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Biomechanics
is an important aspect of trampolining for coaches.
But it's not a big bad scary thing after all.
Here are some of the basic terms:
| Centre of Mass |
The main point in the body which
is attracted towards the earth. This point however, need not lie within
the body, because it is always being altered when you move around. The
path which this point passes through throughout the skill, is called the
path of the centre of mass. Once this is set, it doesn't change. It will
need an external force to change it, (a push or pull of a coach). |
| Velocity |
Speed in a specified direction,
like 100mph downwards [headfirst] etc |
| Force |
a push or a pull, like pushing
off from the bed, stopping still etc |
| Eccentric force |
a force which doesn't necessarily
follow the path of the center of mass. |
| Momentum |
how much motion you've got, you
can work this out by Velocity x Mass. |
| Linear Momentum |
How much momentum you've got
going in a straight line, like in a straight jump. see above for a
definition of momentum. |
| Angular Momentum |
How much momentum you've got when
your somersaulting. |
| Moment of Inertia |
Imagine your in a really tight
tuck shape, (a rough circle shape), it is the diameter of the circle.
The tighter the tuck (smaller diameter), the smaller the moment of
inertia (you spin faster). |
| Radius of Gyration |
Imagine your in that really tight
tuck shape again, this time it is the radius of the circle, not the
diameter. |
| Law of conservation of momentum
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Once you start rotating, the
amount of momentum you have can't be altered. If you open out on a tuck
front, you still keep spinning. |
| Transfer of momentum |
When you land a back drop, you
have to transfer the momentum of going backwards, to going forwards to
make sure you stand up. |
| Newton's First Law |
"A body will remain at rest or
uniform motion [tuck front] unless acted upon by an external force". You
will keep rotating until you put your feet out, (or hit something!) |
| Newton's Second Law |
dont go there!!!! |
| Newton's Third Law |
For every action, there is an
equal and opposite reaction. Try doing a pike jump with no arms, you
can't help but bend over forwards. |
| Parabola |
A fancy word for flight path,
imagine a really badly travelled front somersault, think of the big
curvy flight path. |
To work out the
biomechanics of a skill
The easiest thing to do is go
through the skill and just look at what the gymnast
does at each point, (that is, at take-off, shaping and prep for landing) and
use
as many of the words from above as you can.
A tucked front somersault for example,
Take off
The gymnast creates Eccentric (Off-centre) Force whilst in contact with the
bed.
This is when the hips are slightly displaced backwards, they have to do
this, or else they will just go straight up and not rotate.
The parabola (flight path) is now set, it cannot be changed in flight
by the gymnast, the coach could though by catching, or nudging them out of
the way etc.
Shaping
Linear momentum, (straight up) changes to angular momentum (because you
are somersaulting). This makes the Moment of Inertia and Radius of Gyration
decrease. You will have more momentum, (you go around a bit faster).
Prep for landing
You open out...
This slows you down (reduces your velocity and momentum, increases your
Moment
of Inertia and Radius of Gyration, meaning you haven't conserved as much
momentum).
Angular Momentum returns to Linear Momentum, because you are back up
straight.
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