Chapter 8 Biomechanics Flashcards
Kinetics
forces causing movement (torque, gravity, friction etc)
Kinematics
Time, space, mass of a moving system
Force
any action or influence that moves and object
Vector
quantity having both magnitude and direction
Inertia
Property of matter that causes it to resist any change of its motion
Torque
Tendency of force to produce rotation about an axis
Friction
Force developed by 2 surfaces
Velocity
vector that describes displacement and is measured in units (How fast something moves)
Laws of Motion
- Inertia
- Acceleration
- Action-Reaction
Law of Inertia
Object at rest tends to stay at rest, object in motion tends to stay in motion (Ex. Your body when riding in a car)
Law of Acceleration
- Amount of acceleration depends on the force applied to it
- Force is needed to change direction
- Acceleration is inversely proportional to the mass of an object
(Ex. Kicking a ball and how far it goes)
Law of Action Reaction
For every action there is an equal and opposite reaction
Ex. Jumping on a trampoline
Two actions that describe force
Scalar and Vector
Scalar
Describes magnitude of force
Vector
Describes both magnitude and direction of force
Resultant Force
Net effect of two divergent forces (Ex. anterior posterior portions of deltoids flexing shoulder)
Force Couple
Two forces act in an equal but opposite reaction producing rotation around an axis
Torque involved in PT
Greatest strength at 90 degrees. Torque decreases as angle increase or decreases
BOS, COG and LOG
Base of support, Center of Gravity and Line of Gravity
stable Equilibrium
To disturb object, you must raise the center of gravity
Unstable Equilibrium
When only a slight force is needed to disturb an object
Neutral equilibrium
Objects COG is neither raised nor lowered when disturbed
Ways to increase stability
Lower COg and widen BOS
1st class lever
FAR. Axis between force and resitance. Designed for balance (ex. sternocleidomastoid)
2nd class lever
ARF. Axis opposite force, resistance in the middle. Designed for power (ex. plantar flexion on tip toes)
3rd class lever
AFR. Axis opposite resistance, force in the middle. Designed for ROM (ex. Elbow Joint)
Most common lever system in the body
2nd class lever
Mechanical advantage when carrying an object
Hold closer to body to reduce amount of resistance
MA fromula
Force Arm / Resistance Arm
