Biomechanics 2 Flashcards
Definition of angular motion
movement of a body or part of a body in circular path about an axis of rotation
Definition of eccentric force
force applied outside centre of mass resulting in angular motion
Definition of torque
measure of turning force applied to body
What is linear motion created by
- direct force
- external force passes through the centre of mass
Name a sporting example in linear motion
skeleton bob at top speed
What is angular motion created by
- eccentric force
- external force passes outside the centre of mass
Name a sporting example in angular motion
- gymnastics somersault
- drive and recovery leg rotating about the hip joint of a runner
- arm rotating about the shoulder joint of a tennis player serving
What is principal axis of rotation
imaginary line that passes through centre of mass about which a body rotates:
longitudinal, transverse and frontal axis
Name the 3 axis’ of rotation
- longitudinal
- transverse
- frontal
What is the longitudinal axis
-runs from head to toe through the centre of mass
What is the transverse axis
from left to right through the centre of mass
What is the frontal axis
runs from back to front through center of mass (cartwheel)
Name the 3 descriptors important to angular motion
- angular velocity
- moment of inertia
- angular momentum
What is angular velocity
rate of velocity at which an object is rotating around a center or a specific point
Give the equation for angular velocity
angular displacement / time taken
What is angular velocity measured in
rad/s
What is moment of inertia
resistance of body to change its state of angular motion/ rotation.
Give the equation for moment of inertia
sum of (mass x distribution of mass from axis of rotation)
What is moment of inertia measured in
kgm2
Name 2 factors that effect moment of inertia
- mass
- distribution of mass from the axis of rotation
Why are complex twists typically performed by athletes with a low mass
- low mass decreases moment of inertia & resistance to change state of rotation
- so athletes can start rotation, change rate of rotation and stop rotation with ease
How does mass affect moment of inertia
- greater the mass the greater moment of inertia
- lower the mass the lower the moment of inertia
How does distribution of mass from the axis of rotation affect moment of inertia
- further the mass moves from the axis of rotation, greater the moment of inertia
- closer the mass moves from the axis of rotation, lower the moment of inertia
How does close ‘tucked’ mass distribution affect moment of inertia
decreases moment of inertia and the resistance to change state of rotation