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Supplemental Materials
The JOIs of Text Comprehension: Supplementing Retrieval Practice to Enhance
Inference Performance
by K. Nguyen & M. A. McDaniel, 2015, JEP: Applied
http://dx.doi.org/10.1037/xap0000066
BRAKES
A brake is a device that slows a moving object. A brake is a device that stops a
moving object. Most brakes have a part called a brake pad or brake shoe. The brake
pad/brake shoe presses against a turning wheel or a unit connected to the wheel to
produce friction. This friction converts the wheel’s energy of motion to heat, thus
slowing or stopping the wheel. Vehicles and industrial machines use a wide variety of
brakes. This article describes brakes used chiefly in vehicles. Vehicles are equipped with
three major kinds of brakes: mechanical brakes, hydraulic brakes, and air brakes.
Mechanical brakes have levers or cables that force one or two pads against the
wheel. Most bicycles have two mechanical brakes called caliper brakes, one caliper brake
for each wheel. Each brake has two small rubber pads, one rubber pad on each side of the
wheel rim. The pads are mounted on a mechanical device that is connected to one end of
a long cable. The other end of the cable is connected to a lever on the handlebar. When
the rider squeezes this lever, force on the cable presses the pads against the wheel rim.
Automobiles are equipped with another kind of mechanical brake called an emergency
brake or a hand brake. This brake is also known as a parking brake. It is known as a
parking brake because it helps prevent a parked car from rolling away. When the driver
applies the emergency brake, a system of levers, rods, and cables applies pressure to the
pads or shoes of the rear wheels.
Hydraulic brakes use a special liquid called brake fluid. Brake fluid is used to
apply brake pressure to pads or shoes. Most automobiles have a hydraulic braking
system. The main parts of this system are a chamber called a master cylinder. The master
cylinder is located near the brake pedal. At least one wheel cylinder is located at each
wheel. Tubes called brake lines connect the master cylinder to the wheel cylinders. The
cylinders and brake lines are filled with brake fluid.
Inside the master cylinder is a piston. This piston can slide back and forth. In a
simple hydraulic system, the brake pedal controls this piston by means of a rod or some
other mechanical link. When the driver pushes on the pedal the piston inside the master
cylinder exerts pressure on the fluid…and slides forward a short distance. The fluid
transmits this pressure through the brake lines. This pressure forces pistons in the wheel
cylinders to move forward. As the wheel cylinders move onward they apply brake
pressure to pads or shoes. The wheel cylinders are mounted in either disc brakes or drum
brakes. Most cars have disc brakes on the front wheels. Most cars have drum brakes on
the rear wheels.
Disc brakes have a disc which is usually made of cast iron. The disc is attached to
the vehicle’s axle. The wheel is attached to the disc. A U-shaped caliper assembly fits
around a part of the disc. The U-shaped caliper does not rotate with the disc. This
assembly includes one or two wheel cylinders. Each wheel cylinder contains a piston.
Each wheel cylinder contains two brake pads. There is one brake pad on each side of the
disc. The brake pads are flat pieces of metal. The flat pieces of metal are linked with a
heat resistant material. When the brake is applied, the pads press inward against the disc.
Drum brakes have a drum fastened to the axle. The drum is usually made of castiron. The wheel is attached to the drum. Inside the drum are two semicircular brake
shoes. The brake shoes are lined with a heat resistant material. The shoes do not rotate
with the drum. Between the shoes is a wheel cylinder. The cylinder has two pistons. The
two pistons push in opposite directions. One piston pushes against each shoe. When the
brake is applied the shoes press outward against the drum.
