Chapter 8: Basic Biomechanics
Levers
-3 points determine type of lever and for which kind of motion is best suited: 1. Axis (A): AKA fulcrum, is the point of rotation. 2. Point of Force (F): AKA effort, causes lever to move usually muscular. 3. Point of Resistance (R): AKA load, must overcome for motion to occur and can include the weight of the part being moved, the pull of gravity on the part, or an external weight being moved by the body part.
Laws of Inertia
-A body in motion tends to remain in motion at the same speed in a straight line unless acted on by a force. -A body at rest tends to remain at rest unless acted on by a force. -Muscles produce force to start, stop, accelerate, decelerate, and chance the direction of motion. -The greater an object's mass, the more force needed to significantly change an object's inertia. -Force is required to change inertia
Law of Acceleration
-A change in the acceleration of a body occurs in the same direction as the force caused by it. The change in acceleration is directly proportional to the force causing it and inversely proportional to the mass of the body. -Mass affects the speed and acceleration in physical movements.
Torque
-AKA moment of force. -The ability of force to produce rotation around an axis. -Can be thought of as rotary force. -Amount of torque a lever has depends on the amount of force exerted and the distance it is from the axis. -Determined by multiplying amount of force (force magnitude) by force arm (perpendicular distance between location of force application and axis). -Greatest when the angle of pull is at 90 degrees.
Wheel and Axle
-Another type of simple machine. -Lever in disguise. -Consists of a wheel (crank) attached to and turning with an axle. The wheel is connected to a smaller wheel and typically is used to increase the force exerted.
Law of Reaction
-For every action, there is an opposite and equal rxn. -The strength of the rxn is ALWAYS equal to the strength of the action and occurs in the opposite direction.
Eccentric
-Force applied in a direction not in line with the center of rotation of an object with fixed axis.
Inclined Plane
-Greater the force, the greater the speed. -Exchanges increased distance for less effort.
Second-Class Lever
-Produce force movements, since large resistance can be moved by a relatively small force. -A lot of power and force, but not a lot of distance.
Pulleys
-Single pulley's fxn to change effective direction of force application. -Consist of grooved wheel that turns on an axle with a rope or cable riding in the groove.
Third-Class Lever
-Speed and distance. -Produce speed and ROM movements. -Requires a great deal of force to move even a small resistance.
First-Class Lever
-The axis is located between the force and the resistance. -Requires more resistance. -Produce balanced movements when axis is midway between force and resistance (e.g. seesaw). -Produce speed and range of motion when axis is close to force (triceps in elbow extension). -Produce force motion when axis is close to resistance (crowbar).
Stability: Center of Gravity
-The balance point of an object at which torque on all sides is equal. -It is also where all planes intercept, the midline S2.
Stability
-The resistance to a: Change in the body's acceleration Disturbance of the body's equilibrium -Stability is enhanced by determining body's COG and appropriately changing it. -To control equilibrium and achieve balance, stability needs to be maximized.
Concurrent Force
-Two or more forces acting on a common point must push/pull in different directions. -Resultant force: overall effect of these two different forces
Stability: State of Equilibrium
-When an object is balanced, and all torques acting on it are even. -How secure it is depends on the relationship between the object's COG and its BOS.
Force
-muscles are the main source of force that produces or changes movement of the body segment, or some object thrown, struck, or stopped. -Strong muscles are able to produce more force than weak muscles. -Linear forces, parallel forces, and concurrent forces.
Factors That Change Class
1. Resistance changes 2. Gravity
Stability: Line of Gravity
An imaginary vertical line passing through the COG toward the center of the earth.
Parallel Force
Occur in the same plane in the same or opposite direction
Force Couple
Occurs when two or more forces act in different directions, resulting in a turning effect.
Stability: Base of Support
Part of the body that is in contact with the supporting surface.
Inertia
Resistance to action or change
Levers: Force Arm (FA)
The distance between the force and the axis
Levers: Resistance Arm (RA)
The distance between the resistance and the axis.
Linear Forces
Two or more forces are acting along the same line.
