Biomechanics Pt. 3 (9/5d) Flashcards Preview

PT605 > Biomechanics Pt. 3 (9/5d) > Flashcards

Flashcards in Biomechanics Pt. 3 (9/5d) Deck (17)
Loading flashcards...

For every force, there is an ___ and ___ force

equal and opposite


Vector Composition

Adding forces

Vector L + Vector M = Vector R (resultant vector)

Direction of forces are important, pay attention to +/-


Vector Reduction

Subtracting forces

A single resultant vector can be “resolved” into separate component vectors

Force F can be broken into its two components: FH & FY


Static rotary equilibrium

Internal torque = external torque

The net torque is equal to zero → the joint is not moving


3 Types of Musculoskeletal Levers

First class (very few)
Second class (almost none)
Third class (most common)


Why do muscles have small moment arms?

so they can move external forces over large distances quickly (force-distance tradeoff)


Force-Distance Tradeoff

big force=large distance
small force =short distance


Newton's 1st Law

Law of Inertia - amount of force required to alter the velocity of a body


Static equilibrium

linear or rotational velocity is 0


Dynamic equilibrium

linear or rotational velocity is constant


Mass of a body

describes its inherent resistance to a change in linear velocity


Mass moment of inertia

describes the body’s inherent resistance to a change in angular velocity

indicated by I, expressed in units of kilograms per meter squared (kg∙m2)

Depends on the 1) amount of mass of a body and 2) distribution of mass of a body


Newton's 2nd Law

Law of Acceleration - force equals mass times acceleration

Refer to notes for Linear Force and Rotary Torque Acceleration relationships


Newton's 3rd Law

Law of Reaction - anytime a force is exerted on an object, the object exerts an equal but opposite force on the object

EX: Joint reaction forces, Ground reaction forces


Joint reaction forces

force that is created in response to a muscle pulling one bone against the other during activation

The joint reaction force is always opposite the muscle force

Can compress or pull apart


Ground reaction forces

“I hit the ground, the ground hits me back”


Force has to be acting in what manner to contribute to torque?

1) acting at a distance
2) not parallel
3) not through the axis