Lecture Notes: Stability, Equilibrium, and Levers

Important Dates

• Worksheet 5 Due: This Friday
• Lab Week: Project work week with no in-person meetings

Topics Covered

• Review of previous lecture
• Stability and Equilibrium
• Anatomical Levers
• Mechanical Advantage and Disadvantage

Stability and Equilibrium

Key Concepts

• Stability: Ability to maintain static equilibrium (sum of all torques equals zero).
• Factors Influencing Stability:
  1. Mass: More mass, more stability.
  2. Friction: Higher friction increases stability.
  3. Base of Support: Wider base increases stability.
  4. Center of Mass Location: Lower center of mass increases stability.

Increasing Stability

• Widen stance to increase base of support.
• Keep belly button within base of support for balance.
• Lower the body by bending knees to lower the center of mass.

Examples of Stability

• Kobe playing defense: Increased base of support, lower center of mass, shoes with high friction.
• Grappling Sports (e.g., Wrestling): Sprawl technique to lower center of mass and widen base of support.

Lever Systems

Components of a Lever

• Rigid Bar rotates around an Axis of Rotation.
• Force applied to move a Resistance.

Anatomical Levers

• Bones: Act as rigid bars.
• Joints: Serve as axis of rotation.
• Muscle Force: Causes rotation.
• Resistive Forces: External objects or antagonist muscles.

Types of Levers

1. First Class Lever: Axis in the middle.
   • Example: See-saw, Atlanto-occipital joint.
2. Second Class Lever: Resistive force in the middle.
   • Example: Plantar flexion of the foot, push-up.
3. Third Class Lever: Muscle force in the middle.
   • Example: Elbow joint, knee joint.

ARM Mnemonic for Levers

• A First Class: Axis in the middle
• R Second Class: Resistance in the middle
• M Third Class: Muscle in the middle

Mechanical Advantage and Disadvantage

Definitions

• Mechanical Advantage (>1): Less muscle force needed, less range of motion.
• Mechanical Disadvantage (<1): More muscle force needed, more range of motion.

Lever Systems Overview

• Second Class Levers: Always mechanical advantage.
• Third Class Levers: Always mechanical disadvantage.

Example Calculations

• Push-up (Second Class Lever):
  • Longer moment arm for muscle force, thus less muscle force needed.
• Bicep Curl (Third Class Lever):
  • Shorter moment arm for muscle force, more muscle force needed.

Influence of Height on Lever Systems

• Taller Individuals: Longer external lever arms increase torque requirement.
• Shorter Individuals: Shorter lever arms, easier torque management.

Summary Questions

• What determines stability and how to manipulate these factors?
• What are the arrangements of the three types of levers?
• Examples of mechanical advantage and disadvantage.

Next Steps

• Prepare for review game on Cahoot.
• Review lecture slides available in PDFs.