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
When running what is the recovery leg’s moment of inertia and why
recovery legs mass is distributed close to axis of rotation at hip so moment of inertia is low
-resistance to rotation is low and leg moves back to ground quickly
When running what is the drive leg’s moment of inertia and why
drive legs mass is distributed far from axis of rotation at hip so moment of inertia is high
-resistance to rotation is high and leg moves slowly
How does moment of inertia effect angular velocity
-when moment of inertia is high
- when moment of inertia is high- resistance to rotation is also high
- so angular velocity is low and so rate of spin is slow
How does moment of inertia effect angular velocity
-when moment of inertia is low
- when moment of inertia is low- resistance to rotation is also low
- so angular velocity is high and so rate of spin is fast
What is angular momentum
quantity of angular motion possessed by a body
Give the formula for angular momentum
moment of inertia x angular velocity
What is angular momentum measured in
Kgm2rad/s
What is the conservation of angular momentum
angular momentum is a conserved quantity which remains constant unless an external force or torque is applied
How do you rotate around an axis
- angular momentum must be generated
- preparation phase: eccentric force or torque must be applied
What is linear motion
movement of body in straught or curved line where all parts move same distance, in same direction over same time
What is direct force
force applied through centre of mass resulting in linear motion
What is distance and what is it measured in
total length covered from start to finish
-measured in metres (m)
What is displacement and what is it measured in
shortest straight line rout from start to finish
-measured in metres (m)
What is speed, what is it measured in, formula
rate of change in distance
-measured : (m/s) (s) (m)
speed = distance / time taken
What is velocity, what is it measured in, formula
rate of change in displacement
-measured: (m/s) (s) (m)
velocity = displacement / time taken
What is acceleration, what is it measured in, formula
rate of change in velocity
-measured: (m/s/s) (m/s) (s)
acceleration = (final velcocity - initial velocity) / time taken
