Pulleys, Gears, and Levers Flashcards

A firefighter is using a Halligan tool to pry open a door, with the door jamb acting as the fulcrum. To generate the maximum prying force on the door (the load), where should the tool be positioned relative to the jamb?

Answer: So the distance between the jamb and the door edge is as short as possible.

This is an application of a Class 1 lever. To maximize mechanical advantage, the distance from the fulcrum (door jamb) to the load (the part of the tool prying the door) must be minimized, while the distance from the fulcrum to the effort (the firefighter's hands) is maximized. A shorter load arm requires less effort to achieve the same output force.

A small gear with 15 teeth is driving a larger gear with 60 teeth. Which of the following correctly describes the relationship between the two gears?

Answer: The large gear will rotate with four times the torque of the small gear.

The gear ratio is calculated by dividing the number of teeth on the driven (large) gear by the number of teeth on the driver (small) gear (60/15 = 4). This 4:1 ratio means the output speed is reduced by a factor of 4, and the output torque is multiplied by a factor of 4 (ignoring friction).

A rescue team is using a rope and pulley system to lift a 600-pound piece of equipment. Ignoring friction, which of the following systems would allow a rescuer to lift the load by pulling with approximately 150 pounds of force?

Answer: A system with a 4:1 mechanical advantage.

Mechanical advantage is the ratio of the load force to the effort force. To lift a 600-pound load with 150 pounds of effort, a mechanical advantage of 4:1 is needed (600 / 150 = 4). The number of supporting rope segments determines the mechanical advantage.

The large turntable gear on an aerial apparatus is rotated by a small pinion gear connected to a hydraulic motor. What is the primary mechanical principle behind this design?

Answer: It allows the small motor to generate the immense torque required to rotate the heavy ladder assembly.

This gear setup creates a large gear reduction (a high gear ratio). This reduction in speed from the small pinion gear to the large turntable gear results in a significant multiplication of torque, allowing a relatively small motor to control the massive weight and inertia of the aerial ladder.

A firefighter uses a wheelbarrow to move heavy debris away from a building. The wheel's axle is the fulcrum, the debris is the load, and the firefighter lifts the handles to provide the effort. According to the principles of simple machines, what class of lever is a wheelbarrow?

Answer: Class 2 Lever

A Class 2 lever is defined by having the load located between the fulcrum and the effort. In the case of a wheelbarrow, the fulcrum is the wheel axle, the load is the debris in the basin, and the effort is applied by the firefighter lifting the handles.

A pulley system is configured so that there are 5 rope segments directly supporting the load. If a firefighter needs to lift a 500-pound patient, what is the ideal force required to lift the load, assuming the system is frictionless?

Answer: 100 pounds

The ideal mechanical advantage (IMA) of a pulley system is equal to the number of rope segments supporting the load. In this case, the IMA is 5. The force required is the total load divided by the mechanical advantage (500 pounds / 5 = 100 pounds).