Fundamental Concepts and Principles of Mechanics Chapter 3 Fundamental Concepts and Principles of Mechanics

Mechanics Science concerned with the effects of forces acting on objects (body) body: focus of the analysis human body individual body segment specific tissue / anatomical site balls, pucks implement: bat, stick, club

Mechanics Science concerned with the effects of forces acting on objects (body) Rigid-body mechanics Deformable body mechanics Fluid mechanics Relativistic mechanics Quantum mechanics

Rigid Body Mechanics Acceptable for analyzing gross movements Assumptions body does not deform by bending, stretching or compressing segments are rigid links joined by frictionless hinges at joints

Basic dimensions in mechanics Describe someone out for a run

Basic dimensions in mechanics Describe someone out for a run Kinematics How far did she run? How long to run that far? How fast was she? How big is she? Kinetics What friction under her feet? What forces on her joints? What tension in her muscles?

Length Measure to describe Feet, inches, miles location at a particular point in her run how far she ran Feet, inches, miles Systeme Internationale d’Unites (SI) meter 1 m = 3.28 feet = 39 inches

Time Measure to describe how long it takes her seconds, minutes, hours, days, months, years Systeme Internationale d’Unites (SI) second (s)

Length & time = motion Space to move in and time during which to move speed & velocity==> length per unit of time miles per hour m / s acceleration m/s/s

Inertia Inertia Who is harder to start or stop moving resistance to a change in state of motion Who is harder to start or stop moving Olympic weight lifter Olympic gymnast

Inertia Inertia Who is harder to start or stop moving resistance to a change in state of motion Who is harder to start or stop moving Olympic weight lifter: has more inertia Olympic gymnast

Inertia and Mass Inertia Mass resistance to a change in state of motion Mass the quantity of matter a body possesses quantifies inertia (the measure of inertia) Greater mass, greater inertia resistance to change state of motion units are kilogram (kg) or slug (English) Not the same as weight

Importance of Inertia & Mass Provide another example of changing motion in sport exercise workplace

Importance of Inertia & Mass Provide another example of changing motion in Sport: size expectations of different positions (ie interior defensive linemen) Exercise: alter mass to be moved to increase load on NMS system (ie push-up) Workplace: alter mass of components to reduce load (ie cement bags, engine blocks)

3 basic dimensions All that is needed to describe Length Time Mass Force: defined from the above a push or pull acting on a body All that is needed to describe and explain the motion of objects

Force Force: a push or pull acting on a body that causes or tends to cause a change in the linear motion of the body Characteristics of a force magnitude direction point of application. line of action Net Force: resultant force (overall effect of multiple forces acting on a body) Example: push from side and front = at angle

Sir Isaac Newton 1642-1727 Proposed fundamental laws that are the basis of modern mechanics 3 laws of motion law of gravitation Click here to see more on Newton

Newton's First Law of Motion Law of inertia - a body in motion will stay in motion and a body at rest will stay at rest unless acted upon by a net external force. Newton I & whiplash injury Homework: read & summarize See video next slide

Newton I in action (with nasty consequences)

HANS device The HANS® (Head And Neck Support) Device was originally designed to limit the extreme front to back and side-to-side movement of the head and neck during a violent crash. Using a collar and yoke system made of carbon fiber and Kevlar, the device is connected to the helmet with a series of quick connect tethers. The HANS® Device is worn around the neck and down the front of the shoulders, underneath the safety belts of the shoulder harness. This allows for normal movement of the head and helmet, but limits the extreme movement of the head and neck that is so common in the rapid deceleration during a crash HANS device Click image for more info

Newton's 3rd Law of Motion Law of action-reaction - for every action, there is an equal and opposite reaction There are two bodies involved when force is exerted The force on each body is the same size, but in opposite directions true even when the bodies are of significantly different mass Sumo with my boys Gymnast on bar Skip video

Newton III in action

Newton's 2nd Law of Motion Law of acceleration - an unbalanced force applied to a body causes an acceleration of that body with a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body's mass. Newton & Swimming

F = ma  Unbalanced force causes a change in motion (an acceleration) CAUSE-EFFECT relationship

During running, if a runner swings his arms across his body, there is a compensatory increase in pelvic rotation. It is more efficient and better for the pelvis and pelvic musculature if the runner moves his arms parallel to the motion in which he is running.

Click here to go to a site with practice problems on forces, and a review of Newton’s 3 Laws

Units of Force Metric system (systeme internationale) English system Newton (N) the amount of force necessary to accelerate a mass of 1 kg at 1 m/s2 English system pound (lb) the amount of force necessary to accelerate a mass of 1 slug at 1 ft/s2 equal to 4.45 N

It is important to know how Newton’s 3 laws apply. Click here to go to a site on Newton’s Laws suggested by Mike Dawson (Spring, 2000). See if you can pick out the errors in the presentation.

Of Newton... Alexander Pope wrote: Nature and Nature's Laws lay hid in night: God said, "Let Newton be!" and all was light Quiz on Newton’s Laws

Newton's Law of Universal Gravitation Law of gravitation - all bodies are attracted to one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. Click here for some problems to solve

g = Gravitational acceleration The acceleration of gravity - 9.81 m/s2 (- 10 m/s/s) Negative sign??? indicates that the acceleration caused by gravity is directed downward or toward the center of the earth The earth sucks Amusement Park Physics Newton and the Apple: click here to see more

Terminal Velocity

Weight Weight the amount of gravitational force exerted on a body F = m g W = m g W: weight (wt) (units: N or lbs) m: mass of the body (units: kg) g: gravitational acceleration (units: m/s/s) As the mass of a body increases, its’ weight increases proportionally

Weight is a force As a force, weight characterized by magnitude proportional to mass direction ALWAYS downward point of application at center of gravity of the body Units: Newtons or pounds (mass???)

A problem often encountered in KNR 282. We all get heavier as we get older because there's a lot more information in our heads." - Vlade Divac Click here for another great site on Newton’s Laws