Table of Contents Simple Machines


3. Have students work in groups of two or three per boat to rig a boat and identify the pulley types on board, the load, and the direction of applied force.


4. Using a blank sheet of paper have students sketch the rig they are using, labeling each pulley system on board.


5. When students have completed rigging their boats and identified the pulley types on the boats, students can either de-rig or launch.


Part IV: 1:1 vs 4:1 Purchase On the Water - 60 minutes


Note: This activity can be modified to be done on land, as seen on left, by Edison Sailing Center.


1. Ask students to identify the load on the main sheet block. Ask students if this load (pressure on the sail) ever changes? How and when does it change? Explain to students that the load in this case is the amount of pressure on the sail caused by the wind and the point of sail. Sailors reduce the amount of work needed in windy conditions by modifying the purchase system which is a compound pulley.


2. While sailing ask students to tack or gybe by grabbing the top of the purchase and changing the sail without using the purchase. Then, ask them to tack using the purchase and ask the about the difference.


3. Have a race with 1:1 purchase boats vs 4:1 purchase or more. Does one sail faster than the other? Does one sailor need to exhort more effort (work) than the other? Which point of sail requires the most work from the skipper? Why?


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