Mechanical Aptitude for Firefighter Exam Study Guide

What Is a Mechanical Device?

A mechanical device is a tool designed to make a given task easier. For example, you could drive a nail into a piece of wood with a rock. However, a long time ago, someone who spent a lot of time building things with wood figured out that it would be a lot more efficient to use something that was easier to hold on to than a rock. He or she thought that a long slender handle might be nice, and that a hard piece of metal for striking the nail would provide more accuracy and not damage the wood as easily. Thus, the hammer was born.

Most mechanical devices were invented in the same manner: People looking for easier ways to perform their everyday jobs. Some mechanical devices are thousands of years old, such as the lever, the wheel, and many hand tools. Other more complex devices, such as pumps and valves, were invented more recently. Many times, the idea of a new mechanical device exists but the technology to make it does not. For example, many years before the pump was invented, people probably discussed the need for an easier way to move water from the river to the town on the hill. However, the technology for casting metal had not yet been invented, so the pump could not possibly have been invented at that time.

Mechanical devices cover a wide range of types of tools. In general, they are tools that relate to physical work and are governed by mechanical forces and movements. You can usually see what they do and how they work—as opposed to, say, a light switch or a battery, which are electrical devices. Some tools are used to directly accomplish a specific task, as when you use a hand saw to cut a piece of wood. Others, such as pulleys and gears, may be used indirectly to accomplish certain tasks that would be possible without the device but are easier with it. Still others, such as gauges, only provide feedback information on the operation of other mechanical devices. You see and use mechanical devices many times each day, so there is no reason to be intimidated by a mechanical aptitude section on the exam.

Commonly Tested Mechanical Devices

The following sections review some of the mechanical devices that are most likely to appear on firefighter exams.

Hand Tools

Hand tools are defined as tools operated not by motors but rather by human power. There are many different types of hand tools, including carpentry tools, automotive hand tools, and hand tools used specifically by firefighters. This chapter cannot cover every conceivable hand tool, so it will be limited to tools used in everyday situations and those specific to firefighting—the ones you are most likely to be tested on.

Some of the hand tools used by carpenters and other workers, including firefighters, are listed in the table below, along with their most common uses and some examples of each kind.

Hand tools used in the fire and rescue service are often classified by their main function or their size. In general, a large hand tool would not fit in a standard tool box, whereas a small hand tool would. Most fire apparatus carries a supply of standard, everyday small hand tools such as wrenches, screwdrivers, and hammers. These tools are used for a variety of purposes. For example, if a fire occurs in an electrical breaker box, firefighters will need wrenches or screwdrivers to disassemble the box to check if the fire is out.

Many common larger hand tools have uses in the fire service. Automotive jacks and high-lift jacks are used in vehicle rescue to stabilize cars and trucks. Sledgehammers are used in forcible entry as well as in other applications. Tools such as axes and ladders have obvious uses in the fire service, although the versions of these tools used for fire service are typically heavier or have greater capacity than domestic models. For example, fire service ladders have much greater capacity than a ladder you may have in your home, and are much heavier.

Specialty tools are often classified by the main function they serve. Some examples are pulling tools such as hooks or pike poles, and prying tools such as pry bars. Some tools also have secondary uses. An axe is normally used for cutting; however, a flat-head axe can also be used as a striking tool to drive another tool.

Gears

A gear is generally a toothed wheel or cylinder that meshes with another toothed element to transmit motion or to change speed or direction. Gears are typically attached to a rotating shaft turned by an outside energy source such as an electric motor or an internal combustion engine. Gears are used in many mechanical devices, including automotive transmissions, carpenter's hand drills, elevator lifting mechanisms, bicycles, and carnival rides such as Ferris wheels and merry-go-rounds.

Gears can be used in several different configurations. Two gears may be connected by directly touching each other, as in an automotive transmission. In this arrangement, one gear spins clockwise and the other rotates counterclockwise. Another possible configuration is to have two gears connected by a loop of chain, as on a bicycle. In this arrangement, the first gear rotates in one direction, causing the chain to move. Because the chain is directly connected to the second gear, the second gear will immediately begin to rotate in the same direction as the first gear.

Many times a system will use two gears of different sizes, as on a ten-speed bicycle. This will allow changes in speed of the bicycle or machine.

