Definition: Two or more forces acting on the same line.
Directions: Can be same or opposite.
Same Direction: Forces add together.
Opposite Direction: Forces cancel each other out.
Ideal Scenario: Rarely occurs in reality; forces usually don't act on the same line.
Parallel Forces
Definition: Forces acting in the same plane but not on the same point.
Example: Three forces acting to reach a balance.
Concurrent Forces
Definition: Two or more forces acting on an object from different directions but at a common point.
Differences from Parallel Forces: Parallel forces act at different points, while concurrent forces act at a common point.
Example: Resultant force when two forces act on the same spot.
Importance in Clinical Practice
Tensile and Compression Forces
Application: Used to manipulate joints.
Tensile Force: Applied to separate joint spaces.
Compression Force: Used to keep tissues together.
Activity Design: Must ensure forces act on the same line for effective manipulation.
Shear Forces in Wheelchair Use
Problem: Weight pulls down, causing sliding due to wheelchair texture or angle.
Solution: Choose proper texture or change seating angle to prevent sliding.
Weak Shoulder Motion Example
Scenario: Weak shoulder motion with upper extremity weight (6 kg).
Solution: Add weight (e.g., 5 kg) to assist; patient only needs to generate minimal additional force.
Training: Modify intensity to gradually increase muscle strength.
Bucket Example: Adding weight requires generating more force to counteract combined weights.
Multiple Forces Acting on the Same Point
Simplification: Basic math equation can be used
Equation: a² + b² = c² for resultant force.
Application: Simplification helps understand resultant force in clinical settings.
Hand and Finger Movement
Natural Alignment: Center of finger movement lines deviates towards the radial side (scaphoid).
Splint Design: Must consider natural alignment for effective hand movement.
Resting Force Creation: Use elastic bands in strategic positions to ensure correct motion direction.
Summary
Understanding different types of forces and their applications is crucial in designing effective clinical interventions, particularly in activities involving joint manipulation, wheelchair seating, and muscle strength training.