L4 - Linear Kinematics

Kinematics

the branch of mechanics that describe the spatial and temporal components of motion

Kinematic analysis can be either qualitative or quantitative

True

Qualitative kinematics

• non-numerical

• subjective

• cost-effective

Quantitative kinematics

• analyzed numerically

• more precise

Translational kinematics

linear motion that occurs in a straight line

Curvilinear kinematics

linear motion that occurs in a curved path

Optical motion capture

markers on the body are tracked by a camera sensor that scans signals from either an active (diodes that emit infrared light) or passive (retroreflective) marker system

Electromagnetic motion capture

• sensory placed on body are used to measure low frequency magnetic fields generated by a transmitter force

• a magnetometer within each sensory gives position and orientation of each sensor

Accelerometers

• measure the acceleration of specific body segments

• integral calculus used to find velocity and displacement data

• can measure accelerations in one direction (uniaxial) or three orthogonal direction (triaxial)

Points of interest for collecting kinematic data are identified with respect to the origin in three dimensions

True

The origin of points of interest is always your zero point in the reference system and will always be in the middle

False, will not always be in the middle

Reference systems have to be oriented in a specific manner

False, may depend on surrounding environment

Reference systems may be reoriented such that one axis (y) runs along the long axis of a segment and the other axis (x) is perpendicular to the y-axis

True

Local reference system

• as segment moves, the coordinate system also moves

• allows for the identification of a point on the body relative to an actual body segment rather than to an external point

Global axis

fixed reference for entire structure (body)

Local axis

reference to individual object that moves with that object (arm)

Kinematics change over time

True

Scalars

• quantities that can be described fully by their amount

• mass, distance, volume, speed, temperature

Vectors

• quantities descriver by both magnitude and direction

• velocity, acceleration, displacement

Multiplying a scalar by a vector changes its direction but not magnitude

False, changes its magnitude but not its direction

Distance

measure of the path travelled (magnitude) in meters

Displacement

measure of the distance between the two points (magnitude and direction) in meters

Speed

rate of change in linear distance (scalar)

Velocity

rate of change in linear displacement (vector)

What does a position/time graph show

shows the change in horizontal position as a function of time

Describe what the following indicates on a position/time graph: steep slope

position is changing rapidly = greater velocity

Describe what the following indicates on a position/time graph: slope zero

object not changing position = velocity is zero

Describe what the following indicates on a position/time graph: positive slope

increasing velocity

Describe what the following indicates on a position/time graph: negative slope

decreasing velocity

First central difference method

uses the difference in positions over two frames as the numerator and uses two time intervals in the denominator

Shorter time periods make for more accurate velocity calculations

True

First central difference method calculates what type of velocity

average

Instantaneous velocity

velocity at a specific time found by using the shortest time period possible

Describe what the following indicates on a position/velocity graph: local extremum (slope changes)

velocity zero

The velocity of a body is rarely constant in human motion

True

Describe what the following indicates on a velocity/acceleration graph: positive slope

positive acceleration

Describe what the following indicates on a velocity/acceleration graph: negative slope

negative acceleration

Describe what the following indicates on a velocity/acceleration graph: velocity and acceleration are the same sign (both positive or both negative)

object is speeding up

Describe what the following indicates on a velocity/acceleration graph: velocity and acceleration are different signs (one positive and one negative)

object is slowing down

If an object is moving in the positive direction what will their displacement be

positive

If an object is moving in the positive direction what will their velocity be

positive

If an object is moving in the negative direction what will their displacement be

negative

If an object is moving in the negative direction what will their velocity be

negative

If an object is moving in the positive direction with a positive acceleration what will their velocity be

increasing

If an object is moving in the positive direction with a negative acceleration what will their velocity be

decreasing

If an object is moving in the negative direction with a positive acceleration what will their velocity be

decrease

If an object is moving in the negative direction with a negative acceleration what will their velocity be

increase

How do you increase running speed

• increase stride length

• increase stride rate

• increase both

Impaired populations restrict their gait to increase caution while walking. What restrictions are done

• slower cadence (steps/min)

• increased support phase of cycle

• decreased swing phase of cycle

• shortening step length

What factors influence projectiles

• projection angle

• projection velocity

• projection height

Projection angle has the largest impact on distance an object travels in projectile motion

False, projection velocity