Biomechanics final exam UNH

kinematics

kinematics

description of motion considering space, time, patterns, speeds, movement sequence

are forces considered in kinematics?

no

kinetics

the study of the relationship between the forces acting on a system and the motion of the system

inertia

concept relating the difficulty with which an objects motion is altered

mass

the quantity of matter composing an object

units of mass

English: slug. SI: kg

mass

the measure of inertia for linear motion

mass

the property giving rise to gravitational attraction

centre of mass (centre of gravity)

point representing the average location of the mass of a body

position of centre of mass changes with changes in .... (2 words)

body configuration

motion of the centre of mass represents the (....1 word......) motion of the body as a whole

average

force

mechanical interaction between an object and its surroundings. the push or pull of one object on another.

is force a vector?

yes

name the vector quantities of force (3 total)

magnitude, direction, point of application

what are the 2 actions of forces

acceleration and deformation

T or F: it is often assumed that forces cause minimal deformation?

True

formula for force

F = mass (m) x a (acceleration of centre of mass)

1lb = how many newtons

1lb = 4.45N

net force

resultant force derived from the vector addition of two or more forces

what does net force reflect

all of the forces acting together

concentrated force

a force that is applied at a single point

distribution force

a force that is applied over a distributed area. can be approximated by a concentrated force that has same net effect

weight

the force due to gravity

formula for weight (Fw)

Fw = mass (m) x g (acceleration due to gravity - 9.81m/s^2)

weight always acts at the (....3 words.....), and points towards the (......4 words....)

centre of mass. centre of the earth

pressing or squeezing force directed normally (perpendicular) to a surface

compression. Fn arrow goes down

pulling or stretching force directed normally to a surface

tension. Fn arrow goes up

sliding or tearing force directed parallel to a surface

shear. Fs goes parallel along surface

T or F: compression, tension, and shear deform an object under load

True

formula for shear stress

σ = F / A.

σ = stress

F = force applied

A = area force is applied over

pressure

stress due to a compressive force

bending

asymmetric loading that produces tension on one side of a body, compression on the other

during bending, where are compressive and tensile stresses the greatest?

at the surface

torsion

load producing twisting of a body. creates shear stress.

during torsion, where are the shear stresses the greatest?

at the surface

linear motion (translation)

all parts of an object or system move the same distance in the same direction at the same time

linear kinetics

the kinetics of particles, objects, or systems undergoing linear motion

internal force

force applied to a system from within the force

external forces

forces applied to a system from outside the system

which forces (internal or external) are NOT included in mechanical analyses

internal

What are Newton's 3 laws of motion?

1. Law of Inertia

2. Law of Acceleration

3. Law of Action-Reaction

what is the law of inertia

a body will maintain a state of rest or constant velocity unless acted on by an external force

which newtons law states that if there is no net external force acting on the body, then the body will remain motionless

1st law: law of inertia

what is newtons 2nd law

law of acceleration

formula for law of acceleration

F = ma

F = net external force acting on a body

M = mass of the body

a = linear acceleration of the body centre of mass

if there is a net external force acting on a body: the acceleration of the body's centre of mass is:

• directly proportional to the net force

• inversely proportional to the body's mass

• in the direction of the net force

if net external force and velocity are in the same direction what happens to magnitude of velocity?

it increases

if net external force and velocity are in opposite directions what happens to magnitude of velocity?

magnitude of velocity decreases

if there is a larger net force, there will be what type of change in velocity? (2 words)

larger & faster

what happens to change in velocity if

V + F+ \n V + F- \n V- F- \n V- F+

increase in + direction \n decrease in + direction \n increase in - direction \n decrease in - direction

what can a net external force produce? (3 changes)

change in speed (magnitude of V)

change in direction

change in both speed and direction

if a vector is parallel...

= change in speed

if a vector is perpendicular...

= change in direction

what is newtons 3rd law?

law of reaction

law of reaction (3rd law)

For every action there is an equal and opposite reaction

contact forces

forces pushing against or pulling an object as the result of physical contact with another object

name the 2 contact forces within biomechanics

forces applied from outside the body

forces originating inside the body

non-contact forces

forces that do NOT results from direct physical contact

examples of non-contact forces

gravity, magnetic, electric

resistive

normal force resulting from pushing or pulling against a rigid body

friction

acts over area of contact between 2 surfaces, opposes sliding between surfaces

produced by spring-like objects; proportional to deformation. provide an example of this force. resistance changes depending on stretch.

elastic force. ex: resistance bands.

viscous

force produced by fluids. proportional to velocity. resistance doesn't change.

combines behaviour or a spring and a fluid. force depends on deformation, rate of deformation and time. provide an example of this type of force

viscoelastic force. biologic material (bones, tendon, muscle)

static friction

type of friction that applies when objects are not sliding relative to each other

kinetic friction

type of friction that applies hen objects are sliding relative to each other

what will happen to object if the Sum of other shear forces exceeds maximum static friction force

object will begin to slide!

direction of kinetic force is always (....opposite OR in same direction....) of sliding?

opposite

T or F: once object is moving, kinetic friction force doesn't change

true

what is elastic force produced by? what it is proportional to

produced by spring-like objects

proportional to deformation

what is viscous force produced by? what is it proportional to?

produced by fluids

proportional to velocity

does resistance increase or decrease if object length increases?

resistance increases

joint contact forces

compressive force resulting from bone-on-bone contact

musculotendon force

active and passive forces generated by a muscle-tendon unit

ligament force

passive force produced by stretching of a ligament

T or F: ligament force cannot produce, it can only resist force

true

intervertebral force

force acting on the disk between spinal vertebrae

resultant joint force

net force acting across a joint (due to all surfaces)

are musculotendon forces produced at the origin and insertion equal or different?

equal

what stretches more, tendon or ligament?

tendon

tendon forces can function to store energy during (....1 word....) contractions

eccentric

formula for stress

stress = F / A

do ligaments get more or less stiff when they are stretched

more stiff

which force curve is more exponential? ligament or tendon

ligaments

ligaments or tendons?

- prevent unwanted joint movement \n - provide mobility and stability

ligaments

intervertebral force: nucleus expands against (...1word...) when compressed

annulus

nucleus experience large (....type of stress...)

compressive

fibers of annulus experience large (...type of stress...)

tensile stress

3 primary joint forces (where in body)

bone, muscle, ligaments

angular motion (rotation)

All points in an object or system move in a circle about a single axis of rotation. All points move through the same angle in the same time

angular kinetics

the kinetics or particles, objects, or systems undergoing rotation

linear acceleration

what type of acceleration will result from a force applied though the centre of mass

what type of acceleration will result from a force applied at any other point than the centre of mass?

linear and angular acceleration

torque

the measure of extent to which a force will cause an object to rotate

line of action

the imaginary line that extends from the force vector in both directions

moment arm

shortest distance from a force's line of action to the axis of rotation

moment arm is always (...perpendicular OR parallel...) to the line of actions and passes (...through OR around...) the access of rotation

perpendicular

through

computing moment arm formula

moment arm = d sin theta

d = distance from axis of rotation where force is applied

theta: angle where force is applied

3 components of torque

magnitude, direction (+ or -), and specific axis of rotation

torque formula

forces magnitude (f) x moment arm (d⊥)