Center of gravity and stability

4th section kinesiology

1. Center of gravity and Stability Kinesiology practical Mostafa elwan

2. Center of gravity (COG) : Center of gravity (COG) : is an imaginary point that the body weight can be assumed to be concentrated and equally distributed, around which body can rotate freely in all direction. The point where a body may be hung without rotating . The point at which summation of all moments equal zero The point where the weight of the body is concentrated. Its symbol is COG , COM or CG . Anatomically ; This point can be represented by the point of intersection of the three cardinal body planes (Sagittal , frontal and transverse ). Anti- Clockwise Moment = Clockwise Moment

3. Is Cog fixed ???

4. Location of Center of Gravity : A. in Regularly-Shaped Bodies:

5. The center of gravity can be located within or outside the body depending on the bodies configuration and position; it is inside an object when the object is uniform and outside the object when it is not uniform.

6. Location of Center of Gravity : b. in Irregularly-Shaped Bodies: The COG will be nearer the larger and heavier end

7. Location of Center of Gravity : in Human being • It’s is located anterior to the second sacral vertebra in the anatomical position (standing) in normal adult person . In new born: above umbilicus . At six month: at the level of six thoracic vertebra . At two years: at the level of umbilicus . At five years: below the level of umbilicus. Adult: anterior to the second sacral vertebra.

8. Factors affecting Cog location: Age : relatively higher in infants and children compared to adults Sex – higher in males than in females Height Body Type – Mesomorph, Endomorph & Ectomorph Weight : Added (pregnancy) or Subtracted (amputation) Position of Any Segment in Relation to Total Body Segments: flexion of right arm leads to movement of COG upward, forward and to the right.

9. Location of center of gravity shifts whenever the person shifts position

10. Determination of COG Location Total Body COG The total body COG can be determined using mathematical or laboratory methods . A) Total Body COG: Mathematical Method Laboratory Method B) Determination of Segmental Body COG

11. A ) Total Body COG : 1) Mathematical Method a. Croskey formula In male : = height of COG measured from heel In female: = height of COG measured from heel E.g.: = 98.87cm   b. Palmar formula regardless to the subject sex +1.4 = height of COG measured from heel E.g.: +1.4 = 99.43cm  

12. A) Total Body COG : 2) Laboratory Method Board and Scale Method

13. B) Determination of Segmental Body COG Approximately 4/7 of the segment length measured from the distal end . E.G.: 30cm *4/7 =17.14cm

14. Line of Gravity (LOG): is an imaginary vertical line passing through the COG toward the center of the earth When the human body is in the standing position the line of gravity passes from the vertex through the 2nd sacral vertebra to just in front of the ankle joint and between the feet.

15. Base of support (BOS) is that part of a body that is in contact with the supporting surface .

16. Cog and Base of support

17. Examples:

18. You Must know Equilibrium: is a state of balance in which all forces are equal . Balance :is the ability to control equilibrium during changing body’s position . Stability: is a measure of the body’s ability to maintain its original position .

19. EQUILIBRIUM Definition ; Equilibrium is a state of balance in which all forces are equal. A body is said to be in equilibrium when the resultant of all forces acting upon it is zero . G T F M

20. 1-Stable Equilibrium The lower the COG and the wider the base of support the more and more equilibrium will be established, E.g. person lying flat on the floor . when it returns to its original position after given a small displacement Example : The Traffic Cone Low Centre of Gravity Wide base & lower COG

21. 2- Unstable equilibrium If the object is displaced slightly and it tends to increase its displacement The COG drops to a lower point when compared to the original starting position e.g. a cone An object becomes unstable when its Centre of Gravity falls outside of the object’s base.

22. 3- Neutral equilibrium; if it comes to rest in a new position without a change in the level of the COG either upwards or downwards E.g. A ball

23. Example: .

24. Conditions of Equilibrium 1- If the body is at rest, with the velocity equaling zero , it is said to be in static equilibrium. ∑F = 0, ∑M = 0 2- If the constant velocity is not zero, the equilibrium is called dynamic equilibrium according to Newton's second law  of motion is F = ma, or force is equal to mass times acceleration. ∑ F = 0 , f=m*a , A=  

25. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface ( The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Also, stability increased if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE: Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age

26. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface(The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Especially if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE: Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age

27. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface(The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Also, stability increased if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE: Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age

28. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface(The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Also, stability increased if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE: Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age

29. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface(The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Also, stability increased if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE: Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age

30. Factors affecting stability COG height ( the Lower the COG, the Greater will be the body Stability. Base of support (BOS) surface(The greater the BOS , the greater the stability.) BASE OF SUPPORT (BOS): An greater the BOS will be increase in the stability. Also, stability increased if the increase in BOS in the direction of applied force. Line of gravity :For balance to be maintained, it is essential that the line from LOG should fall within the BOS PROPERITIES OF SUPPORTING SURFACE : Friction (increase stability via friction) Softness of the supporting surface(soft mattress , the less the stability.) Inclination of the supporting surface(The greater the inclination, the less the stability) 5. Segmentation Principle If there is deviation of a part of the body to certain direction, there is another compensator deviation of another part of the body to the opposite direction to maintain balance during this position 6. HE PERSON HIMSELF :Mass , Vision, Physical & Emotional State , Pain and Age