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Biomechanics

Levers & Center of gravity & Stability

QuestionAnswer
What is a lever? A simple machine consisting fo a relatively rigid bar like body that can be made to rotate about an axis
First class lever Motive force and resistance force are on opposite side of the axis (F↓ ▲ R↓)
Second class lever Motive force and resistance force are on the same side of the axis BUT resistance force closest to axis ( ▲ R↓ F↓)
Third class lever (most common) Motive force and resistance force are on the same side of the axis BUT motive force is closest to axis ( ▲F ↑R↓ )
The main advantage of 3rd class lever? A force can move a resistance through a large range of motion when the force arm (fa) is shorter than the resistance arm (ra).
Law of the lever for long arm A small force can have a large torque or moment of rotation if the lever arm is long (long arm = less force)
Law of the lever for short arm the force must be large to achieve the same moment of rotation if the lever arm is short (short arm = more force)
Long distance levers = ? high risk injury
Ligaments close to the center of the joint need what? larger force
Center of gravity (CG) the point around which a body’s weight is equally balanced or distributed in all directions
Center of mass (CM) the point around which a body’s mass is equally balanced or distributed in all directions
Where can the center of gravity lay? inside and outside the body
CG inside the body if body if homogeneous in density & symmetrical (anatomical position)
CG outside of body not within the boundaries of the body (fosbury flop)
Why is the CG of interest in the study of human bio-mechanics It serves as an index of total body motion
CG↓ relative to body down to toes way above the center of gravity
CG↓ low as possible the higher you reach
CG↓ is high the lower you reach
How might CG get even lower once you are in the air? bring arms down (lower mass)
What does center of gravity obey? The Laws of Motion
Balance ability to control equilibrium
Stability Resistance to the distribution of equilibrium
Factors affecting stability size, base support, height of CG
Size more mass, more inertia, more resistance to change
Relation of CG to base of support if line of the CG falls within the base of support, stability results
Height of CG higher CG - lower stability
Base of support Area bound by the outermost regions
What can increase a body's stability? -increase body mass -increase friction (body & contact surface) -increase size of the base of support in direction of external force -horizontally position CG near edge of base support on the side of the external force -lowering body's CG
Created by: rmart11
 

 



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