Students will investigate how simple machines help move large loads on a ship.
How can you lower or raise something heavy with just the power of your arms pulling on a rope? Brainstorm real-world situations where large, heavy loads must be lifted, moved and lowered with a minimum of energy (fuel) expended. Explain that in these Activities, students will construct simple machines to move loads.
Do you gain mechanical advantage by using more than 3 pulleys to compound the force?
It's rarely worth more than three pulleys to compound the force because friction starts to reduce the mechanical advantage. In addition, you can see from Figure 3 that the rope suspending the upper pulley block needs to be stronger and stronger to hold the weight of the object to be lifted plus the weight of the weights and pulley blocks.
Uses of Rigging on Ships
One of the most important early applications of block and tackle rigging was for raising, lowering, and controlling sails. Engine powered fishing and research ships depend on these mechanisms too. Instruments are often lowered into the ocean on the ends of long cables. The pressures of the sea are very strong so the machinery has to be rugged.
Read Deane Rink's on-line, hair-raising account of his cargo-handling "experience" involving the Duke's winches. After viewing the videos, write a journal entry describing a day aboard the Duke. Include information about the rigging, cargo and instrument-handling equipment. Place copy in Logbook.
Using a world map, plot a course that would take a ship such as the R/V Polar Duke to all the major oceans of the world. Using print or on-line sources, research basic information about these oceans, including salinity, major ocean currents and upwellings, bottom canyons, storm belts and other factors that would be critical to successful circumnavigation.
Use data from on-line or the videos to calculate the Duke's average speed. How long would it take to travel to each place, and complete the entire journey?