Compare two ways to reduce the force needed to lift the same load.
Select a page to enlarge it.
A fixed pulley mainly changes the direction of the pull. A moving pulley can share the moving load between supporting rope segments. In an ideal continuous rope over frictionless pulleys, the tension is the same throughout.
If four rope segments support an ideal moving block, the input force is one quarter of the total supported weight. Raising the block 0.5 m requires pulling about 2 m of rope. A smaller force comes with more input distance.
For a frictionless ramp at steady speed, input work equals the increase in gravitational potential energy. Ideal mechanical advantage is ramp length divided by vertical height. The ramp length is measured along the slope, not horizontally.
Keep load and lifting height fixed. Measure force with a spring scale, input travel and output rise. Compare the complete lift rather than one instant. A load that speeds up adds another energy change to consider.
Choose a pulley arrangement. Move the load with the mouse and press to reveal the spring balance. Change the load and moving-pulley weight, then compare the pull with the number of supporting strands.
This app caps the spring scale at 10 N and can adjust out-of-range inputs. Read the displayed values after each change. It is an ideal pulley model, not safe lifting guidance.
SmarterEveryDay · Mechanism in action
Count the strands supporting the moving load. Compare a direction change with a force advantage. Watch the explanation rather than copying the lifting setup.
An ideal ramp is 3 m long and rises 0.75 m. What is its distance ratio?
3 ÷ 0.75 = 4. For a steady frictionless lift, the force advantage is also 4.
Compare a fixed pulley with a moving-pulley system. Explain why counting the wheels alone can give the wrong answer.
Apply it to the design challenge →Read further: OpenStax · Simple Machines →