Problems about gears will always involve rotation or spinning. The easiest way to approach test questions that involve gears is to draw a diagram of what the question is describing, if one is not already provided. Use arrows next to each gear to indicate which direction (clockwise or counterclockwise) it is rotating.

Pulleys

A pulley consists of a wheel with a grooved rim in which a pulled rope or cable is run. Pulleys are commonly used with ropes or steel cable to change the direction of a pulling force or to add mechanical advantage.

Pulleys are often used to lift things. For instance, a pulley could be attached to the ceiling of a room. A rope could be run from the floor, up through the pulley, and back down to a box sitting on the floor. The pulley would allow you to pull down on the rope and cause the box to go up. That is, the pulley causes a change in direction of the pulling force.

Another common use for a pulley is to connect an electric motor to a mechanical device such as a pump. One pulley is placed on the shaft of the motor, and a second pulley is placed on the shaft of the pump. A belt is used to connect the two pulleys. When the motor is turned on, the first pulley rotates and causes the belt to rotate, which in turn causes the second pulley to rotate and turn the pump. This arrangement is very similar to the previous example of a bicycle chain and gears.

You may have seen pulleys used in a warehouse to lift heavy loads. Another use for a pulley is on a large construction crane. The cable extends from the object being lifted up to the top of the crane boom, across a pulley, and back down to the electric winch that is used to pull on the cable. In this situation, the pulley again causes a change in direction of the pulling force, from the downward force of the winch that pulls the cable to the upward movement of the object being lifted.

Levers

A lever is a very old mechanical device. A lever typically consists of a metal or wooden bar that pivots on a fixed point. The object of using a lever is to gain a mechanical advantage. Mechanical advantage results when you use a mechanical device to make a task easier; that is, you gain an advantage by using a mechanical device. A lever allows you to complete a task, typically lifting, that would be more difficult or impossible without the lever.

The most common example of a lever is a playground seesaw. A force (a person's weight) is applied to one side of the lever, which causes the weight on the other side (the other person) to be lifted. However, since the pivot point on a seesaw is in the center, each person must weigh the same or things do not work well. A seesaw is a lever with no mechanical advantage. If you push down on one side with a weight of 10 pounds, you can only lift a maximum of 10 pounds on the other side. This is no great advantage.

This brings us to the secret of the lever: To lift an object that is heavier than the force you want to apply to the other side of the lever, you must locate the pivot point closer to the object you want to lift. If two 50- pound children sit close to the center of the seesaw, one 50-pound child close to the end of the board on the other side will be able to lift them both.

Test questions about levers will typically require a bit of math (multiplication and division) to solve the problem. There is one simple concept that you must understand to solve lever problems: The product of the weight to be lifted times the distance from the weight to the pivot point must be equal to the product of the lifting force times the distance from the force to the pivot point. Stated as an equation: w × d₁ = f × d₂.

For example, Bill has a 15-foot long lever, and he wants to lift a 100-pound box. If he locates the pivot point 5 feet from the box, leaving 10 feet between the pivot point and the other end of the lever where he will apply the lifting force, how hard must he press on the lever to lift the box?

Use the lever formula, w × d₁ = f × d₂.The weight of 100 pounds times 5 feet must equal 10 feet times the force: 100 × 5 = 10 × force. Using multiplication and division to solve for the force, you get 50 pounds of force that Bill must apply to the lever to lift the box.

Fasteners

A mechanical fastener is any mechanical device or process used to connect two or more items together. Typical examples of fastening devices are bolts, screws, nails, and rivets. Processes can be used to mechanically join items together, including gluing and welding. There are also unique mechanical fasteners such as "hook and loop," which consist of two tapes of material with many small plastic hooks and loops that stick together. Hook and eye fastening tape—Velcro©—is the most common fastener used on firefighters' turnout gear, part of the complete personal protective equipment that protects firefighters from exposure to the products of combustion.

Springs

A spring is an elastic mechanical device, normally a coil of wire, that returns to its original shape after being compressed or extended. There are many types of springs, including the compression coil, spiral coil, flat spiral, extension coil, leaf spring, and torsional spring.

Springs are used for many applications such as car suspensions (compression coil and leaf springs), garage doors (extension coil and torsion springs), wind-up clocks (flat spiral and torsion springs), and some styles of ballpoint pens (compression coil).

