces
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between the water molecules are small enough that water will not compress farther. Alternatively, pushing in
the straight stopper might force the tapered stopper out the other end of the tube because
the force is transmitted through the fluid.
13. (a) With a piston area ratio of 15:1, a force on the smaller piston will be multiplied 15 times.
A force of 1000 N must be exerted on the smaller piston to lift 15 000 N.
(b) With a 15:1 ratio, the distance that the smaller piston must move will be 15 times the distance that the larger
piston moved. 1 m x 15 = 15 m, the small piston must move 15 m to move the large piston 1 m.
14. With two lungs, neither has to work too hard to move a large volume of air in and out for the exchange of
oxygen and carbon dioxide.
15. Aerosol containers are pressurized. They already contain a very large quantity of gas. If the particles
become heated, they begin to move faster and even farther apart. Within the fixed volume of the container, the
rapidly moving particles increase the pressure on the inside of the container. Eventually, the pressure would
cause the can to fail and explode.
16. The air pressure inside a soccer ball increases when the ball is kicked. The force applied by the player’s
foot compresses the flexible cover of the ball, decreasing the volume inside the ball. As the volume decreases,
the pressure must increase. As the ball moves away from the player’s foot, the increased internal pressure
pushes the membrane back into place and this helps to increase the distance the ball will travel.
17. From their experiences, students may respond that hydraulic systems are more effective because hydraulic
fluids are not compressible but respond immediately. Many tool systems are pneumatic, however, and one of
their advantages would be their lighter weight since they are used by mechanics, contractors, and homeowners.
18. The tires would be recalled from the tropical countries first because the higher ambient temperatures could
increase the pressure in an improperly filled tire to beyond a safe margin. The tires could fail even while the car
was at rest in the hot sunlight, let alone as heat builds up in them as they are being used.
19. (a) It is necessary to have space at the top of a jar to allow for expansion.
(b) While the cooking water is boiling, the contents of the jar expand. The space allows for this expansion.
(c) If the lid is sealed before heating, the internal pressure caused by the heating could cause the jar to
explode.
(d) Once the lid is sealed and the jar and its contents cooled, the internal pressure is reduced and a partial
vacuum is created.
(e) The lid “pops” as it is drawn downward by the reduced pressure of the partial vacuum.
(f) Canning is a good way to preserve food because it is simple and inexpensive. Once sealed, the food inside
is free of bacteria. As long as the lid remains “unpopped,” no contamination from the outside can get in. Thus, it
is easy to tell if the food inside is safe.
20. In this situation, pressure is dependent upon depth (h), not on any horizontal distance of the water behind
the dam. The pressure at the base of two identical dams will be the same regardless of the amount of water
behind each.
21. Without hydraulic or pneumatic systems, life would be different in many ways. Some examples are listed
below.
• Lack of heavy-duty machinery for digging or lifting heavy loads would reduce accessibility to many mineral
resources.
• Our ability to construct tall buildings would be limited.
• Automobiles would be more difficult to drive and to stop.
• Many safety features would not exist, such as airbags, ejection seats, and air brakes.
• Portable power tools would be heavier or non-existent.
22. Answers will vary. Problem-solving skills developed in this chapter may include the following:
• writing a question and developing a hypothesis
• controlling variables in experiments
• developing models to explain more complex systems
• using formulas to solve problems
• applying ratios, forces, and distances in confined fluid systems
23. Students’ answers will vary. Knowledge of fluids and fluid power systems will, at least, allow recognition of
these systems in students’ lives and possibly give a better understanding of how some technologies operate.
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