03-02: Biomechanics Flashcards
Newton’s Laws of Motion: 1st Law
Law of Inertia: Tendency of an object to stay at rest or in motion
Newton’s Laws of Motion: 2nd Law
Law of Acceleration: Acceleration depends on strength of force (Force = Mass x Acceleration)
Newton’s Laws of Motion: 3rd Law
Law of Action/Reaction: Every action has an equal opposite reaction
Gravity
9.8 meters/sec (2)
Force
Vector quantities; Push or pull
Characteristics of Force
Magnitude, direction, point of application
Linear Force
Two or more forces acting along the same line
Parallel Forces
Occur in the same plane and same or opposite direction
A third force must be between the two parallel forces and must be of sufficient strength to counter the other two forces.
Concurrent forces
Two or more forces must act from a common point, but pull in two different directions; shown graphically using Parallelogram method
Resultant force
Net effect of concurrent forces
Force Couple
Two forces act in EQUAL but OPPOSITE direction resulting in turning; Force-Counterforce
Ex: Opening a jar
Torque
The ability of force to produce rotation about an axis
Torque formula
- Force x Distance
- Depends on amount of force and distance of the lever from its axis
Moment Arm
Perpendicular distance
Stabilizing Force
Occurs when the force is too close to axis
Angular force
Movement force - Greatest when angle of pull is at the 90 degree point
Dislocating joint
Force is directed away from the joint - occurs past 90˚
How does patella promote mechanical advantage?
Patella changes vector force of quadriceps tendon, allowing knee to flex/extend
Stability
Occurs when all torques acting on an object are equal in force
COG
Center of Gravity
BOS
Base of Support
LOG
Line of Gravity
6 Principles of Stability
- The lower the COG, the more stable the object
- COG and LOG must remain within BOS for an object to remain stable
- Stability increases as BOS is widened
- The greater the mass, the greater the stability
- Greater friction between the supporting surface and BOS result in greater stability
- People have better balance when focusing on a stationary object
Components of Levers
Resistance, Axis, Force, Resistance Arm, Force Arm
Mechanical Advantage
MA = FA/RA, Ratio between the force arm and the resistance arm
1st Class Lever
Axis is between force and the resistance - Best for balance (either power or speed)
2nd Class Lever
Resistance in the middle with axis and force on opposite ends - Best for power - Initial Force Arm is far from axis
3rd Class Lever
Force in the middle of axis and resistance - Best for ROM; Most common lever in the body, built for range
Force Formula
F x Fa = R x Ra
determine force
F = R x Ra/Fa
Fa (Force Arm)
- Measures from insertion to axis
- Insertion farther from axis = power
- Insertion closer to axis = speed/range
