In physics, ideal pulley and spring systems are simplified models used to solve problems involving force, tension, and motion without considering friction or energy loss.
1. Ideal Pulley System
Definition
An ideal pulley is:
- Massless
- Frictionless
- Uses a light, inextensible string
Key Principles
- Tension is the same throughout the string
- Pulley only changes the direction of force, not its magnitude (in simple pulley)
- In multiple pulleys, force gets distributed
Example
If a mass is hanging on a pulley:
- Tension (T) = Weight (mg) in equilibrium
- In complex systems, apply Newton’s laws to each mass
2. Ideal Spring System
Definition
An ideal spring follows Hooke’s Law:
F = kx
Where:
- F = restoring force
- k = spring constant
- x = displacement
Key Principles
- Force is directly proportional to extension or compression
- Always acts in the opposite direction of displacement
- No energy loss (perfectly elastic)
Oscillation
When disturbed, the system performs Simple Harmonic Motion (SHM):
- Motion is periodic
- Restoring force brings it back to equilibrium
Combined Systems (Pulley + Spring)
- Use force balance equations
- Apply Newton’s Second Law (F = ma)
- Consider tension and spring force together
Summary
- Ideal pulley → simplifies force distribution and direction
- Ideal spring → follows Hooke’s law and shows SHM
- Both systems help solve mechanics problems efficiently