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Biomechanics
Levers & Center of gravity & Stability
| Question | Answer |
|---|---|
| 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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