Differences Between Movable and Fixed Pulley with Examples
A movable pulley is a simple mechanical device that helps make lifting heavy objects much easier by reducing the amount of force required. This is achieved by allowing the pulley itself to move along with the load, letting you use your effort more efficiently. For JEE aspirants, understanding the mechanics, force distribution, and calculation formulas of such pulleys is key for accurate problem-solving in Physics questions and real-life application analysis.
Movable Pulley – Definition and Working Principle
A movable pulley is a type of pulley in which the wheel is attached directly to the load and both move together. When a force is applied to lift the load, the pulley moves upwards, effectively sharing the weight between the sections of the rope. The essential working principle is based on force redistribution, giving a mechanical advantage that makes it possible to lift heavier weights with less effort.
According to the principle of simple machines, a movable pulley reduces the input force needed by increasing the distance over which the force must act. The ideal setup assumes negligible friction and a massless, inextensible rope.
Fixed vs Movable Pulley: Key Differences
| Aspect | Fixed Pulley | Movable Pulley |
|---|---|---|
| Wheel Position | Attached to a fixed support | Moves with the load |
| Mechanical Advantage | 1 | 2 (ideal) |
| Force Direction Change | Yes | No (doesn't change) |
| Effort Reduction | No | Yes |
| Use Case | Wells, flagpoles | Lifting cargo, construction |
The fixed pulley alters the direction of force but doesn't reduce its magnitude, whereas the movable pulley actually decreases the force required, making it more efficient for lifting heavy loads. Compare more about fixed pulley at Single Fixed Pulley.
Movable Pulley Diagram, Setup, and Force Distribution
A typical movable pulley system for JEE consists of a rope passing through a movable wheel (attached to the mass), with one rope end fixed to a support and the other used for applying effort. Both rope segments support the load, distributing the tension and reducing the force enough to make lifting practical. This configuration is foundational for exam diagram practice and concept retention.
Tip for exams: Always label forces and directions, and mention when the pulley and rope are massless and frictionless for maximum scoring in diagram-based questions.
Mechanical Advantage of a Movable Pulley – Formula and Example
The mechanical advantage (MA) of a movable pulley system is the ratio of load lifted (W) to the effort applied (P):
MA = W / P
In an ideal single movable pulley with negligible friction and a massless rope, mechanical advantage is 2. This means the effort needed is half the weight of the load.
- Let load W = 200 N
- Mechanical Advantage (ideal) MA = 2
- Effort required: P = W / 2 = 100 N
Therefore, you only need 100 N force to lift a 200 N weight using an ideal movable pulley. For more formula practice, visit Single Movable Pulley.
Block and Tackle: Compound Movable Pulley Systems
A block and tackle system combines movable and fixed pulleys to further increase the mechanical advantage. Multiple pulley wheels, arranged in blocks, enable even greater effort reduction for heavy-duty lifting as used in cranes or cargo loading.
Mechanical advantage in a block and tackle equals the total number of supporting rope segments. Study more at Block and Tackle System and explore its exam-centric calculations.
Movable Pulley Examples: Real-Life and Human Body Applications
- Construction cranes use compound pulleys to lift materials efficiently
- Elevators and cargo lifts (with counterweight) leverage movable pulleys
- Zip-lines use pulley wheels to reduce friction and ease movement
- Window blinds and certain gym equipment feature movable pulley setups
- In the human body, the patella (knee cap) acts as a movable pulley for improving leg movement efficiency
The daily use of these systems showcases the practical value of pulleys beyond theoretical problems. See more collective uses via Applications of Simple Machines.