In the kinds of questions you are likely to be asked on the firefighter exam, you can assume that springs behave linearly. That is, if an extension spring stretches one inch under a pull of ten pounds, then it will stretch two inches under a pull of 20 pounds. In real life, if you pull too hard on a spring, it will not return to its original shape. This is called exceeding the spring's elastic limit. Your exam is not likely to deal with this type of spring behavior.

If several springs are used for one application, they can be arranged in one of two ways—in series or in parallel. The easiest way to remember the difference is that if the springs are all hooked together, end to end, then you have a series of springs. The other option is for the springs not to be hooked together but to be lined up side by side, parallel to each other. If two springs are arranged in series, they will stretch much farther than the same two springs arranged in parallel under the same pulling force. This is because in series, the total pulling force passes through both springs. If the same springs are arranged in parallel, the pulling force is divided equally with half going through each spring.

The key to solving spring problems is to draw a diagram of the arrangement, if one isn't already provided, and follow the pulling force through the system.

Valves

A valve is a mechanical device that controls the flow of liquids, gases, or loose material through piping systems. There are many types of valves, including butterfly valves, gate valves, plug valves, ball valves, and check valves.

A valve is basically a gate that can be closed or opened to permit the fluid or gas to travel in a particular direction. The type of exam question you are likely to see that involves valves will be one in which you must follow a piping flow diagram through several sets of valves. These problems are best approached by taking your time and methodically following each branch of the piping system from start to finish.

Gauges

Gauges are used to monitor the various conditions and performance of mechanical machines such as pumps and internal combustion engines, as well as to monitor the surrounding atmospheric conditions, which could indirectly affect a particular machine.

Gauges are usually marked with the units they are measuring. A few examples of different types of units are:

• degrees Celsius or Fahrenheit for temperature gauges
• pounds per square inch (psi) for pressure gauges
• meters (or sometimes feet) for elevation gauges

You must be very careful to recognize and understand the units of a gauge that appear in a test question. For instance, a temperature gauge (commonly called a thermometer) could use either degrees Fahrenheit or degrees Celsius. Mistakes on units can cause major problems, so be careful! The table on page 200 shows some common types of gauges, what they measure, and the kind of units they use.

Gauges are sometimes marked with warnings about limits of safe operation. Most gauges on fire apparatus are now color coded, and many newer pieces of apparatus are equipped with digital gauges with audible warnings. For instance, an oil pressure gauge on an internal combustion engine may show a maximum safe working pressure of 15 psi. If you are asked about the safe operation of a device with a gauge on it, you should pay careful attention to any markings that show such a limit.

Pumps

A pump is a device used to transfer a liquid or a gas from one location, through a piping system, to another location. For example, a fire engine is a large, self-propelled pump capable of delivering a large volume of water at varying pressures. There are many different types of pumps, including centrifugal pumps, positive displacement pumps, metering pumps, diaphragm pumps, and progressive cavity pumps.

Generally speaking, a working pump consists of the pump itself (case, bearings, impeller, seals, shaft, base, and other components) and an outside energy source. The outside energy source could be an electric motor, internal combustion engine, or battery to provide mechanical energy to the pump. This energy causes the inner workings of the pump to propel the liquid or gas through the piping system. The flow rate at which the liquid or gas is pushed through the piping system is typically measured by a flow meter in units of gallons per minute (gpm) or cubic feet per minute (cfm).

Pumps are used for many purposes. Additional examples include gasoline pumps used to pump the gasoline from a holding tank into your car, water pumps to transfer drinking water from a reservoir to your house or business, and industrial pumps used to move industrial fluids such as chemicals or waste products from one tank to another inside a plant. A car also uses pumps to pump fuel from the gas tank to the engine and to pump coolant from the radiator to the engine block.

Systems That Use Mechanical Devices

Many mechanical devices are actually a combination of several simple devices that work in conjunction to form a group of interacting mechanical and electrical components called a system. Some of the systems most likely to appear on the exam are discussed below.

Internal Combustion Engines

Internal combustion engines (ICEs) are commonly used to drive many mechanical devices. However, they are very complex mechanical devices themselves. ICEs are used in cars, trucks, construction equipment, and many other devices. They can be fueled by gasoline, diesel fuel, natural gas, or other combustible fossil fuels.

