### Brushing Up on Related Topics

Some mechanical comprehension 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 ASVAB, but here are suggestions for ways to increase your knowledge of math and science and your general mechanical comprehension.

### Math

The math you may need for Mechanical Comprehension questions are simple arithmetic (addition, subtraction, multiplication, and division) and geometry (angles and shapes). 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 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, everyday life. You see science in action dozens of times every day. A car is stopped by brakes, which use friction—that's physics. A magnet adheres to the refrigerator door due to the properties of the magnet and carbon steel of which the door is made—that's materials science. A pot of water boils when you set it on the stove and turn on the burner—that's thermodynamics. A cake rises through the release of carbon dioxide from the baking powder or baking soda reacting with heat or an acid—that's 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 Comprehension

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 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 yellow pages under "manufacturing" for possibilities.

### Mechanical Comprehension Review Practice Questions

Try the Mechanical Comprehension questions below. Answers and explanations are at the end of the chapter.

- In a set of different sized pulleys, which will turn the fastest?
- the largest pulley
- they will all turn at the same speed, given the same belt speed
- the smallest pulley
- it depends on the speed of the machine

- 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?
- 50 pounds
- 25 pounds
- 100 pounds
- 6 pounds
- 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 are arranged in parallel and the same 10-pound force is applied to the new arrangement, what will be the total distance of stretch?
- 3 inches
- 4.5 inches
- 9 inches
- 18 inches
- Jan and Shirley begin traveling from the same point. Jan travels east at 30 mph for half an hour and Shirley travels west at 40 mph for one hour. How far apart are they at the end of their travels?
- 25 miles
- 55 miles
- 70 miles
- 120 miles

- If each of the following objects weighed the same, which would be easiest to drag?
- a wood object on a carpeted floor
- a wood object on a wood floor
- a glass object on a brick floor
- a glass object on a tiled floor

- Which of the following is one of the cycles of a four-stroke engine?
- compression
- decompression
- rotation
- ingestion

- Jar A contains a volume of 2 cubic feet of liquid and weighs 128 pounds. Jar B contains a volume of 3 cubic feet of liquid and weighs 216 pounds. Which liquid has a higher density?
- Jar A
- Jar B
- They have the same density.
- There is not enough information to answer the question.

- Which of the following best explains why wood floats on water?
- Wood is less dense than water.
- Water is less dense than wood.
- Water exerts more pressure than wood.
- Water is more buoyant than wood.

- Which of the following best describes the effect of heating a bar of steel?
- The bar will contract.
- The bar will expand.
- The bar will warp.
- The bar will remain unchanged.

- Given gear B, turning in the direction noted, what direction will gears A and C turn in?
- gear A will be clockwise and gear C will be clockwise
- gear A will be clockwise and gear C will be counterclockwise
- gear A will be counterclockwise and gear C will be counterclockwise
- the gears will seize up and not move

### Answers

**c.**The smaller pulley will turn faster than those larger than it. It has to turn faster in order to keep up.**b**. Apply the distance formula,*w*×*d*_{1}=*f*×*d*_{2}, 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.**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.**b.**Jan has traveled 15 miles to the east of the starting point, and Shirley has traveled 40 miles west of their starting point. Since east and west are in opposite directions, this puts a distance of 55 miles between them. If both had been traveling in the same direction at the given velocity and time, the distance separating them would have been only 25 miles.**d.**Glass and tile both have relatively low coefficients of friction.**a.**The four stages of a four-stroke engine are intake, compression, combustion, and exhaust.**b.**Divide the weight of each jar by its volume. The liquid in Jar A has density of 64 pounds per cubic foot, and the liquid in Jar B has a density of 72 pounds per cubic foot.**a.**Wood floats because it is less dense than the water it is floating on.**b.**Most materials expand when heated.**c.**The center gear is turning clockwise, and will cause the other two gears to turn in the opposite direction, or counterclockwise.

## 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.Use common sense.Some mechanical concepts can seem intimidating at first but are really a combination of a few more simple ideas. 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 concepts 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.

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