PT PAP 101 - Force Systems PDF

PT PAP 101- FORCE SYSTEMS September 10, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this Lecture, the student should be able to Define...

PT PAP 101- FORCE SYSTEMS September 10, 2024 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH SEIENCES Objectives At the end of this Lecture, the student should be able to Define force Explain Mechanobiology Define Newtons law of Motion Explain Different types of force systems. Describe the implications of force systems in the human body. Explain Anatomic pulleys and its implications in human body. Understand angle of muscle pull  Mechanobiology It is the study of how cells sense the mechanical forces of the physical microenvironment and what molecular cascades and cellular responses ensue when they are sensed. Mechanobiology may greatly facilitate the development of new therapies that control mechanical forces and thereby specifically induce desired molecular, cellular, tissue, and/or organ formation, changes, or repair” in rehabilitation science.  Force Force is that which pushes or pulls through direct mechanical contact or through the force of gravity to alter the motion of an object Internal forces are muscle forces that act on various structure of the body External forces are those outside the body Weight, gravity, air or water resistance, friction, or forces of other objects acting on the body  NEWTON’S LAW Law of Acceleration It states that the acceleration of an object is proportional to the unbalanced forces acting on it and inversely proportional to the mass of that object a=F/m Law of Equilibrium It states that an object will remain at rest or in uniform motion unless acted on by an unbalanced force Law of Reaction For every action there is an equal and opposite reaction  Linear Force System Linear force system exists whenever two or more forces act on the same object and in the same direction, line or plane All forces act along the same action line  Concurrent Force System Forces applied to an object may not be in a line but have action lines that lie at angles to each other Two or more forces acting at a common point of application but in different (divergent) directions/angle. Composition of Forces: Net effect of these two divergent forces is called the Resultant force, and appears to occur at the common point or at the point of intersection and found out through the process known as composition of forces RF Man A and B are pulling the block each at right angels with a force of 75lb each Action lines AB- A on block and BB-B on block are in different directions but are commonly applied through the COG of the block  The net effect or resultant of the two pulls will be in a line that lies between the men Vector AB and BB are drawn to scale maintaining a 90 angle between them Line AB' and BB' are drawn parallel to AB and BB forming a polygon The resultant force R lies at the intersection of AB and BB and its action line and magnitude are drawn so that the arrow head lies at the intersection of lines AB' and BB'  Linear force system Cervical Traction-Linear force Psoas major and iliacus muscles act along the same action line, point of application, and same direction- Linear force Trapezius muscle on both sides act along the same action line, but in opposite directions. 11  Concurrent force system Action of sternal and clavicular parts of the pectoralis major 12  Application in Human Body Divergent muscle pulls : Concepts of concurrent force system can be used to determine the resultant of two or more segments of one muscle or two muscles when they have a common attachment Example: Deltoid consists of AD,PD,MD Anterior portion of the deltoid muscle –AD Posterior portion of the deltoid muscle -PD acting on the humerus AD & PD form the polygon  R is the resultant force vector (AD & PD) for the above polygon R represents the sum of AD and PD The deltoid is composed of the middle segment MD R and MD coincide and the common point of application they are part of the same linear force system The resultant in a linear force system is the arithmetic sum of vectors R and MD Vector Fms produces abduction of the Fms=R+MD arm  Pectoralis major – sternal & clavicular portion CPM = Clavicular portion of PM SPM = Sternal portion of PM Fms = Net force or resultant which brings about adduction and medial rotation of humerus  Parallel force system When all the forces are coplanar (acting at the same plane), at two different points, and parallel to each other, but do not share the same action line Hamstring muscles components: medial (semitendinosus & semimembranosus) and lateral (biceps femoris) 16  Force of Friction 1. Friction may exist on an object whenever 2 objects touch each other. 2. Shear force is a force that is applied parallel to contacting surfaces in the direction of the attempted movements. 3. Friction has magnitude only when there is a shear force applied to an object; that is friction has magnitude only when 2 contacting objects move or attempt to move on each other 4. The action line of friction forces always lies parallel to the contacting surfaces 5. The direction of the force of friction is always opposite to the direction of the movement 19  Use of friction in physiotherapy Moving patient in bed Massage Suspension therapy Sit to stand on mat 20 21