The Kinematics of Trauma Physics, light on the math

Axiomata sive leges motus Lex I: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare. Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. Lex III: Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi.

Definitions and Simplifications Dynamics An approach to physics that involves mathematical calculations to understand the motion of bodies. Answers are quantitative. Kinematics An approach to physics that aims to understand the motion of bodies with minimal math. “Goldilocks physics”

Definitions and Simplifications Mass=amount of matter Force=push or pull Velocity=distance/time Acceleration=change in velocity/time Weight=mass x gravitational acceleration Energy=the ability to do work

Definitions and Simplifications weight≈mass Density=mass/volume Higher density=higher energy transfer

Newton’s Laws of motion Objects in motion will stay in motion, and objects at rest will stay at rest unless acted on by an external force. (Inertia)

Newton’s Laws of motion Inertia Measured by an object’s momentum Momentum = mass x velocity Used to describe an object’s resistance to changes in motion

Newton’s Laws of motion An object’s acceleration is proportional to the force applied, and inversely proportional to its mass. (Force = mass x acceleration) Moving objects that are decelerated rapidly exert large forces

Newton’s Laws of motion Every action has an equal and opposite reaction (forces exist in pairs) The reaction may cause further actions Forces can begin in a straight line, and disperse, causing cavitations

Forces that cause trauma Compression (in-line) Contusions Penetrations Lacerations(in combination with friction) Dislocations Fractures

Forces that cause trauma Torsion (rotational) Dislocations Fractures

Forces that cause trauma Friction (tangential) Abrasions Lacerations(in combination with compression)

What injuries do you expect? Small group collaboration Think of as many injuries as you can. Compression Injuries? Torsion Injuries? Friction Injuries? Include type and location Explain where the forces involved originated

Pressure Pressure = Force / Area Pressure determines whether trauma is blunt or penetrating

Energy Can not be created or destroyed, only transferred or transformed Types of Energy Thermal Electromagnetic Chemical Mechanical

Injuries by energy type Electrical energy transforms into heat based on resistance to current flow. Heat energy does work on cells by denaturing proteins and vaporizing intracellular water. Chemical energy denatures proteins, and can transform into heat energy in the process. Mechanical energy does work on body structures by changing their position.

Electromagnetic Energy Voltage is the “push” behind electricity. Current is the amount of electricity. Aside from the nervous system, the human body is not a good conductor. High resistance means lots of energy transformed into heat.

Thermal Energy The human body is 70% water on average As water is changed to steam, it increases in volume 1700 times Protein denaturing= irreversible changes in chemical structure.

Chemical energy Most chemical burns are due to extreme pH. Acids donate protons Bases steal protons Too many or too few protons leads to protein denaturation.

Mechanical Energy Two components: kinetic and potential Kinetic is the energy of motion: Potential is stored energy due to height

Energy Relationships In any system, the mechanical energy is the sum of the potential and kinetic energies. Decreasing potential energy (falling) means increasing kinetic energy.

Energy Relationships Work and Energy are equivalent Energy transfer W=E W=Fd F=E/d Energy transfer Radiation Conduction Convection Work

What’s it all mean? Since velocity is squared: Stopping distance: Doubling speed = 4x force Tripling speed = 9x force Stopping distance: Shorter distances mean greater forces

Anatomical Concerns Most organs are not well secured within the body. Heart, kidneys and liver have massive blood supply

Anatomic Concerns Sudden shifts can shear the vessels connected to these organs Blunt trauma to these organs can cause massive contusions Penetrating trauma to these organs can cause life threatening loss of blood

Anatomical Concerns Brain floats inside a boney cage A sudden shift stops the skull first, which then stops the brain Vasculature on the surface of the brain is extensive As intracranial space fills with blood, where will it go?

Brain Vasculature

Anatomical Concerns Fragile body parts Lungs are only a single cell thick Sudden impact can cause “paper bag” effect Spleen and liver covered only with a thin layer of connective tissue Contusions and ruptures common GI tract is a series of “bags”

Anatomical Concerns Spinal curvature Forces can alter these curvatures Cervical and Sacral lordosis Thoracic kyphosis Forces can alter these curvatures

Special Considerations Some situations may: Alter the normal mechanics of the body Cause multiple phases of injury

Pneumothorax Breathing is accomplished by creating “negative pressure” Diaphragm contracts, reducing the pressure in the chest Air rushes in to equalize the pressure Holes in the lung or chest wall allow air into the chest cavity, rather than the lung

Blast Injuries Primary from absorbing the energy of the blast Secondary from being hit with flying objects Tertiary from being thrown against stationary objects

Motor Vehicle Collisions Two systems of vehicle plus passengers Total energy is the sum of the energies of the vehicles plus passengers Energy is transferred from vehicle to vehicle, and between passengers and vehicles.

Fall from height Longer falls mean more kinetic energy Terminal velocity reached at about 60 ft. Elastic surfaces will absorb some of the energy of the falling person Inelastic surfaces cause ALL of the energy of the fall to be absorbed by the body

Please email your answers to: QUIZ! Let’s see what stuck. Please email your answers to: cmehl@sheridanmemorial.net

Question 1 How many laws of motion did Isaac Newton posit?

Question 2 Which object has greater momentum? A speeding bullet A fully loaded ambulance at 10 mph

Question 3 List a type of injury that could be caused by each of the following: Compressional Force Torsional Force Frictional Force

Question 4 Which of the following is true regarding the magnitude of the forces involved in a vehicle collision? The mass of the vehicle is more important than the speed The mass of the vehicle is less important than the speed The area of collision matters the most Airbag deployment matters the most

Question 5 Which seatbelt will reduce the force of impact best? A seatbelt that does not flex A flexible seatbelt that stretches slightly No seatbelt

Question 6 What are the three causes of injury from explosions?

Question 7 How is it possible for electricity to cause burns?

Question 8 What determines whether an injury will be blunt or penetrating?

Question 9 Energy cannot be __________________ or ___________________, only ________________ or ______________.

Question 10 Why are motor vehicle collisions so damaging to the human body?

Please email your answers to: cmehl@sheridanmemorial.net