An ICE is a system composed of dozens of individual mechanical (as well as electrical) systems. A few of the major systems within an ICE are discussed below.

The Cooling System

The purpose of the cooling system is to dissipate the heat generated by the engine. The system consists of a pump that moves the coolant from the radiator through piping to the engine block, where it becomes hot, and then back out to the radiator where the liquid coolant is cooled.

The Pistons, Tie Rods, and Crankshafts

The pistons, tie rods, and crankshafts are all parts of the inner workings of an ICE. In a gasoline-powered engine, a spark plug ignites the fuel and air mixture inside the cylinder, forcing the piston down. In a diesel engine, the ignition of the fuel is caused by the heat of compression of the air in the cylinder. At just the right time in the cycle, fuel is injected into the cylinder, causing an explosion that forces the piston down. In both types of engines, the piston is mechanically linked to a tie rod, which in turn is linked to a crankshaft. The up-and-down motion of the cylinder is changed into a rotational movement by the crankshaft. The crankshaft drives a transmission, which is a gear box. The transmission sends the power developed by the engine to the wheels of the vehicle, the workings of the pump, or whatever device the ICE is powering. Diesel power is the most common ICE installed in fire apparatus.

The Fuel Pump

Fuel, usually gasoline or diesel fuel, is transferred to the engine from the fuel tank (or tanks) by this pump, which is either a mechanically driven device or, as is now more common, electrically driven. The fuel pump delivers fuel to a carburetor (gasoline) or fuel injection system (diesel and newer gasoline engines), which distribute the fuel under pressure in a spray to the proper cylinder. Many devices that were formerly mechanically driven are now replaced by computer controlled devices.

The Throttle Governor

A throttle governor is a mechanical or electronic device that is used to control the speed of an ICE. In older motor vehicles, it is a spring device that works directly on the gas pedal. In more modern motor vehicles, it is an electronic device that limits the speed of the engine. A throttle governor can be used to limit or maintain the vehicle's speed and, on fire apparatus, to maintain speed at a set rate when the vehicle is used to power pumps, hydraulics, or operate auxiliary machinery when stationary.

Motor Vehicles

Motor vehicles are among the most complex assemblies of mechanical and electronic devices in existence. A piece of fire apparatus is among the most complex of all motor vehicles with hydraulic systems, power systems, pumps, compressed air, and lighting systems, to name a few. Today, computers have taken over more and more of the work that had previously been done by mechanical devices. All of these systems operate in addition to the normal subsystems discussed next.

The Brakes

Motor vehicle brakes can be of several types. Originally, brakes were mechanical, using direct pressure on a brake pedal and transferring that pressure by linkages to pads that applied the pressure to a drum or rotor attached to the axle. That friction slows or stops the vehicle. To increase the pressure from the braking system on the axles to control heavier vehicles or to reduce the strain on the driver, hydraulics have replaced mechanical linkages. Now when the brake pedal is depressed, a hydraulic cylinder forces fluid through brake lines that connect the main cylinder to hydraulic cylinders at each wheel. The fluid then forces the pads onto the rotors, which slows or stops the vehicle. To further increase the pressure on the pads, pumps can be added to increase the hydraulic pressure. With large vehicles, such as fire apparatus, even this type of braking may not provide the level of safe braking that is needed. Large vehicles use air brakes to slow or stop the vehicle. In these brakes, air is used either to keep the brake pads off the cylinder or to apply the pressure. These work in a similar way to the others described, but are designed to apply brakes any time air pressure is lost or suddenly reduced. Once again, brake systems are being computerized and now have features that prevent brakes from locking up and causing the vehicle to skid.

The Steering Assembly

The steering wheel is attached to the tip of the steering column. In older vehicles, the bottom of the column was directly attached to the wheels by a series of gears and levers, so that if the steering wheel was turned to the right, the vehicle turned right, and vice versa. Today, the steering system of a vehicle employs hydraulics either to assist in the movement of the wheels or to actually move them. Modern steering systems allow the vehicle operator to turn the vehicle with much greater ease than older steering systems.