Advantages and Disadvantages of Movable Pulley Systems
| Advantages | Disadvantages |
|---|---|
| Reduces required effort for lifting heavy loads | Pulley and rope move together, sometimes making the setup unstable |
| Mechanical advantage is usually 2 or more | Does not change direction of applied force |
| Easy to combine with other pulleys for more efficiency | Prone to more practical friction losses |
Common Pitfalls and Tips for JEE Pulley Questions
- Do not assume MA = 2 when friction or pulley/rope mass is involved
- Always identify all rope segments supporting the load before applying formulas
- Label diagrams with proper force directions for clarity and scoring
- When solving numericals, check if it's a simple or compound (block and tackle) system
- Practice tension calculations and direction conventions to avoid careless mistakes
Mastering the movable pulley concept will help you solve typical JEE mechanics problems and apply core laws such as Newton’s laws of motion. A careful approach to diagrams, force analysis, and formula usage ensures accuracy in both numericals and explanation-based questions. For more, explore Work, Energy and Power and Friction for linked Physics ideas. Vedantu supports your JEE journey by offering up-to-date resources reviewed by experienced educators.
FAQs on Movable Pulley – Concept, Diagram, and Uses
1. What is a movable pulley?
A movable pulley is a type of simple machine where the pulley wheel moves along with the load, making it easier to lift heavy objects. In this system:
- The pulley is attached to the load, not a fixed surface.
- Pulling the rope lifts both the pulley and the object together.
- It offers mechanical advantage, usually allowing you to use half the force needed compared to lifting directly.
2. What is the difference between a fixed and a movable pulley?
The primary difference between a fixed pulley and a movable pulley is in their setup and function:
- Fixed Pulley: The wheel is firmly attached to a support. It only changes the direction of force but does not provide mechanical advantage.
- Movable Pulley: The wheel moves with the load. It reduces the force required to lift but does not change the force direction.
3. What are the advantages of using a movable pulley?
A movable pulley provides several advantages in mechanical systems and daily life:
- Reduces the effort required to lift heavy loads by providing mechanical advantage.
- Allows one person to lift weights that would otherwise need two or more people.
- Can be combined with other pulleys to increase force multiplication (block and tackle).
- Commonly used in cranes, hoists, and elevators.
4. What is the mechanical advantage formula for a movable pulley?
The mechanical advantage (MA) of a single movable pulley is 2, meaning the effort needed is half the load's weight. The formula is:
- MA = Load / Effort = 2 (for an ideal, frictionless single movable pulley)
- With multiple pulleys, MA = number of rope segments supporting the load.
5. Can you give examples of movable pulleys in daily life?
Movable pulleys are found in various practical and real-life setups:
- Construction cranes and hoists
- Elevator pulley systems
- Gym weight machines
- Sailing and ship rigging
- Block and tackle systems for heavy lifting
6. What are the disadvantages of movable pulleys?
Moveable pulleys also have some limitations:
- They do not change the direction of effort force, requiring vertical pulling in most cases.
- Due to friction and weight of the pulley, actual mechanical advantage is often less than 2.
- Require support above the load to operate effectively.
7. How does a block and tackle system work using movable pulleys?
Block and tackle systems combine fixed and movable pulleys to maximize mechanical advantage. How they work:
- Multiple pulleys are grouped together (blocks), with some fixed and some movable.
- The load is divided among several rope segments, reducing the required effort.
- Mechanical advantage equals the number of rope segments supporting the load.
8. What are some examples of moveable pulleys in the human body?
Movable pulley analogies in the human body make concepts more relatable:
- The patella (kneecap) acts like a movable pulley, redirecting and amplifying the force from thigh muscles to the lower leg during movement.
- Tendons around joints can create a pulley system, reducing the effort needed for movement.
9. Why is mechanical advantage important in competitive exams like JEE?
Mechanical advantage shows how much a machine multiplies input force, making it vital for:
- Solving physics numericals on simple machines and pulley systems
- Explaining force, work, and efficiency in exam questions
- Ensuring quick, accurate problem-solving in JEE, NEET, and board exams
10. How do diagrams improve your answers in board exams for pulley questions?
Well-drawn pulley diagrams make your answers clearer and boost marks by:
- Helping examiners understand your solution steps
- Making force direction and setup easy to explain
- Demonstrating conceptual clarity for full step marking
