biomechanics exam2

What is the influence of a longer moment arm on joint torques?

The longer the moment arm is the more load will be applied to the joint axis through leverage.

Angular distance

Total of all angular changes during its path of motion

What happens to the object when it is released?

When the ball is released, there is no longer radial acceleration, so the ball follows the tangential path

define mechanical stability

ability to maintain vertical projection of CG within base of support

why is timing of the throw important

because once the ball is released we can not control where the ball goes, therefore if it is timed wrong the ball will not go where you want it too.

compare concentric and eccentric muscle actions

concentric:Muscle internal moment & motion same direction Eccentric: Muscle internal moment & motion opposite direction

how do you increase stability of human balance?

get low and widen your legs

What are the components of a torque?

has an axis of rotation meaning one side is fixed in space moment arm and lever arm

a. Provide an example of how center of mass can be manipulated by changing body shape, and how this might be advantageous in sport.

if you go lower and have a wider stance you center of mass is now lower and this makes it harder to knock you over in a sporting match.

define Angular inertia

is the property of an object to resist changes in its angular motion

conservation of angular momentum

k or radius of gyration can easily be changed in order to conserve angular momentum.

Define the rotary components of a muscle force

perpendicular to bone segment, creates internal moment, and causes motion

Define non-rotary components of a muscle force

perpendicular to rotary component and parallel to bone, does not contribute to internal moment, and causes joint compression or distraction.

what factors affect angular inertia?

radius and mass

What are the effects of a torque?

rotation about an axis

Tangential acceleration

the acceleration directed perpendicular to the radius

Radial acceleration

the acceleration directed towards the center of rotation

Provide a scenario of when a longer moment arm would be advantageous

unscrewing a bolt with your hands vs unscrewing a bolt with a wrench.. the wrench provides a larger moment arm and thus more torque.

1) Describe the relationship between the radius of rotation and linear displacement of a point along the radius.

↑ radius of rotation = ↑ linear displacement

Angular velocity

(W) -Rate of change of angular displacement per unit of time -Direction depends on rotational direction

Angular acceleration

(a) Rate of change in angular velocity

how does radius of gyration influence inertia

- The closer the mass is distributed to the axis of rotation the easier it is to rotate but harder to transfer momentum

1st class lever

-Axis between the motive force and resistive force (MAR) -Examples in body Agonist/Antagonist action Elbow extension Plantar flexion cervical extension

Describe three units of measurement for angular position.

-Degrees (°) Most common -Revolutions or Rotations 1 revolution = 360° Qualitative analysis -Radian 1 radian = 57.3° Most appropriate

Radius of Gyration (k)

-Distance mass is distributed from a specific axis of rotation -Point where mass can conceptually be concentrated such that it does not alter the moment of inertia (I)

define angular momentum

-momentum is the angular analog of linear momentum -Quantifies the angular motion of an object -Product of body's rotational inertia and rotational velocity about an axis

Where do we observe torques in humans

1) all muscles produce torque about the joints they cross

What is a torque?

A torque is a turning affect produced by a force. It is directly proportional to the magnitude of force as well as the distance between the line of action of the force and the axis of rotation

What do the letters in A-R-M stand for?

A- Axis M-Motive force R- Resistive force

biomechanical stability

Ability of a loaded structure to maintain static equilibrium even at small fluctuations around the equilibrium position

Angular Speed

Angular distance traveled per unit of time

What limitations exist with regards to segmental calculations of center of mass?

Based on Caucasian male cadavers Completed in the 1930-40s Based on segments being "truncated cones

What is the major advantage of using radians to describe angular position?

Because it can easily describe motions beyond 360 degrees (a limitation of degrees) and converts easily to linear

2nd class lever

Resistance in middle (ARM) Torque advantage usually exists for motive force Not as versatile as 1st class lever e.g - Push-up

clinical stability

Response of a joint to an injurious perturbation

What force keeps an object like a baseball or a hammer throw along a curved path?

Restraining force is what causes the centripetal acceleration, to keep the ball rotating

what would happen if a racket or stick was shorter/longer when playing tennis or hockey?

Shorter- linear velocity would be slower longer- linear velocity would be faster

compare a moment arm to a lever arm

-Moment arm: Perpendicular distance between line of action of force and axis of rotation. Perpendicular to forces line of action and axis of rotation. -Lever arm: Distance between the point of force application (perpendicular component) and the axis of rotation

3rd class lever

-Motive force in middle (AMR) -Most joint complexes act as 3rd class levers -Muscle is motive force -Advantage in ROM and speed of movement but disadvantage in force example) knee extension

Explain equlibrium

-State characterized by balanced forces and torques No net forces and torques -Static Equilibrium When a body is completely motionless

3 conditions for having static equilibrium

-Sum of all horizontal forces (or force components) acting on body must be 0 -Sum of all vertical forces (or force components) acting on body must be 0 -Sum of all torques must be 0

provide specific ways that mechanical stability can be increased

1)Increased mass. 2)Increased Friction between body and surface. 3)Increased size of the base of support 4)Positioning the C of G as low as possible in vertical direction. 5)Positioning the C of G close to edge of the base of support in horizontal direction opposite to the direction of the oncoming external force.

What are three required pieces of information necessary to derive linear motion from angular motion?

1)Where is the axis of rotation? 2)What is the radius (distance from axis to the point you are interested in) 3)What are the angular kinematics IN RADIANS!!!!!

What are 3 different methods to determine center of mass?

1. Balance Method The weight (force of gravity) and vertical reaction force at the fulcrum (axis) must lie in the same plane.2. Suspension Method Same principle as balance method but easier to accomplish 3. MRI Reconstruction

Angular displacements

Difference between the initial and final positions of a rotating object

How do athletes on a curve (runners, cyclists, skaters etc.) turn? What is the source of radial acceleration?

In order to turn, you must change the direction of the velocity, which results in radial accelerations

The moment/torque created by a muscle is dependent on what 3 things?

Muscle force (F) Lever arm (d) angle of pull (0)

what is the center of mass?

Point around which mass or weight is considered to be concentrated "Balance point of the body "

center of mass (COM)

Point where gravitational force is applied "balance point"

what is a radian?

Ratio of the arc length (r) of a circle to the radius length Radians= arc length/radius

define Mechanical advantage

Ratio of the lever arm of the motive force to the lever arm of the resistive force for a given lever Mechanical advantage = Lever arm motive/ lever arm resistive