Supplemental Materials The jois of Text Comprehension: Supplementing Retrieval Practice to Enhance Inference Performance by K. Nguyen & M. A. McDaniel, 2015

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 cast-iron. 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.

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?
   
   1. 
      Worn wheel rims
      
   2. 
      Worn brake pads
      
   3. 
      Broke brake calipers
      
   4. 
      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:
   
   1. 
      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.
      
   2. 
      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.
      
   3. 
      The piston in the wheel cylinder has worn down; thus the piston has begun to grind against the disc, resulting in the grinding noise.
      
   4. 
      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?
   
   1. 
      Barometric changes (changes in air pressure)
      
   2. 
      Changes in atmospheric CO₂ levels
      
   3. 
      Changes in atmospheric oxygen levels
      
   4. 
      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?
   
   1. 
      Pressure-modulating valve assembly
      
   2. 
      Booster__Brake_shoe___INFERENCE_MULTIPLE_CHOICE_-_PUMPS'>Electronic controller
      
   3. 
      Booster
      
   4. 
      Brake shoe
      

1. 
   Which type of pump is not classified as a dynamic pump?
   
   1. 
      Gear pump
      
   2. 
      Jet pump
      
   3. 
      Axial-flow pump
      
   4. 
      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?
   
   1. 
      Jet pump
      
   2. 
      Gear pump
      
   3. 
      Sliding vane pump
      
   4. 
      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?
   

b. Centrifuge pump

4. 
   One way that gear and sliding vane pumps differ is that:
   
   1. 
      Gear pumps are dynamic pumps, whereas sliding vane pumps are positive displacement pumps
      
   2. 
      Gear pumps are positive displacement pumps, whereas sliding vane pumps are dynamic pumps
      
   3. 
      Sliding vane pumps transport fluid along the pump wall, whereas gear pumps do not
      
   4. 
      Sliding vane pumps compress the transported fluid, whereas gear pumps do not
      

5. 
   Steel
   
6. 
   Iron
   
7. 
   Titanium
   
8. 
   Silicon
   

2. 
   Most cars have:
   
   1. 
      Drum brakes on all four wheels
      
   2. 
      Disc brakes on the front wheels and drum brakes on the rear wheels
      
   3. 
      Disc brakes on all four wheels
      
   4. 
      Drum brakes on the front wheels and disc brakes on the rear wheels
      

2. 
   Most buses have which type of brakes?
   
   1. 
      Air brakes
      
   2. 
      Disc brakes
      
   3. 
      Drum brakes
      
   4. 
      Mechanical brakes
      

2. 
   Which of the following is not a component of a disc brake?
   
   1. 
      Brake pads
      
   2. 
      Cable
      
   3. 
      Caliper
      
   4. 
      Piston
      

2. 
   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?
   
   1. 
      Levers
      
   2. 
      Cables
      
   3. 
      Calipers
      
   4. 
      Rods
      

2. 
   What part of the brake physically stops a wheel from spinning?
   
   1. 
      The caliper
      
   2. 
      The brake pad
      
   3. 
      The cylinder
      
   4. 
      The drum
      

2. 
   Which of the following is a component of a hydraulic brake system?
   
   1. 
      U-shaped caliper
      
   2. 
      Electronic controller
      
   3. 
      Compressor
      
   4. 
      Master cylinder
      

2. 
   The device that applies additional pressure to the master cylinder piston in a power-assisted brake system by using the difference in pressure between the surrounding atmosphere and the vacuum in the engine is called a:
   
   1. 
      Caliper
      
   2. 
      Enhancer
      
   3. 
      Diaphragm
      
   4. 
      Booster
      

5. 
   Sliding vanes rotate by the inlet port to move fluid.
   
6. 
   The distance between the pump wall and the impeller narrows near the outlet port.
   
7. 
   Fluid becomes pressurized in the pump.
   
8. 
   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?
   
   1. 
      Motor oil
      
   2. 
      Water
      
   3. 
      Paint
      
   4. 
      Syrup
      

2. 
   Which statement about axial-flow pumps is true?
   
   1. 
      Axial-flow pumps are not as efficient as centrifuge pumps.
      
   2. 
      Axial-flow pumps have motor-driven rotors.
      
   3. 
      Air leaves the axial-flow compressor under low pressure.
      
   4. 
      Fluid in axial-flow pumps flows in a circular pattern.
      

2. 
   Which of the following is not an alternative name for gas pumps?
   
   1. 
      Exhausters
      
   2. 
      Blowers
      
   3. 
      Fans
      
   4. 
      Compressors
      

2. 
   Electromagnetic pumps are often used:
   

b. In deep water wells

c. In chemical-processing plants and refineries

d. In nuclear reactors

2. 
   The lobes in a lobe pump are controlled by:
   
   1. 
      Pressure of the fluid
      
   2. 
      A central piston
      
   3. 
      External timing gears
      
   4. 
      High-velocity fluid
      

2. 
   Upon what principle do jet pumps operate?
   
   1. 
      A high viscosity fluid will carry along any other fluid it passes through
      
   2. 
      A high density fluid will carry along any other fluid it passes through
      
   3. 
      A high velocity fluid will carry along any other fluid it passes through
      
   4. 
      A high pressure fluid will carry along any other fluid it passes through
      

2. 
   Centrifugal pumps are:
   
   1. 
      Expensive
      
   2. 
      Commonly used for the transportation of food products
      
   3. 
      Driven by a vacuum
      
   4. 
      Able to handle large amounts of fluid
      

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?

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?