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Pulleys Jenna Loux Alicia Ferrara Jess Myers Nicole Naula Use the Space Bar to Click through the Presentation Before Pulleys • In Ancient times, such as those in Egypt and the building of the Pyramids, to bare a heavy load brute manual labor was used to move each stone. • The slaves in ancient Egypt would pull heavy stones by placing it on boards and pulling ropes that were wrapped around the stone. • These stones had to be moved great distances and as the pyramid grew taller, it took more work to get it up the pyramid. This decreased the speed of the build as it went along. http://www.haitheory.com/ Things to think about… • It took about 2000 people to build a Pyramid • That makes approx. 45 groups of 45 • Which means 315 stones were moved a day • Which means 1,890 stones were moved a week • Which means it took approx. 1075 weeks to build the pyramid • 1075 weeks= 20.6 years • The Great Pyramid was built of approx. two million blocks of stone. • Each stone weighed approx 2800 kg (2.5 tons) • It took approx. 45 men to move a stone to its placement • Each day 45 men could move, on average, 7 stones • With a 12 hour work day, 6 days a week- one team could move 42 stones to place http://www.peter-thomson.co.uk/ancients/peoplepyramid.html Moving Stone Say you have a 100lb. Stone to move and you have to move it 100 feet To move it only using this rope your exerting the force to pull to entire weight of the stone. http://science.howstuffworks.com/transport/engines-equipment/pulley.htm Archimedes "Give me a lever long enough and a place to stand, and I will move the world." -Archimedes 230 BC http://www.hyperhistory.net/apwh/bios/b2archimedes_p1ab.htm Archimedes (287-212 BC) • Was a ancient Greek mathematician and scientist • When he was in his teens he was sent to Alexandria to study mathematics • Levers were used early to move heavy items but at the age of 27 Archimedes was able to explain why they worked • Explained to the king how pulleys can be implemented to move heavy objects. http://www.school-for-champions.com/biographies/archimedes.htm First Pulley Thoughts • If you just use one pulley to move the weight you are still exerting enough force to life the full 100lbs • You are still pulling 100 feet of rope to bring the item up 100 feet. http://science.howstuffworks.com/transport/engines-equipment/pulley.htm Two Pulley System • If you add a second pulley, two ropes are holding the item up instead of one • This splits the weight equally between the two pulleys • This means you only have to exert half the force needed to pull up the full amount of weight http://science.howstuffworks.com/transport/engines-equipment/pulley.htm Force-Distance Tradeoff When the force needed to pull something using a pulley is cut in half the distance of rope that needs to be pulled will double. http://science.howstuffworks.com/transport/engines-equipment/pulley.htm More Pulleys • The more pulleys you add the less amount of force you have to apply to pull the weight up • With each pulley used it cuts the force that must be used in half and the amount of rope needed doubles • So a 100lb stone being lifted 100ft with a three pulley system will need 400ft of rope but only 25% of the force is needed http://science.howstuffworks.com/transport/engines-equipment/pulley.htm Time and Energy Saver • Using this method it saves 25% of the energy needed to move a stone with each additional pulley used, where 1 pulley does not change the energy needed • With a 2 pulley system a pyramid could be built in 15 years, five years less than before. http://www.miniscience.com/projects/pulley/ Uses for Pulleys • • • • • • • • Elevators Lifting car engines Lifting marine cargo Cars Cranes Building Houses Tow Trucks Work-out machines