Kin 372 Final Decoux

Circular motion

describes the linear motion of any point on the radius.

speed

rate of distance traveled how fast an object moves

Linear Kinematics

THE BRANCH OF DYNAMICS CONCERNED WITH THE DESCRIPTION OF LINEAR MOTION

1. Space 2. Time

for motion to occur, two things are necessary..

F=MxA (N)

force equation

external forces

forces that act on an object as a result of its interaction with the environment surrounding it Example- weight (load) of an object

internal forces

forces that act within the object or system whose motion is being investigated. Example- Force generate by muscles

contact force

forces that occur between objects in contact with each other.

Noncontact forces

forces that occur even if the objects are not touching each other.

mixed motion

general motion is also called

postition

linear location of object of interest at a given instant

stabilizing or dislocating

parallel component can be either

angular momentum

quantity of angular motion possessed by a body Measured as the product of moment of inertia and angular velocity

Velocity

rate of change in position in a specific direction rate of displacement

acceleration (as a vector)

rate of change in velocity change in velocity / change in time (vector)

2nd class lever

resistance is between axis and force resistance and force are opposite directions Most levers used in daily life

angular inertia

resistance to change in angular motion

circular motion

special form of curvilinear motion

Displacement

straight-line distance in a specific direction from initial (starting) position to final (ending) position

rectilinear motion

straight-line translation No change in direction or orientation

Motion

the act or process of changing place or position with respect to some reference object

Friction

the force acting over the area of contact between two surfaces in the direction opposite that of motion or motion tendency.

Momentum

the product of an object's mass and its linear velocity

Biomechanics

the study of the structure and function of biological systems by means of the methods of mechanics

-Linear motion (AKA translatory motion) -Angular motion (AKA rotary motion)

two classifications of movement patterns:

-Rectilinear motion -Curvilinear motion

two types of linear motion

Net force

vector sum of all the external forces acting on an object

some form of force

what is the cause of motion

Kinetics

-study of the action of forces -CAUSE of motion

Kinematics

-the form, pattern, or sequencing of movement with respect to time -DESCRIPTION of motion

-balanced movements when axis is in the middle -force generation when the axis is near the resistance -speed and range of motion when the axis is near the applied force

1st class levers are effective for

Ex- wheelbarrow -Human motion example: Gastrocnemius raising the body up onto the toes during standing calf raise

2nd class lever example

-Force generation because the mechanical advantage is always greater than 1 -Large resistance can be moved with relatively small applied force

2nd class levers are effective for

Human motion example: Biceps brachii at the elbow during lifting phase of curl exercise

3rd class lever example

-Speed and range of motion but not force generation because the mechanical advantage is always less than 1 -Requires large force to move a relatively small resistance

3rd class levers are effective for

Newton's First Law (inertia)

A body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state.

-torque -Change in point of force application -Change in direction of force line of action

A change in moment arm causes change

the distribution of mass with respect to the axis of rotation.

A factor that influences angular momentum is

Newton's Second Law (acceleration)

A force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body's mass.

1st class lever

Axis located between resistance and force resistance and force in same direction mechanical advantage depends on the location of fulcrum

Torque

A muscle controls or creates a movement through the development of

smaller

A muscle with a short moment arm generates a_________ moment than a muscle with a longer moment arm that generates the same contraction force.

Force

A push or a pull

lever

A simple machine with bar-like body that rotates about an axis

Newton's Law of Gravitation

All bodies are attracted to one another with a force which is proportional to the product of their masses (m), and inversely proportional to the square of the distance (d) between them.

Pulley

Changes the direction of an applied force

active insufficiency

Condition occurring when a two-joint muscle cannot shorten enough to cause full range of motion at both joints it crosses at the same time

kinetic friction

Constant-magnitude friction generated between two surfaces in contact during motion

the sliding of the actin chains on the myosin chains.

