We are always rotating with an axis of waist in the air
[Summary]
There are some remarks which advice you to rotate with an axis of chest to get a higher flip.
However, we cannot determine an axis of rotation in the air.
The axis of the rotation in the air is always CG (center of the gravity) of your body and it’s almost always around the waist.
Sometimes you see a rotation with an axis of chest because the actual axis(CG) is moving.
In the case where a body(CG) goes upward, you see rotation with an axis of chest.
He looks rotating with the axis of chest.
You can see his waist is rotating around his chest(However, the actual axis is his chest).
He looks rotating with an axis of waist.
You can see his chest and legs rotating around his waist.
It is not that since we rotate with the axis of chest, we can get higher backflips, but that since we get higher backflips, we look as if rotate with the axis of chest.
This is very similar to Tip 4 : Tuck fast without thinking(bringing chest to knees is the same as knees to chest ) in a regard of that prevailing tip is the result of a good back flip and it’s not either the cause or tip.
However, I think there are some people who needs the imagination of the axis of chest to jump more upward.
[Details and Theory]
– How does another part looks to be the axis of rotation? –
If our body rotated with the axis of chest, CG around our waists would rotate around our chests.
The track of CG would be looked bizarre.
In the air only gravity is applied to the body, so CG must do parabolic motion.
Since backflip contains rotation with the axis of CG and the movement of CG of its own, we sometimes see it as if rotate with another axis.The apparent axis is the part which doesn’t move mostly in the whole rotating object.
How does that part exist in spite of rotation.
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– In the particular part, whole body movement and rotation cancel out –
It exists due to offsetting by the upward movement of the whole body and the downward movement of the rotation in particular part of the rotating object.
Assume that you are on a gondola of a ferris wheel.
The ferris wheel rotates and then your gondola moves from ① to ②.
The axis of this rotation is the center of the ferris wheel.
Let’s assume while the gondola is moving from ① to ②, whole ferris wheel is moving upper right.
In this case, the downward movement of your gondola (by rotation) and the upward movement of the whole ferris wheel offset each other.
It is true that the gondolas rotate with the axis of the center of the ferris wheel, but it looks as if your gondola is the axis of rotation for your gondola doesn’t move.
In this example, we can see the center of the ferris wheel as CG, your gondola as apparent axis like chest or some another part.
Chest goes down faster than waist since the distance from the axis of rotation(CG) is longer.
That chest looks like the axis of rotation implies that whole body goes up as fast as it offsets chest’s fast downward movement by rotation.
Apparent axis shifts as time goes is related to this content.
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