Power-assisted brakes provide additional brake pressure. Power-assisted brakes
are found in most automobiles. A device called a booster is mounted between the brake
pedal and the master cylinder. When the driver steps on the pedal the booster uses the
difference in pressure between the vacuum in the engine and the surrounding atmosphere
to apply additional pressure to the piston in the master cylinder. Antilock-brake systems
are installed in some automobiles. Antilock brake systems prevent wheels from locking
and skidding on wet or icy roads. An anti-lock brake system (ABS) includes a sensor at
each wheel. An antilock brake system includes a tiny computer called an electronic
controller. A device known as a pressure-modulating valve assembly is mounted between
the master cylinder and the wheel cylinders. Electric wires connected the sensors to the
controller. Electric wires connect the controller to the valve assembly. The sensors send
electric signals that represent wheel speed to the electronic controller. When a sensor
indicates that a wheel is locking the controller transmits a signal. The signal is
transmitted to the valve assembly. The assembly, in turn, applies pulses of brake
pressure. The pulses of brake pressure are applied to the brake of the locked wheel. This
pressure alternately applies and releases the brake. Pulsing continues until the wheel
rotates normally. Traction control prevents the wheels from slipping. Traction control is
available in some cars with antilock brakes. When a sensor indicates slippage, the
electronic controller applies brake pressure to the slipping wheel. If more than one wheel
is slipping, the controller reduces engine power. Engine power is reduced until the wheels
stop slipping.
Air brakes use compressed air. The compressed air is supplied by a machine
called a compressor. Most buses have air brakes. Most heavy trucks have air brakes.
Trains have air brakes. When the driver or engineer applies the brakes, a storage unit
releases compressed air. The air pushes against a piston or diaphragm. The
piston/diaphragm applies brake pressure to pads or shoes. Buses and trucks have disc and
drum brakes. The disc and drum brakes in buses and trucks are like those in automobiles.
In trains, shoes press against the outside of the wheel.
PUMPS
A pump is a device that moves liquids and gases. Pumps are used in a variety of
machines and other devices, including home heating systems, refrigerators, oil wells,
water wells, turbojet engines, and automobile engines. The fluids that are moved by
pumps range from air for inflating bicycle tires to liquid sodium and liquid potassium,
which are used for cooling nuclear reactors. Most pumps are made of steel, but some
pumps are made of glass or plastic. Gas pumps are also called compressors, fans, or
blowers. The two main types of pumps are dynamic pumps and positive displacement
pumps. Dynamic pumps maintain a steady flow of fluid. Positive displacement pumps, on
the other hand, trap individual portions of fluid in an enclosed area before they are
moved.
DYNAMIC PUMPS
Centrifuge pumps consist of a motor-driven propeller-like device, called an impeller. The
impeller is contained within a circular housing, and it is a wheel of curved blades that
rotates on an axis. Before most centrifugal pumps can start pumping liquid, they must be
primed (filled with liquid). As the impeller rotates, it creates suction, which draws a
continuous flow of fluid through an inlet pipe. Fluid enters the pump at the center of the
impeller and then travels out along the blades due to centrifugal (outward) force. The
curved ends of the blades then sweep the fluid to an outlet port. Centrifugal pumps are
inexpensive, and they can handle large amounts of fluid. Centrifugal pumps are widely
used in chemical-processing plants and oil refineries.
Axial-flow pumps have a motor-driven rotor that directs fluid along a path parallel to its
axis. The fluid thus travels in a relatively straight path from the inlet pipe through the
pump to the outlet pipe. Axial-flow pumps are most often used as compressors in turbojet
engines. Centrifugal pumps are sometimes used for this purpose, but axial-flow pumps
are more efficient. Axial-flow compressors have alternating rows of rotors and stationary
blades that produce a pressure rise in the air as it moves through the axial-flow
compressor. Air then leaves the compressor under high pressure.
Jet pumps get their name from the way they move fluid. These pumps operate upon the
principle that a high-velocity fluid will carry along any other fluid it passes through. Most
jet pumps send a jet stream of water through the fluid that needs to be moved. The jet
carries the fluid into the outlet pipe and creates a vacuum that draws more fluid into the
pump. The amount of fluid that is carried out of most jet pumps is several times the
amount of fluid that is in the jet itself. Jet pumps can be used to raise water from wells
that are deeper than 200 feet. In such cases, a centrifugal pump at ground level supplies
water for a jet at the bottom of the well. The jet carries well water with it back up to the
ground level. Jet pumps are also used in high-vacuum diffusion pumps to create a
vacuum in an enclosed area.