The Exhaust System

As each cylinder fires, the combustion produces hot gases that expand in the confined space, forcing the piston down. For the engine to continue to function, it must exchange the burnt gases for fresh air and then, at the right moment, fuel. This exchange of combustion gases for fresh air is the job of the exhaust system. From an exhaust valve or from a series of ports, the burnt gases are drawn into a device called an exhaust manifold that gathers the gases from all the cylinders. This is connected to welded piping that passes the exhaust gases through a scrubbing device to remove harmful gases, changing them to harmless exhaust gases. This device, frequently called a catalytic converter, discharges the scrubbed exhaust gases through a muffler, which is an acoustical chamber that reduces the engine noise.

Bicycles

A bicycle is not nearly as complex as an automobile. However, it too uses several mechanical devices.

• The chain drive. The pedals are connected to the drive gear. A chain is used to connect the drive gear to the gears on the rear wheel.
• The frame. Many welded joints are used to hold the frame together.
• The suspension system. Many newer bikes have suspension systems. The front wheel may use a hydraulic shock absorber. The rear wheel may use two springs in parallel to reduce shock to the rider.

Brushing Up on Related Topics

Some mechanical aptitude questions may require the use of math or science to determine the correct answer. This chapter cannot cover all the possible questions you might be asked on the firefighter exam, but here are suggestions for ways to increase your knowledge of math, science, and general mechanical aptitude.

Math

The required mathematical skills are primarily arithmetic (addition, subtraction, multiplication, and division) and geometry (angles and shapes). The arithmetic involved is almost always fairly simple. If you had trouble with arithmetic or geometry in your past schooling, you can brush up by reading the math chapter of this book. If you still want more help, pull out your old high school math book or check out a basic math book from the library.

Science

Science subjects such as physics, materials science, thermodynamics, and chemistry are confusing for some people, but they needn't be. Science is real, seen in everyday life. You see science in action dozens of times every day. A car is stopped by brakes, which use friction (physics). A magnet adheres to the refrigerator due to the properties of the magnet and carbon steel of which the door is made (materials science). A pot of water boils when you set it on the stove and turn on the burner (thermodynamics). A tomato plant grows through the chemical reaction of sunlight, water, and food (chemistry). This chapter has reviewed many of the scientific concepts that are involved in mechanical devices. Again, as with math, you may have science books from previous schooling that you can use to help you solidify your scientific knowledge. If not, the library is full of scientific resources.

General Mechanical Aptitude

Mechanical devices are such an integral part of everyday life that there are many real-life sources you can investigate to gain more knowledge of their design and use. A construction site is a great place to visit for a day to learn more about hand tools, cranes, pumps, and other devices. Ask the construction supervisor if you can take a tour.

Another alternative would be to visit an automotive repair shop. Internal combustion engines, lifts, levers, and hand tools are only a few of the types of mechanical devices you could see in use. Yet another possibility would be to visit a local manufacturer in your town. Examples include a foundry, a sheet metal fabricator, an automotive manufacturer, or a pump manufacturer. Look in the phone book under "manufacturing" for possibilities.

Sample Mechanical Aptitude Questions

1. Which of the following tools is used to smooth or level a piece of wood?
   1. a wrench
   2. a screwdriver
   3. a plane
   4. a hammer
2. A compass is used for what purpose?
   1. to measure angles
   2. to tighten and loosen nuts and bolts
   3. to drive and remove nails
   4. to draw circles of various sizes
3. Which of the following is NOT a hand tool?
   1. a winch
   2. a level
   3. a compass
   4. a chisel
4. Vice grips are a type of
   1. ax.
   2. wrench.
   3. ladder.
   4. mechanical jack.
5. How can gears be used to change the speed of a machine?
   1. How can gears be used to change the speed of a machine?
   2. use more gears
   3. use two gears of the same size
   4. use two gears of different sizes
   5. use two large gears
6. What is the main function of a pulley?
   1. to increase the strength of a construction crane
   2. to override the power of an electric motor
   3. to add energy to a system
   4. to change the direction of a pulling force
7. Steve has a lever whose pivot point is 3 feet from the 50-pound box he wants to lift. Steve is standing at the other end of the lever, 6 feet from the pivot point. How much force must he apply to lift the box?



1. 50 pounds
2. 25 pounds
3. 100 pounds
4. 6 pounds
8. Which of the following is NOT a mechanical process for fastening?
   1. welding
   2. buttoning
   3. bolting
   4. covalent bonding
9. When three identical springs are arranged in series and a pulling force of 10 pounds is applied, the total stretch is 9 inches. If these same three springs were arranged in parallel and the same 10-pound force were applied to the new arrangement, what would be the total distance of stretch?



