Notes on Lever Systems and Physics Newton's Laws

Levers Discussion Overview

  • Brief casual conversation at the beginning regarding weekends.

Classes of Levers

  • First Class Lever:

    • Axis located in the middle.

    • Example: Seesaw.

  • Second Class Lever:

    • Force arm always longer than resistance arm, cannot have mechanical advantage below one.

  • Third Class Lever:

    • Resistance arm always longer, mechanical advantage always below one.

Torque and Mechanical Advantage

  • Torque Definition:

    • Torque = Force × Moment Arm.

    • Moment arm refers to the distance from the axis of rotation to where the force is applied.

  • Mechanical Advantage Calculation:

    • Mechanical Advantage = Force Arm / Resistance Arm.

    • Examples given:

    1. Both arms equal (10/10) yields MA = 1.

    2. Different lengths lead to different MA values.

Balanced Lever Systems

  • A balanced lever system occurs when:

    • Torque on one side equals torque on the other.

    • Example Calculations:

    • 20 (force arm) × 10 = 200 (torque).

    • 20 (force arm) and 5 (resistance arm) = MA of 4.

    • 5 (force arm) and 15 (resistance arm) = MA of 0.33.

  • Emphasis on importance of understanding whether one is above or below an MA of one based on the class of lever.

  • Second Class Lever:

    • Focus on production of force, all MAs above 1.

Manipulating Arms for Mechanical Advantage

  • Shortening Resistance Arm:

    • Increases mechanical advantage but moves the resistance less distance.

  • Positioning Resistance Closer to Axis:

    • Less mechanical advantage but allows for greater distance moved.

  • Importance of contextual decisions when manipulating lever arms for specific goals.

Third Class Lever Characteristics

  • Examples and calculations:

    • Force arm of 10 and resistance arm of 20 yields MA of 0.5, indicating higher force needed to balance.

Formula for Balanced Lever System

  • Equation:

    • F × FA = R × RA

    • Implications of torque balance on either side.

  • Example Calculation:

    • With a force arm of 0.1 meters, a resistance of 45N, and a resistance arm of 0.25 meters, required force = 112.5N.

Outer Lever System

  • Built for speed and range of motion at the expense of force.

  • Short force arms result in higher speed and range of motion.

Applications in Human Movement

  • Biceps and Triceps:

    • Biceps force arm is short; triceps are shorter for maximum efficiency.

  • Discusses importance of lever lengths in sports context: throwing balls, swinging bats, etc.

Lever Systems in Sporting Contexts

  • Different lever lengths lead to effects on performance:

    • Longer lever arms achieve greater velocity but require precise management.

    • Specific applications like tennis, baseball, and gymnastics demonstrate different leverage requirements.

Wheel and Axle System

  • Functionality:

    • Wheel and axle act as levers with the fulcrum at the center.

    • Applications in movement, e.g., a car using its axle to rotate wheels.

    • Mechanical Advantage = Radius of Wheel / Radius of Axle.

Pulley Systems

  • One pulley has MA of 1. Combined pulleys increase MA.

  • Example: With 3 pulleys a 50kg resistance becomes 50/3.

Lower Extremity and Levers

  • Ankle as Second Class Lever:

    • Works in conjunction with a pulley for plantar flexion.

  • Focus on the importance of joint stiffness in performance.

Newton's Laws of Motion

  • First Law (Inertia):

    • Object remains at rest or in motion unless acted upon.

  • Second Law (Acceleration):

    • Acceleration is directly proportional to force and inversely proportional to mass.

    • Acceleration defined as a change in velocity.

  • Third Law (Reaction):

    • For every action, there's an equal and opposite reaction (ground reaction force).

Conclusion and Next Steps

  • Reminder about upcoming exams and study methodologies.

  • Importance of preparing and techniques to optimize performance in tests based on material covered.