In high-vacuum diffusion pumps, a high-velocity jet of mercury or oil vapor is sent into
the enclosed area. The vapor molecules collide with the molecules of air, and the
collision forces the vapor molecules out the outlet port. Electromagnetic pumps are used
chiefly to move liquid sodium and liquid potassium, which serve as coolants in nuclear
reactors. Electromagnetic pumps consist of electrical conductors and magnetized pipes.
The conductors send current through the fluid, making the fluid an electromagnet. The
fluid is then moved by the magnetic attraction and repulsion (pushing away) between the
fluid’s magnetic field and magnetic field of the pipes. The fluid is moved in an
electromagnetic pump much in the way an armature is moved in an electric motor.
POSITIVE DISPLACEMENT PUMPS
Rotary pumps are the most widely used positive displacement pumps. They are often
used to pump such viscous (sticky) liquids as motor oil, syrup, and paint. The basic
concept behind rotary pumps is that they use rotating elements to trap liquid in the
suction side of the pump and force it into the discharge side. There are three main types
of rotary pumps: gear pumps, lobe pumps, and sliding vane pumps. Gear pumps consist
of two gears that rotate against the walls of a circular housing. There are inlet and outlet
ports at opposite sides of the housing. The ports are on line with the point where the teeth
of the gears are fitted together. The smaller gear is called the idler gear and the larger
gear is called the rotor gear. As the idler gear rotates around a stationary pin, it turns the
rotor gear. Fluid that enters the pump is trapped by the rotating gear teeth, which sweep
the fluid along the pump wall to the outlet port.
Lobe pumps operate in a manner similar to gear pumps, but lobe pumps have no gears.
Lobe pumps are equipped with impellers that have lobes (rounded projections) fitted
together. The lobes, however, do not touch each other like gear teeth do. The lobes are
controlled by external timing gears. Since the lobes do not come in contact with each
other, there is no metal-to-metal wear over time. The large distance between lobes means
that larger particles can be used in these pumps, but they do not perform well with low
viscosity liquids. Lobe pumps can discharge large amounts of fluid and can discharge
fluid at low pressure levels.
Sliding vane pumps consist of a slotted impeller that is mounted off-center in a circular
housing. Sliding vanes (blades) move in and out of the slots. As the vanes rotate by the
inlet port, they sweep up fluid and trap it against the pump wall. The distance between the
impeller and the pump wall narrows near the outlet port. As the fluid is carried around to
this port, the vanes are pushed in and the fluid is compressed. The pressurized fluid then
rushes out the outlet port.
INFERENCE MULTIPLE CHOICE - BRAKES
1. Your sister’s bicycle has a caliper brake system. When she pulls the brake on the
handlebar the bike does not slow down at all. The bike doesn’t even make any
unfortunate noises, such as a grinding or squealing noise. Which of the following
problems is most likely?
a. Worn wheel rims
b. Worn brake pads
c. Broke brake calipers
d. Broken brake cable
2. Your friend tells you that he thinks that his car’s disc brakes are wearing out, as he
hears a grinding noise each time he presses the brake pedal. A likely explanation is
that:
a. The heat resistant material on the brake pads has worn away; thus when
the pads press inward against the disc the metal pad grinds against the
metal disc.
b. The U-shaped caliper assembly has worn down; the caliper assembly no
longer rotates in sync with the disc and is thus emitting the grinding noise.
c. The piston in the wheel cylinder has worn down; thus the piston has begun to
grind against the disc, resulting in the grinding noise.
d. The heat resistant material on the brake shoe has worn away; thus when the
shoes press outward against the disc the metal shoe grinds against the metal
disc.
