Levers & Center of gravity & Stability
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| What is a lever? | A simple machine consisting fo a relatively rigid bar like body that can be made to rotate about an axis
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| First class lever | Motive force and resistance force are on opposite side of the axis (F↓ ▲ R↓)
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| Second class lever | Motive force and resistance force are on the same side of the axis BUT resistance force closest to axis
( ▲ R↓ F↓)
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| 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↓ )
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| 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).
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| 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)
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| 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)
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| Long distance levers = ? | high risk injury
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| Ligaments close to the center of the joint need what? | larger force
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| Center of gravity (CG) | the point around which a body’s weight is
equally balanced or distributed in all directions
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| Center of mass (CM) | the point around which a body’s mass is
equally balanced or distributed in all directions
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| Where can the center of gravity lay? | inside and outside the body
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| CG inside the body | if body if homogeneous in density & symmetrical (anatomical position)
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| CG outside of body | not within the boundaries of the body
(fosbury flop)
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| Why is the CG of interest in the study of human bio-mechanics | It serves as an index of total body motion
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| CG↓ relative to body down to toes | way above the center of gravity
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| CG↓ low as possible | the higher you reach
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| CG↓ is high | the lower you reach
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| How might CG get even lower once you are in the air? | bring arms down (lower mass)
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| What does center of gravity obey? | The Laws of Motion
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| Balance | ability to control equilibrium
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| Stability | Resistance to the distribution of equilibrium
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| Factors affecting stability | size, base support, height of CG
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| Size | more mass, more inertia, more resistance to change
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| Relation of CG to base of support | if line of the CG falls within the base of support, stability results
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| Height of CG | higher CG - lower stability
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| Base of support | Area bound by the outermost regions
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| 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
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Created by:
rmart11
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