Biomechanics Fundamentals: Levers, Torque, Forces, and Stress

Flashcards covering lever types, mechanical advantage, torque, gravity and weight, Newtonian mechanics, forces acting on the body, stability, and stress concepts from the lecture notes.

What are the three components of a lever system in biomechanics?

Axis/fulcrum, lever arms, and the forces or effort.

What is Mechanical Advantage (MA) in lever systems?

MA = length of force arm / length of resistance arm.

What does a mechanical advantage greater than 1.0 indicate in terms of muscle effort?

The applied (muscle) force can be smaller than the resistive force to produce the same torque.

What does a mechanical advantage less than 1.0 indicate in practical terms?

A disadvantage; the muscle must produce a greater force to achieve the same torque.

Describe a First-Class Lever arrangement.

The axis/fulcrum is between the muscle (effort) and the load (resistance); forces act on opposite sides of the fulcrum.

Describe a Second-Class Lever arrangement.

The load (resistance) is between the axis and the effort; axis is at one end; designed for lifting with MA > 1.

Describe a Third-Class Lever arrangement.

The effort (force) is between the axis and the resistance; designed for range of motion with MA < 1.

Which lever class is most common in human joints?

Third-Class Lever.

What is Torque?

The rotary effect of a force about an axis; units are Newton-meters (Nm).

What is the formula for Torque?

Torque = Force × Distance (moment arm).

What is a moment arm?

The perpendicular distance between the line of action of a force and the axis of rotation.

What is the acceleration due to gravity on Earth (g)?

Approximately 9.81 m/s^2 (downward).

What is Weight in biomechanics?

Weight = mass × gravity (g ≈ 9.81 m/s^2).

What happens under zero gravity conditions?

g = 0; effectively no weight.

Who is considered the father of mechanics?

Sir Isaac Newton.

What are Newton’s Laws used to analyze in biomechanics?

Forces and motion in mechanical systems.

What are the branches of rigid body mechanics?

Statics (rest/constant velocity), Kinematics (description of motion), Dynamics (acceleration), Kinetics (causes of motion).

What is Statics in this context?

Rest or constant velocity (no acceleration).

What is Kinematics in this context?

Description of motion (displacement, velocity, acceleration).

What is Dynamics in this context?

Acceleration.

What is Kinetics in this context?

Causes of motion (forces and torques).

What are Ground Reaction Forces (GRF)?

External forces exerted by the ground on the body.

What forces act on the human body according to the notes?

Gravity, GRF, Friction, Fluid forces (e.g., air), and Muscle forces.

What is Friction as described in the notes?

The horizontal component of the ground reaction force (GRF).

What factors increase stability according to the notes?

Increase body mass, increase friction, increase base of support, height of CG, and the horizontal position of CG relative to the base of support.

What is stress in biomechanics?

Stress s = F / A (internal force divided by cross-sectional area).

What are the main types of mechanical stress?

Compressive, Tensile, Shear, Bending, and Combined.

Describe Compressive Stress.

Compression: shortening of an object in the direction of the applied force.

Describe Tensile Stress.

Tension: elongation or stretching along the direction of the force.

Describe Shear Stress.

Forces acting parallel to a surface causing sliding between layers.

Describe Bending Stress.

Compression on one side and tension on the other due to off-center loading.

Why are most human joints considered third-class levers?

They are designed for a large range of motion; the muscle force acts between the axis and the load, yielding MA < 1.

How do you calculate torque in the dumbbell-holding example (45 N at 0.3 m)?

Torque = F × d = 45 N × 0.3 m = 13.5 Nm.

What force is required from elbow flexors to hold a 45 N dumbbell with a 0.03 m moment arm?

450 N.

What force is required from the deltoid to hold a 70 N dumbbell with a 0.5 m moment arm and a 0.05 m deltoid moment arm?

700 N.

What is the unit for torque and what does it represent?

Newton-meters (Nm); it represents the rotational effect of a force about an axis.