3. Recently a small, intelligent microbial colony has settled inside your car’s disc brake
system. Each time you press the brake pedal these clever microbes note which type
of atmospheric change?
a. Barometric changes (changes in air pressure)
b. Changes in atmospheric CO2 levels
c. Changes in atmospheric oxygen levels
d. Temperature changes
4. Your fancy new car includes both an antilock brake system and a traction control
system. After owning the car for a few months you realize that your brakes are still
working, but neither of these systems seems to be functioning. Failure of which of
the following components is most likely to cause this problem?
a. Pressure-modulating valve assembly
b. Electronic controller
c. Booster
d. Brake shoe
INFERENCE MULTIPLE CHOICE - PUMPS
1. Which type of pump is not classified as a dynamic pump?
a. Gear pump
b. Jet pump
c. Axial-flow pump
d. Electromagnetic pump
2. Pump X has been used to transport fluid between holding tanks. The pump required
a small amount of fluid to begin running and has transported a large amount of fluid
in return. One component of the pump is large impeller. What type of pump is pump
X?
a. Jet pump
b. Gear pump
c. Sliding vane pump
d. Centrifuge pump
3. The beverage company that you work for needs a pump in order to move W.U.C.
Root Beer between its two new holding tanks. Since business is booming you will
need to move lots of root beer, and cost in not an issue. However, it will not be
necessary to maintain a steady flow of fluid, as only a portion of the root beer will be
moved at any given time. Additionally it will be necessary to keep pressure within
the tanks at a low level, so as to not spoil the product. Given the following options,
which type of pump do you recommend to the company?
a. Jet pump
b. Centrifuge pump
c. Electromagnetic pump
d. Lobe pump
4. One way that gear and sliding vane pumps differ is that:
a. Gear pumps are dynamic pumps, whereas sliding vane pumps are positive
displacement pumps
b. Gear pumps are positive displacement pumps, whereas sliding vane pumps
are dynamic pumps
c. Sliding vane pumps transport fluid along the pump wall, whereas gear pumps
do not
d. Sliding vane pumps compress the transported fluid, whereas gear pumps
do not
FACTUAL MULTIPLE CHOICE - BRAKES
1. The “Drum” in a drum brake is usually made of:
e. Steel
f. Iron
g. Titanium
h. Silicon
2. Most cars have:
a. Drum brakes on all four wheels
b. Disc brakes on the front wheels and drum brakes on the rear wheels
c. Disc brakes on all four wheels
d. Drum brakes on the front wheels and disc brakes on the rear wheels
3. Most buses have which type of brakes?
a. Air brakes
b. Disc brakes
c. Drum brakes
d. Mechanical brakes
4. Which of the following is not a component of a disc brake?
a. Brake pads
b. Cable
c. Caliper
d. Piston
5. A car’s hand brake uses a complex mechanical system to apply pressure to the pads
or shoes of the rear wheels. Which of the following is not a component of that
system, as mentioned in the article?
a. Levers
b. Cables
c. Calipers
d. Rods
6. What part of the brake physically stops a wheel from spinning?
a. The caliper
b. The brake pad
c. The cylinder
d. The drum
7. Which of the following is a component of a hydraulic brake system?
a. U-shaped caliper
b. Electronic controller
c. Compressor
d. Master cylinder
8. The device that applies additional pressure to the master cylinder piston in a powerassisted brake system by using the difference in pressure between the surrounding
atmosphere and the vacuum in the engine is called a:
a. Caliper
b. Enhancer
c. Diaphragm
d. Booster
FACTUAL MULTIPLE CHOICE - PUMPS
1. Which is NOT true about sliding vane pumps?
e. Sliding vanes rotate by the inlet port to move fluid.
f. The distance between the pump wall and the impeller narrows near the outlet
port.
g. Fluid becomes pressurized in the pump.
h. The impeller is mounted in the center of a circular housing.
2. Rotary pumps are least likely to be used to pump which of the following substances?
a. Motor oil
b. Water
c. Paint
d. Syrup
3. Which statement about axial-flow pumps is true?
a. Axial-flow pumps are not as efficient as centrifuge pumps.
b. Axial-flow pumps have motor-driven rotors.
c. Air leaves the axial-flow compressor under low pressure.
d. Fluid in axial-flow pumps flows in a circular pattern.
4.
