Gravity And BOS.pptx

Gravity not only pulls on mass but also on light. Albert Einstein discovered this principle. If you shine a flashlight upwards, the light will grow imperceptibly redder as gravity pulls it.
The base of support (BOS) refers to the area beneath an object or person that includes every point of contact that the object or person makes with the supporting surface.

1. MECHANICS: GRAVITY Presented By- Dr. Manisha Yadav (PT) MPT(Neuro) BOS

2. Content Introduction of Gravity Center of Gravity (COG) Line of Gravity (LOG) BOS

3. Introduction ‘’Gravity is force by which all the bodies are attracted to earth.’’ It is the most consistent force encountered by human body and behaves in a predictable manner. Gravitational Force is always directly vertically downward toward the center of earth . For example:- a. From the standing position the heels can be raised from the ground by the contraction of the calf muscles, working in opposition to the resistance of gravity, provided the force of their contraction exceeds the force of gravity. b. The heels will remain raised as long as the force of the static contraction of the muscles is equal to that of gravity. c. The heels will be lowered to the ground by the action of gravity if the muscles relax.

4. Center of Gravity (COG) ‘’The COG is a imaginary point at which the mass of the object is concentrated.’’ OR ‘’It is the point through which the earth’s attraction effectively acts regardless of position of body.’’ I t may depend on the size, shape, structure, weight, and portion of the particular object. Object :- S ymmetrical objects A symmetrical objects Rod

5. Symmetrical objects Asymmetrical objects Rod The symmetrical objects will have the COG at the center of the object. In asymmetric object the COG is located in the heavier end where the mass is concentrated. In a rod the COG is located near to the upper end, if it is vertically placed and the same will be near to the ground if it is horizontally placed due to its height, weight difference, and the weight transmitted area

6. The center of gravity (COG) of human body lies approximately anterior to the second sacral vertebra of an adult. Beacause body proportional change with age ,the COG of child is higher thanthat of an adult. In Human body COG

7. Line of Gravity (LOG) The imaginary vertical line passes through the center of gravity is called as ‘’line of gravity’’. It will change with the positional changes. When the human body is in fundamental standing position, the line of gravity(LOG) pass through vertex and a point between the feet, level with transverse tarsal joint.

8. In Human Body LOG pass through :-

9. BASE OF SUPPORT (BOS) The base of support means the area supported beneath the object. Whenever the base of support is more the stability will be more. Greater the BOS lower the COG of any object. 1 BOS α —----- COG

10. For example , The fundamental position of standing the BOS is lesser than the lying, so COG in the standing position it is in the higherlevel whereas in the lying posture it will be just near to the ground as a result lying posture is more stable than the any other fundamental position and also it can be maintained for the longer period.

11. In case a cube the face on which it rests is the base. Where as the effective base of a chair may be considered as the area bounded by the lines joining the legs.

12. The stability is directly proportional to BOS and inversely proportional to COG. Stability α BOS 1 Stability α ——— COG

13. THANK YOU