Do Pulley Systems Make Things Lighter?

This year in 6th class for the RDS Science Blast we decided to investigate pulley systems. First we made a single fixed pulley system but discovered that it made no difference to the weight. Then we made a multiple fixed pulley system. We calculated that there was a mechanical advantage of 1.8 with this method. Next we made a multiple pulley system using a movable pulley and a fixed pulley. This had the biggest mechanical advantage 3. Finally we wanted make a structure used in everyday life so we decided on a crane. We made the crane out of modelling wood and used 3 fixed pulleys and 1 moveable pulley. We also made a handle out of an old pencil which attaches to the pulleys and makes the crane work when you wind it. We really enjoyed doing this project.