Which of the following is not an alternative name for gas pumps?
a. Exhausters
b. Blowers
c. Fans
d. Compressors
5. Electromagnetic pumps are often used:
a. In shallow water wells
b. In deep water wells
c. In chemical-processing plants and refineries
d. In nuclear reactors
6. The lobes in a lobe pump are controlled by:
a. Pressure of the fluid
b. A central piston
c. External timing gears
d. High-velocity fluid
7. Upon what principle do jet pumps operate?
a. A high viscosity fluid will carry along any other fluid it passes through
b. A high density fluid will carry along any other fluid it passes through
c. A high velocity fluid will carry along any other fluid it passes through
d. A high pressure fluid will carry along any other fluid it passes through
8. Centrifugal pumps are:
a. Expensive
b. Commonly used for the transportation of food products
c. Driven by a vacuum
d. Able to handle large amounts of fluid
PROBLEM SOLVING QUESTIONS - BRAKES
1) EXPERIMENT 1: Why do brakes get hot?
EXPERIMENT 2: You recently got a new bike and decided to take it for a test
ride on some local trails. The trail has a steep hill, and you start to go too fast.
You brake hard and manage to slow down and finally stop shortly after reaching
the bottom. You inspect your new bike and notice the brakes are warm. Should
you be concerned that something is wrong with your bike or is it normal for
brakes to get hot? If not, explain why not. If so, describe the process that occurs
on your bike that causes this to happen.
2) EXPERIMENT 1: Suppose that you press on the brake pedal in your car but the
brakes don’t work. What could have gone wrong?
EXPERIMENT 2: Suppose that you press on the brake pedal in your car but the
brakes don’t work. What are 4 things that could have gone wrong in your car?
3) EXPERIMENT 1: What happens when you pump the brakes (i.e. press the pedal
and release the pedal repeatedly and rapidly)? Why might this be a good idea if
you’re driving an older car?
EXPERIMENT 2: You have an older car that does not have an antilock braking
system, and you notice your wheels have begun to lock occasionally. What is
something you could manually do when you brake to prevent the wheels from
locking? How does this process work?
4) EXPERIMENT 1: What are some ways that a car’s brake system might be
improved to make the system more efficient, that is, to reduce the distance needed
to stop?
EXPERIMENT 2: You are an engineer, and you need to design a new brake
system that is more efficient, meaning that the car will need less distance to come
to a complete stop. What are two things that you could do to improve the system?
PROBLEM SOLVING QUESTIONS - PUMPS
1) EXPERIMENT 1: The well at your grandparents’ cottage is run using a jet pump.
However, it has become less efficient as of late (that is, it hasn’t been moving the
water as rapidly). What could be done to make the jet pump more efficient?
EXPERIMENT 2: The well at your grandparents’ cottage is run using a jet pump.
However, it has become less efficient as of late (that is, it hasn’t been moving the
water as rapidly). What are two problems that might be causing problems with
the jet pump?
2) EXPERIMENT 1: Centrifugal and Axial-flow pumps are similar. However, there
are times when one or the other is preferable. Under what circumstances might
centrifugal pumps be preferable? Under what circumstances might Axial-flow
pumps be preferable?
EXPERIMENT 2: You have a new client who’s trying to decide between
centrifugal and axial-flow pumps. He doesn’t have a lot of money and wants to
transport a lot of petroleum. Which pump do you recommend and give 2 reasons
why? What level of pressure does this pump need to move the fluid?
3) EXPERIMENT 1: Why is a gear pump better than a centrifugal pump for
pumping viscous or sticky liquids?
EXPERIMENT 2: You and your intern are working on constructing a pump for a
new client. This pump needs to be able to transport viscous or sticky liquids. Your
intern has narrowed the choice down to centrifugal pumps and gear pumps.
Which pump do you tell her is better and why?
4) EXPERIMENT 1: Why is it necessary that the pipes in an electromagnetic pump
be appropriately magnetized? What problems might the pump have if the pipes
weren’t magnetized?
EXPERIMENT 2: Oh no! One of your client’s electromagnetic pumps’
magnetization has gone awry. Why is it necessary that the pipes in this pump be
appropriately magnetized? What problems does your client report experiencing?