Biophysics Chapter 2: Equilibrium and Muscles

Biophysics

• Biophysics encompasses various fields, including bioenergetics, spectroscopy, Brownian motion, diffusion, bioacoustics, and molecular action.
• Other important concepts include entanglement, magnetic imaging, and quantum mechanics.
• Key figures in biophysics include Einstein.

Chapter 2: Equilibrium and Muscles

• Covers concepts like Force & Torque, Static & Equilibrium, Equilibrium in the Human Body, Muscles and Tendons, Levers, Back muscles, and Elbow.
• Illustrations of topics like a rock balanced precariously on a ledge show the importance of calculating and understanding various forces in establishing equilibrium.

Force & Torque

• Force and torque are fundamental concepts in physics.
• Force is a push or pull that alters an object's state of motion; it is measured in Newtons (N).
• Torque is the twisting or turning effect due to a force applied at a distance from an object's rotation axis, measured in Newton meters (N⋅m).
• Torque is calculated by multiplying the perpendicular force by the distance from the rotation point to the force application point.
• The magnitude of torque is equal to the applied force multiplied by the perpendicular distance to the pivot point.

Static and Equilibrium

• A body is static if its linear and angular velocities are zero.
• A body is in equilibrium if the resultant external forces and torques are zero.
• Stable equilibrium means the body returns to its original position when slightly displaced and is a key concept in physical systems like the human body.

Center of Mass and Stability

• The center of mass is the average position of all parts of an object, weighted by their masses.
• For a uniform gravitational field, the center of gravity and center of mass coincide.
• Stability depends on the position of the center of gravity relative to the base of support. A lower center of gravity enhances stability.

Conditions for Stable Equilibrium

• A body is in stable equilibrium if a disturbance produces a restoring force or torque that tends to return the body to its original position.
• If the center of mass is above the base of support, the body is typically stable. If the center of mass is below the base, it is unstable.

Static, Stable Equilibrium, and Unstable

• Static equilibrium occurs when the net force and torque on an object are zero.
• Stable equilibrium occurs when a disturbance causes a restoring force that returns it to its initial position.
• Unstable equilibrium is when a disturbance causes a force or torque that moves the object further from its initial position.

Equilibrium in the Human Body

• The center of gravity of an upright human with arms at the sides is approximately 56% of their height from the soles of the feet.
• The center of mass position changes with posture and body configuration shifts.
• Uneven loads cause postural adjustments to maintain balance.

Muscles and Tendons

• Skeletal muscle movements are produced by thousands of parallel fibers.
• Muscle force depends on the number of contracting fibers.
• Tendons attach muscles to bones; most muscles have one tendon, while others, like biceps, have more than one.

Levers

• Levers are used to lift loads or transfer movement efficiently.
• They consist of a rigid bar that rotates around a fixed point (fulcrum).
• There are three classes of levers, distinguished by the relative positions of the load, effort, and fulcrum.
• Class 1 levers have the fulcrum between the load and effort.
• Class 2 levers have the load between the fulcrum and the effort.
• Class 3 levers have the effort between the load and the fulcrum

Elbow

• The elbow joint acts as a lever system.
• Muscles (like biceps and triceps) work in pairs to flex and extend the forearm.
• The force exerted by a muscle depends on the torque generated by the muscle.

Mandible as a Lever

• The mandible acts as a class III lever system.
• The temporomandibular joint (TMJ) serves as the fulcrum.
• The masseter muscle provides the effort to move the lower teeth relative to the bullet.

Back Muscles

• Good posture keeps the center of gravity over the feet.
• Bad posture often causes back strain because the center of gravity is not over the feet.