Biomechanics Notes - Chapter 3 PDF

Chapter 3 **Biomechanics Notes** **Definition of Biomechanics** - Study of mechanics as it relates to the functional and anatomical analysis of biological systems, especially humans. - Applies physics, laws of motion, and forces to understand human movement. **Two Major Areas of Bio...

Chapter 3 **Biomechanics Notes** **Definition of Biomechanics** - Study of mechanics as it relates to the functional and anatomical analysis of biological systems, especially humans. - Applies physics, laws of motion, and forces to understand human movement. **Two Major Areas of Biomechanics** 1. **Kinematics**: Describes motion (movement details). - Time: How long it takes to move. - Displacement: How far you move. - Velocity: How fast you move. - Acceleration: How quickly movement changes. - Spatial factors: How motion occurs in space. 2. **Kinetics**: Studies forces causing motion. - Ground reaction forces (e.g., through force plates). **Biomechanics Labs and Motion Analysis** - **Motion Capture (Kinematics)**: - Infrared reflective markers track body segments in 3D space. - Captures displacement, velocity, and acceleration. - **Force Plates (Kinetics)**: - Measure ground reaction forces in vertical and horizontal planes. **Machines in Biomechanics** - Provide **mechanical advantage**: - **Force advantage**: Small input force moves a larger resistance (e.g., car jack, breaker bar). - **Displacement advantage**: Small input movement causes a larger movement (e.g., casting a fishing rod). - **Musculoskeletal System as Machines**: - Bones, joints, and muscles work as simple machines to balance forces and alter their direction. **Types of Machines in the Human Body** 1. **Levers**: Most common. 2. **Wheel and Axles**: Alter force direction and provide leverage. 3. **Pulleys**: Alter force direction, e.g., tendons acting over joints. *Note*: The body does not have inclined planes, screws, or wedges. **Levers in the Human Body** - **Components**: 1. **Force**: Input applied (e.g., muscle contraction). 2. **Axis (Fulcrum)**: Pivot point for rotation (e.g., joint). 3. **Resistance**: Load or weight moved by the force. - **Classes of Levers**: 4. **First-Class Lever**: - Axis is between force and resistance. - Example: Seesaw, neck extension. 5. **Second-Class Lever**: - Resistance is between axis and force. - Example: Wheelbarrow, standing on toes. 6. **Third-Class Lever**: - Force is between axis and resistance. - Example: Bicep curl, most body movements. **Action Steps for Study** - Draw and label diagrams for first-, second-, and third-class levers. - Familiarize yourself with examples of levers in the body. - Focus on the relationship between force, axis, and resistance for each class. **Levers** **Key Concepts** - A **lever** consists of a **force**, **axis (fulcrum)**, and **resistance** arranged in different orders, defining the class of lever. - **Mechanical advantage (MA)** = Length of force arm ÷ Length of resistance arm. - Determines how much force is required to balance or move a resistance. **Torque** - **Torque** = Force × Distance from the axis (moment arm). - Torque causes rotational movement around the axis. **Classes of Levers** 1. **First-Class Levers** - Axis is between force and resistance (e.g., seesaw, scissors). - Purposes: Balance, speed, or range of motion, depending on axis placement. - Example in the body: Head balanced on the neck (e.g., nodding). - Agonist and antagonist muscles stabilize the head. 2. **Second-Class Levers** - Resistance is between axis and force (e.g., wheelbarrow). - **Purpose**: Force advantage (move a large resistance with a smaller force). - Example in the body: Raising the body onto the toes. - Axis: Ball of the foot, Resistance: Body weight, Force: Calf muscles. - Rare in the human body. 3. **Third-Class Levers** - Force is between axis and resistance (e.g., rowing, shoveling). - **Purpose**: Speed and range of motion at the expense of force. - Example in the body: Bicep curl. - Axis: Elbow joint, Force: Biceps, Resistance: Weight in hand. - Most common lever type in the body. **Human Body Leverage System** - Built for **speed and range of motion**, not force. - Force arms in the body are typically short compared to resistance arms. - Muscles need significant strength to move long resistance arms (e.g., forearms). **Pulleys** **Key Concepts** - **Pulleys** redirect force and can increase mechanical advantage in multi-pulley systems. - **Mechanical Advantage** = Number of ropes supporting the load. - Single pulley: Changes direction of force, MA = 1. - Multiple pulleys: Increases MA (e.g., gym equipment with cables). **Pulley Example in the Body** - **Lateral malleolus** (ankle bone): Acts as a pulley for the **peroneus longus tendon**. - Function: Transmits force to the plantar aspect of the foot, allowing for eversion and plantarflexion. **1. Motion and Force** - Motion (movement) cannot occur without force. - **Types of Force:** - **Internal Force:** Muscle contractions (from the muscular system). - **External Force:** Interaction with external objects (e.g., being pushed, or objects colliding). **2. Types of Motion** - **Linear Motion:** Movement in a straight line. - **Angular Motion:** Rotational movement (e.g., a wheel turning). - Angular motion creates linear motion at the outer edges of the rotating object (e.g., a rock flung from a wheel). - **Relation Between Angular and Linear Motion:** - Angular motion at joints (e.g., hip/knee flexion and extension) generates linear motion (e.g., walking). - Larger radii (e.g., longer limbs or tools) produce greater linear velocity when angular motion occurs. **3. Examples of Angular and Linear Motion in Action** - Windmill blades: Longer blades produce higher linear velocity despite the same angular velocity. - Tools and equipment: - Long golf clubs = faster ball velocity. - Short golf clubs = slower ball velocity. - Vehicles: Larger wheels cover more ground per rotation than smaller wheels. **4. Newton\'s Laws of Motion** - Applicable to all linear and angular motion in biomechanics, sports, and physical activities. **Law 1: Law of Inertia** - **Definition:** - A body in motion stays in motion, and a body at rest stays at rest unless acted upon by an external force. - **Applications:** - Muscles generate force to overcome inertia (e.g., starting/stopping motion, accelerating, decelerating). - Examples: - Skier maintains trajectory until a force acts (e.g., wind resistance, friction). - Bowling ball rolls steadily on a slick floor unless force is applied. - **Mass and Inertia:** - Greater mass = greater inertia (more force required to change motion). - **Practical Examples:** - Sprinter overcoming resting inertia in starting blocks. - Slowing down a fast-moving object (e.g., stopping a ball). **Law 2: Momentum and Impulse** - **Momentum (p):** Quantity of motion = Mass × Velocity. - Greater momentum = Greater resistance to changes in motion. - Example: A larger, faster-moving object has more momentum than a smaller, slower one. - **Impulse:** - Impulse = Force × Time. - A force applied over time changes momentum. - **Applications of Impulse:** - Kicking a ball: The foot delivers an impulse, changing the ball\'s momentum. - Catching a ball: Extending arms slows down the ball gradually, reducing the force felt. - Helmets: Padding increases time of impact, reducing impulse on the skull. **Other Related Concepts:** - Reducing impulse to minimize impact: - Catching techniques (e.g., bringing arms inward when catching). - Protective equipment (e.g., helmet padding, Guardian caps for NFL players). **Summary of Key Biomechanics Applications** - **Angular Motion → Linear Motion Coupling:** - Seen in walking, running, tool usage, and equipment design. - **Newton's Laws of Motion:** - Inertia and momentum explain motion dynamics and resistance. - Impulse describes how forces modify motion. - **Practical Insights:** - Leverage force and radius for better efficiency in sports and physical tasks. - Use biomechanics principles to improve safety and reduce injury. **Newton's Second and Third Laws, Acceleration, Friction Notes** **Newton's Second Law: The Law of Acceleration** 1. **Definition of Acceleration**: - Acceleration is the change in velocity (not speed). - Positive or negative (e.g., braking = acceleration in the opposite direction of velocity). 2. **Key Concepts**: - **Equation**: Acceleration a=Fma = \\frac{F}{m}a=mF​ (Force divided by Mass). - Acceleration is: - **Directly proportional** to the force applied. - **Inversely proportional** to the mass of the object. - Larger mass requires more force to accelerate; smaller mass is easier to accelerate. 3. **Applications**: - Movement is rarely constant speed; it typically involves acceleration. - Example: A strong person pushing a heavy truck applies significant force, but the large mass limits acceleration. 4. **Muscular Force**: - High force is required to accelerate larger masses (e.g., big person reaching high speeds needs substantial effort). **Newton's Third Law: The Law of Reaction** 1. **Definition**: - For every action, there is an equal and opposite reaction. 2. **Applications**: - **Ground Reaction Force**: - Key to movement (walking, running, jumping). - The force exerted by the ground in response to the force applied by your feet. - Hard surfaces provide higher ground reaction force; soft surfaces (e.g., sand) provide less resistance. - Example: Walking on sand is harder because lower ground reaction force reduces propulsion. **Friction in Motion** 1. **Definition**: - Friction is the resistance between two surfaces in contact. 2. **Types of Friction**: - **Static Friction**: - Resistance between objects not yet moving. - Always **greater than kinetic friction**. - **Kinetic Friction**: - Resistance during motion between surfaces. 3. **Examples**: - **Static Friction**: - Pushing a sled: High initial force needed to start moving (overcoming static friction). - **Kinetic Friction**: - Once the sled moves, less force is required to keep it in motion. 4. **Factors Affecting Friction**: - **Surface Texture**: - Rougher surfaces = more friction. - Smoother surfaces (e.g., turf) = less friction. - **Normal Force**: - Increasing perpendicular force (e.g., coach standing on a sled) increases friction. - **Coefficient of Friction**: - Ratio describing the force required to overcome friction compared to the force holding surfaces together. 5. **Rolling Friction**: - Resistance of a rolling object (e.g., tires or balls) on a surface. - **Lower** than static or kinetic friction. **Summary Points:** - **Acceleration**: Change in velocity due to force; harder with higher mass. - **Reaction Forces**: Opposite and equal forces allow movement (e.g., ground reaction force). - **Friction**: - Static \> Kinetic. - Rolling friction is minimal compared to sliding friction. - Surface texture and applied force impact the frictional force.