Biomechanics and Fluid Dynamics Notes 3/27/25

Definition: The lever system consists of an axis of rotation and arms (or levers) attached to it.
Application: The principles of lever systems apply to understanding muscle mechanics and joint function.
- Example: Analyzing the elbow joint and biceps curl as a lever system where:
- Axis: Elbow joint
- Resistance: Weight of the dumbbell being lifted
Equilibrium: To balance a lever, an upward force must counteract the downward weight, requiring knowledge of torque rather than just matching forces.
Torque: Torque is critical in understanding how muscles work to lift loads at various angles.

Newton's Third Law: For every action, there is an equal and opposite reaction.
- Example: A sprinter pushing against starting blocks experiences equal force pushing back.
Force and Acceleration Calculation:
- Formula: a = F/m
- Example Problem: If net force (F) is 3 N and mass (m) is 3 kg, then acceleration (a) = 1 m/s².

Definition of Fluid: Fluids include gases (like air) and liquids (like water).
Effects of Fluid on Movement: When swimming or running, a drag force acts against movement.
- Drag Force: Created by fluid (water/air) resistance opposing body motion.
Comparison of Drag Forces: Water creates more drag resistance than air.
Types of Drag Forces:
- Profile Drag: Caused by shape and size of the object.
- Surface Drag: Related to the roughness of the object's surface.

Key Concept: Drag force increases with the square of speed.
- Example: Doubling speed (from 10 mph to 20 mph) results in four times greater drag.
Importance in Sports: Understanding drag can improve performance in activities like cycling and swimming.

Drafting: A technique used to reduce drag by positioning oneself behind another athlete.
- Benefits: Can reduce energy expenditure by as much as 6% when within 3 feet of the leader.
Strategic Application: Used in marathon running and cycling to conserve energy.

Definition: The phenomenon where a spinning object generates a pressure differential, causing it to curve in its flight path.
- Example: Soccer player Roberto Carlos’s curved kicks demonstrate this effect.
Applications: Found in various sports, including baseball and tennis, influencing the trajectory of balls.

Static vs. Dynamic Equilibrium:
- Static Equilibrium: No movement or change in direction.
- Dynamic Equilibrium: All forces are balanced while in motion (e.g., riding a bike at constant speed).
Factors of Stability:
- Base of Support: Widening stance increases stability.
- Line of Gravity: Must fall within the base of support to maintain balance.
Strategies to Increase Stability:
- Increasing base size
- Lowering center of gravity

Kinematics: Study of motion without considering forces (includes variables such as time, displacement, velocity, acceleration).
Kinetics: Focuses on forces that cause motion (internal and external forces acting on bodies).
Importance of Both Analyses: Understanding both perspectives is crucial for biomechanics and human motion studies.

Levels of Modeling:
- Particle Model: Simplest representation, treating the body as a point.
- Stick Figure Model: Represents the body by segments connected like sticks, useful for visualizing motions in 2D.