Transcript Coach Grade 1 - Brentwood Trampoline Club

Club Coach
Mechanics
© Tony Fagelman 2006
Take-Off
• Time is a major factor
• Take-off is the most
important part of any
skill
• Without a good takeoff, the skill cannot be
performed correctly
© Tony Fagelman 2006
Flight
• This is 2nd part of any
movement using the
trampoline
• The flight requires
control and phasing
© Tony Fagelman 2006
Landing
• Safety is a major
factor
• Performer must be
in control
• Preparation for next
skill
© Tony Fagelman 2006
Newton’s Laws of Motion
• 1st Law :
– A body will continue in its uniform state of motion or
rest unless acted on by an external force.
• 2nd Law:
– The rate of change of momentum is proportional to
the force causing it and the change takes place in the
direction in which the force acts.
force = mass x acceleration
– if mass is constant, acceleration is proportional to the
applied force
• 3rd Law:
– For every action there is an equal and opposite
reaction
© Tony Fagelman 2006
Centre of Mass
• The point though which the line of force of
“attraction to the earth” takes place.
Centre of Mass
© Tony Fagelman 2006
Forces
• Push & Pull
– A force is needed to:
•
•
•
•
Start a motion
Change the rate of motion
Change the direction of motion
Cause motion to stop
© Tony Fagelman 2006
TORQUE
• The Rotational push or pull
• Caused by a FORCE
• Eccentric or Off-Centre Force also
called Torque
– This will always create rotation
– A torque whose line of action does not
pass through the centre of mass of the
body on which it acts
© Tony Fagelman 2006
Displacement of COM
• What happens when we displace the Centre
of Mass outside the body?
Centre
of
Mass
© Tony Fagelman 2006
Linear Movement
• Movement in a straight line
• Remember Newtons’ 1st
law
– A body will carry on unless
acted on
• A trampolinist will bounce
upwards until gravity pulls
them back down again
© Tony Fagelman 2006
Angular Movement
• An off-centre force acting
around the Centre of Mass
will create angular movement
(Somersault rotation)
(Remember displacement of COM)
• Rotation around an axis
• Somersaulting demonstrates
both Linear Movement and
Angular Movement
© Tony Fagelman 2006
Axis of rotation
• somersault axis
• twisting axis
• side somersault axis
Any rotation can be
described using the 3
axis.
© Tony Fagelman 2006
Inertia
• The resistance of a body to change
• Inertia is measured by Mass
• Or Not… as the case may be
© Tony Fagelman 2006
Momentum
• Is the amount of Linear
Movement “energy” in a
body as it moves
• It is the “quantity” of motion
– Velocity x Mass
© Tony Fagelman 2006
Speed
• Is the rate of movement
of the Centre of Mass
© Tony Fagelman 2006
Conservation of Linear Momentum
• Conservation & Creation
– Whatever you put into a closed system is
what you have.
• Remember Newton’s 1st Law
• Can a performer do anything to help themselves to
safety if they do not have sufficient somersault
rotation?
© Tony Fagelman 2006
Changing Linear Momentum
• All changes in Linear
momentum are
caused by external
forces.
• The changes are
determined by the
size and direction of
the force
© Tony Fagelman 2006
Projectile Motion
• when a performer is in
flight he/she is a projectile
• the only force acting on
them is the force of gravity
• the flight path is
predetermined and will not
change once in flight.
• the CoM will follow a
parabolic flight path
© Tony Fagelman 2006
Moment of Inertia
• The measure of the
body’s reluctance to
start rotating (or
change direction)
around an axis
© Tony Fagelman 2006
Angular Speed
• The rate of rotation
around an axis
• To control angular
speed in flight (by
changing the moment
of inertia), the body
can change shape
© Tony Fagelman 2006
Angular Momentum
• The amount of
rotational energy in a
body as it rotates
around an axis
© Tony Fagelman 2006
Changing Angular Momentum
• These are caused by external torques.
• The changes are determined by the size
and direction of the torque
© Tony Fagelman 2006
Conservation of Angular
Momentum
• Angular momentum
will remain the same
until changed by an
external torque
– Tucking when
somersaulting
– Straightening when
somersaulting
© Tony Fagelman 2006
Mechanics of somersaulting
• Creation of a
somersault
• Angular movement is
caused by TORQUE
• Torque = Force x
Perpendicular
distance from axis of
rotation
© Tony Fagelman 2006
Early Twist
• Twist is initiated from the bed
Arms are
set whilst in
contact
with the
bed.
Movement
is initiated
© Tony Fagelman 2006
Trampolinist
has left the
bed
Arms are
brought
together to
allow twist to
continue
Late Twist
• The Twist is initiated
in the air
– There are a number of
theories given to this
action.
© Tony Fagelman 2006
Tilt Twist
• By moving the body
outside the line, twist
can be initiated
• The greater the tilt,
the greater the twist
© Tony Fagelman 2006
Asymmetrical arm twisting
• By moving the arms
asymmetrically, twist
can be generated
• The greater the arm
movement, the larger
the twist
© Tony Fagelman 2006