| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 2.62 |
| Score | 0% | 52% |
What's the last gear in a gear train called?
driven gear |
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idler gear |
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driver gear |
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output gear |
A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.
Which of the following is not true of a first-class lever?
increases distance |
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increases force |
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decreases distance |
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changes the direction of force |
A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.
| 1.38 ft. | |
| 5.5 ft. | |
| 1.83 ft. | |
| 11 ft. |
To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:
Rada = Rbdb
where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.Solving for db, our missing value, and plugging in our variables yields:
db = \( \frac{R_ad_a}{R_b} \) = \( \frac{55 lbs. \times 3 ft.}{30 lbs.} \) = \( \frac{165 ft⋅lb}{30 lbs.} \) = 5.5 ft.
A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?
tension is equal in all parts of the rope |
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near the car |
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in the middle |
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near the truck |
Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.
A wedge is most similar to what other type of simple machine?
second-class lever |
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third-class lever |
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inclined plane |
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first-class lever |
The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.