Which is more labor-saving, fixed pulley or movable pulley and why?
3 Answers
Using a movable pulley can save half the force (provided the gravity of the movable pulley can be ignored), while using a fixed pulley definitely does not save force. When the gravity of the movable pulley is less than the gravity of the object: When the gravity of the movable pulley is less than the gravity of the object, using the movable pulley saves force. If the gravity of the movable pulley is greater than that of the object, it certainly does not save force. People would not use a very heavy movable pulley to lift a feather. When using a movable pulley: When using a movable pulley, lifting the object also requires lifting the movable pulley. If the movable pulley is heavy, the additional work done is relatively more. When using a fixed pulley to lift an object, the fixed pulley does not move with the object, so no additional work is done on the fixed pulley (only additional work is done to overcome friction). Therefore, generally speaking, using a fixed pulley has higher mechanical efficiency.
Back when I was young and working at the auto shop, I often handled heavy car parts like engines or tires. During that time, I experimented with different types of pulleys, and the movable pulley was noticeably more labor-saving. The reason is that a movable pulley can share the load. For example, if you're lifting a heavy object, using a movable pulley means the force I apply to the rope is only about half the actual weight, making it feel much easier. A fixed pulley only changes the direction of the force, like converting a downward pull into an upward lift, but the amount of force required remains the same—there's no labor-saving effect. This is quite common in car repairs. For instance, when working on the suspension system, choosing a movable pulley can save a lot of effort and reduce fatigue. From experience, saving effort isn't just about being lazy—it's also a matter of safety and efficiency. If you use a fixed pulley, applying too much force could even strain your muscles, which isn't worth it. The design of the movable pulley naturally distributes the load, making it highly practical.
As someone who frequently tinkers with tools, I understand the difference between pulleys quite simply: a movable pulley saves more effort. Why? Because it distributes the load—imagine pulling a rope while the pulley shares the weight, reducing the applied force to roughly half of the load. A fixed pulley, on the other hand, only changes the direction of the force, like pulling from below to above, without altering the amount of effort required. In the automotive field, for example, when changing tires, using a movable pulley mechanism makes the job easier—you don’t need as much strength to move heavy objects. This principle stems from basic physics, but I prefer not to overcomplicate it—the core idea is that sharing the load lightens the effort. In daily work, this saves me time and energy, avoiding issues caused by brute force. When choosing a pulley, the movable one is undoubtedly the go-to for immediate results.
