Mechanics of Human Movement Unit 1

What is biomechanics?

• the application of mechanical principles in the study of living organisms

• Examining the forces acting on (external) and within (internal) a body and the effects of these forces

• We look at rigid body mechanics, deformable body mechanics, fluid mechanics

Mechanics

• branch of physics that analyzes the action of forces and particles of mechanical systems

Rigid body

• a system of particles (i.e. body) which does not deform

Rigid Body Mechanics

• application of mechanical principles to a rigid body or system of rigid bodies

Statics

• the study of rigid bodies or systems that are in a state of constant motion (at rest or moving at a constant speed)

Dynamics

• the study of rigid bodies or systems that are subject to acceleration

Kinematics

• the what

• description of motion as a function of space and time without reference to forces causing motion

Kinetics

• the HOW

• relationship between forces acting on a rigid body or system and the motion of that rigid body or system

Deformable body

• A body that changes its shape and/or volume when acted upon by a force

Deformable body mechanics

• application of the principles of mechanics to a deformable body

Elasticity

• the propensity of a material to return to its original shape when deformed

Plasticity

• propensity of material to undergo permanent deformation when loaded

Viscoelasticity

• material exhibits both viscous and elastic characteristics when deformed (i.e. dependent on loading rate)

Fluid Mechanics

• application of the principles of mechanics to fluids (liquids and or gases)

Linear motion

• motion along a line with all parts of the body moving the same distance in the same direction at the same time

Rectilinear

• linear motion along a straight line

Curvilinear

• linear motion along a curved line

Angular motion (rotation)

• All parts of the body move in a circle about a central line or point (axis of rotation)

• all points move through the same angle in the same time

Axis of rotation

• imaginary axis the object is spinning about, perpendicular to the plane of motion

What is each branch of biomechanics broken into?

• Rigid body

  • statics and dynamics ——→ kinematics and kinetics

• Deformable body mechanics

  • elasticity, plasticity, viscoelasticity

• Fluid mechanics

  • liquids and gases

Linar kinematics

• is the kinematics of particles, objects, or systems undergoing linear motion

  • for us it can be objects (basketball) or the person (the player)

Vector

• a quantity that has both magnitude and direction

  • magnitude is the size of the vector (length)

  • direction is the orientation of the vector

Distance

• length of a path

• scalar

Displacement

• vector

• difference between initial and final positions; independent of path

Motor efficiency

• the ratio of the magnitude of displacement to the distance traveled is an indicator of movement efficiency

  • smaller ratio = less efficient

  • larger ratio = more efficient

• Displacement/distance

  • unitless answer

Can you have a movement efficiency greater than 1?

• NO

Linear velocity

• describes the rate of change of linear or angular position with respect to time

Instantaneous velocity

• specifies how fast and in what direction one is moving at one particular point in time

• magnitude of instantaneous velocity is exactly the same as instantaneous speed

Linar acceleration

• the rate of change of linear or angular velocity with respect to time

(+) initial velocity (+) acceleration

• increase in (+) direction

• speed up

• propulsive

(+) initial velocity (-) acceleration

• decrease in (+) direction

• slow down

• braking

(-) initial velocity (-) acceleration

• increase in (-) direction

• speed up

• propulsive

(-) initial velocity (+) acceleration

• decrease in (-) direction

• slow down

• braking

when is acceleration propulsive?

• acceleration is propulsive if the magnitude of velocity increases

  • object “speeds up” or “accelerates”

When is acceleration braking?

• acceleration is braking if the magnitude of velocity decreases

  • object “slows down” or “decelerates”

An object with no acceleration is…..

• moving with a constant velocity

General Motion

• a combination of translation and rotation