Contraction of skeletal muscle results from

center of gravity

Moment of Inertia of an object about an axis through the

Counterclockwise → + Clockwise → -

Direction of torque is defined as follows:

Distance between the muscle's anatomical attachment to bone and the axis of rotation at the joint center, angle of muscles attachment to bone

Factors that Affect a Muscle's Moment Arm

The length and arrangement of the fibers composing the muscles The length of the muscle's moment arm

Factors that Influence a Muscle's Ability to Produce Joint Motion

Newton's third law (reaction)

For every action, there is an equal and opposite reaction. When one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and opposite in direction on the first body

3rd class levers

Force is between axis and resistance Force and resistance are in opposite directions Majority of the human body joints (95+%) Source of human mobility

force x force arm =

Force torque =

static friction

Frictional force that develops between two surfaces in contact that are not moving relative to each other.

atlanto-occipital joint

Human motion example of 1st class lever

passive insufficiency

Inability of a two-joint muscle to stretch enough to allow full range of motion at both joints at the same time.

the muscle torque and the resistive torque.

Net torque is the vector sum of

circular motion

Object moves along the circumference of a circle Moves in a curved path of constant radius.

angular motion

Occurs when all points on a body or object move in circles (or parts of circles) about the same fixed central line or axis

linear motion

Occurs when all points on a body or object move the same distance, in the same direction, and at the same time

acceleration (as scalar)

Rate of change in speed change in speed / change in time (scalar)

linear inertia

Resistance to change in linear motion Quantified by an object's mass

resistance x resistance arm

Resistance torque =

Resultant force

Result of vector addition of two or more forces

net joint torque

Sometimes called resultant joint torque Sum of the torques produced by the muscles about the joint Agonist vs. antagonist torque

general motion

The combination of linear and angular motion is called

parallel component

The component acting parallel to the attached bone does not produce torque

rotary component

The component of muscular force that produces torque at the joint crossed, is directed perpendicular to the attached bone.

unbalanced force acts on the object to keep it in a circle. If force stops acting on the object, it will move in a linear path tangent to the its direction of movement when released.

The logic explaining circular motion relates to the fact that an

concurrent forces

Two or more forces whose lines of action intersect at a single point. When forces do not act along the same line the resultant force can be found best by trigonometric means.

direction of any resulting movement.

The net torque at a joint determines

Torque

The product of force and moment arm

moment of inertia

The quantity that describes angular inertia is called

injury rehabilitation, injury prevention, & performance enhancement

Three main goals & application areas within biomechanics

magnitude and direction

To fully describe a force, you must describe its

-Also called moment of force or moment -The turning effect produced by a force -Can be thought of as an angular or rotary force -Caused by an eccentric force -Eccentric force is NOT the same as eccentric contraction. An eccentric force is a force applied at a distance away from an axis of rotation -Cause of angular motion

Torque

T = F x d⟂ force x moment arm

Torque formula

collinear forces

Two or more forces that have the same line of action (but not necessarily the same direction along this common line of action). When forces act along the same line, the resultant force can be found by algebraic means and well as graphical means.

mass x gravity

Weight =

The perpendicular distance between a force's line of action and the axis of rotation

What is moment arm (d⟂)?

Whenever gravity is the only acting external force, angular momentum is conserved.

What is the principle of conservation of angular momentum?

angular impulse

What produces change in angular momentum?

unifrom acceleration

When the acceleration of an object is constant Occurs when the net external force acting on an object is constant and unchanging

Distnace

a measure of the length of the path followed by the object whose motion is being described, from its starting (initial) position to its ending (final) position

1) the object's mass 2) how the mass is distributed relative to the axis of rotation

angular inertia is dependent on two variables:

within the body (ex.- somersault) or an axis outside of the body (ex.-high bar swing)

angular motion can occur

Sarcomere

basic functional unit of muscle fiber

Curvilinear motion

curved translation Direction of motion is constantly changing but no change in orientation

angular motion

describes the rotational motion of the entire radius.

radius of gyration

distance from the axis of rotation to a point where the body's mass could be concentrated without altering its rotational characteristics