1. 3 inches
2. 4.5 inches
3. 9 inches
4. 18 inches
10. What type of gauge uses units of rpm?
    1. a pressure gauge
    2. a tachometer
    3. a speedometer
    4. a thermometer
11. What type of outside energy source could be used to operate a pump?
    1. a battery
    2. an internal combustion engine
    3. an electric motor
    4. all of the above
12. What type of mechanical device is used to aid in cooling an internal combustion engine?
    1. a pump
    2. a lever
    3. a gauge
    4. a hammer
13. Of the following mechanical devices on an automobile, which one uses friction to accomplish its purpose?
    1. the steering system
    2. the exhaust system
    3. the braking system
    4. the internal combustion engine
14. The suspension system on a bicycle is likely to use which of the following mechanical devices?
    1. a chain
    2. a pulley
    3. a gear
    4. a spring
15. The tops and caps of your department's fire hydrants have a hexagonal stud extending about an inch from the base. Which of the following basic tools could you use to open the hydrant or remove the cap?
    1. pliers
    2. wrench
    3. screwdriver
    4. lever
16. What gauge could be used to test the amount of water streaming from a hydrant?
    1. tachometer
    2. pressure gauge
    3. speedometer
    4. flow meter

Answers

1. c. See the table under "Carpenter's Tools" earlier in this chapter for the functions of the items listed.
2. d. As defined under "Carpenter's Tools," a compass is used to draw circles.
3. a. A level, a compass, and a chisel are all carpenter's hand tools.
4. b. Vice grips are a kind of wrench.
5. c. Changing gears on a ten-speed bicycle is a good example of using different-sized gears to change speed.
6. d. Pulleys are used to change not the strength of a force but its direction.
7. b. Apply the distance formula, w × d₁ = f × d₂, to come up with the equation 50 × 3 = f × 6. Solve for the unknown f by multiplying 3 times 50 to get 150 and then dividing by 6 to get 25 pounds.
8. d. A covalent bond is a chemical bond. Welding, buttoning, and bolting are all mechanical fastening processes.
9. a. The total pulling force will be divided equally, with each spring experiencing one-third of the total force. Since the force is divided by 3, the amount of movement will be divided by 3 also. The original configuration stretched 9 inches, so the new arrangement will stretch only 3 inches.
10. b. A tachometer measures rotation in units of revolutions per minute or rpm.
11. d. Any of the energy sources listed could be used to operate a pump.
12. a. As discussed in the section "Internal Combustion Engines" earlier in this chapter, a pump is used to help cool an ICE.
13. c. The braking system uses friction to slow or stop the rotation of the wheels.
14. d. Springs are commonly used in suspension systems.
15. b. A wrench is used to turn a bolt-like head. Although pliers could be used, they would tend to slip. Both a lever and a screwdriver would be useless in this instance.
16. d. Flow meters measure the volume of flow within a piping system or flowing from a piping system. A pressure gauge would show you the pressure of the water, but you are not interested in that. You need to measure flow, the volume (amount of water), not the pressure (force of water). Tachometers and speedometers measure machinery speed, not water speed or volume.

How to Answer Mechanical Aptitude Questions

• Read each problem carefully. Questions may contain words such as not, all, or mostly, which can be tricky unless you pay attention.
• Read the entire question once or even a few times before trying to pick an answer. Decide exactly what the question is asking. Take notes and draw pictures on scratch paper. That way you won't waste time by going in the wrong direction.
• Some questions will require the use of math (typically addition, subtraction, multiplication, and division) and science. In these situations, think about what you have learned previously in school.
• Use your common sense. Some mechanical devices can seem intimidating at first but are really a combination of a few simple items. Try to break complicated questions down into smaller, manageable pieces.
• Answer the questions that are easiest for you first. You do not have to go in order from start to finish. Read each question and, if you are not sure what to do, move on to the next question. You can go back to harder questions if you have time at the end.
• Many mechanical devices are commonly used in everyday life. You do not have to be a mechanic or an engineer to use these devices. If something seems unfamiliar, try to think of items around your house that might be similar.
• Don't be intimidated by unfamiliar terms. In most instances, there are clues in the question that will point you toward the correct answer, and some of the answers can be ruled out by common sense.