• Triangular shapes are rigid
• Rectangular shapes are not rigid
• Rectangular shapes can be strengthened (by adding a cross-brace) to make them rigid.
• Pushing (compression) forces and pulling (tension) forces act on shapes differently.
• The fulcrum, the effort, and the load can be arranged to increase force or to decrease movement.
• To raise a load with the least effort, the load is as close to the fulcrum as possible and the effort is as far from the fulcrum as possible.
• Belts turn pulleys in the same direction.
• Crossed belts make pulleys turn in the opposite direction.
• A small pulley and belt make a large pulley turn slowly
• A large pulley and belt make a small pulley turn faster.
• Meshed gears turn in opposite directions
• A large gear turns a small gear faster
• A small gear turns a large gear slowly.