Angle of Incidence:
Before the angle of
incidence is gone into detail it must be made aware that when a ball makes
contact with an object (bat, ground, wall or body part) it doesn’t lose energy,
the energy is converted into other forms (Blazevich, 2010). “Coefficient of
restitution
describes the proportion of total energy that remains with the object after
collision (Blazevich, 2010, p. 117)” This energy that remains determines how
high the ball is to bounce after contact, after contact with the forearms the
volleyball will rebound quicker if the platform of the forearms is smoother (Hede, Russell & Weatherby, 2011). The smoother and more
locked the elbows and wrists are the more accurate the ball is at being
performed at the correct angle (Hede et. al., 2011). The angle of reflection is
greater than the angle of incidence which is the flight of the ball when it
comes over the net (Blazevich, 2010). Meaning that for the ball to go in the
air (the dig stopping the ball hitting the ground and preparing for a set)
(Keeling, 2007) the ball must be hit from directly underneath the 90 degree
angle is best as mentioned earlier.
Kinetic Chain – Push-like motion:
Image 2: Visual imagery for kinetic chain of the volleyball dig. Source Unknown
Video 1:
Natalie Schmitting demonstrating a volleyball dig using the push-like motion. (About.com,
2012).
The kinetic chain is also referred to as the summation of forces, which our
body can produce if the joints and next movement from the body is performed at
the right time. This is where the volleyball dig can differ in technique; the ‘correct
technique’ uses a push-like motion which is portrayed in image 2. The figure is
using their legs for the strength, and moving the shoulders at the last bit
just before contact with the ball to achieve the correct angle. This motion
uses all parts of the body to achieve the most power in the dig as can be seen
in video 1 above where Natalie’s body extends at the same time. The other technique is where the arms are used
as levers as their axis of rotation
is that of the shoulders (Blazevich, 2010). This technique only gets power from
that of the rotational point of the shoulders whereas the push-like motion from
Natalie gets power from the proximal joints in her dig.
Centre of Gravity and Base of support:
The centre of gravity is
where the total weight of the body is thought to be concentrated (Encyclopaedia
Britannica, 2014). This is more known as the belly button for most humans as it
is the middle point of our body thus our mass. When setting up for the dig,
Natalie from video 1 gets her body low before the ball has come into view. This
helps her balance and gives her the spring from her legs which produce the
power of the shot. Not only does Natalie get her centre of gravity low to help
balance but as can be seen her feet are at a wide distance apart. This is her
base of support and when this is lower it makes it harder for her to fall over
when performing the shot.
Newton's Laws:
Newton’s first law: This is the law that all things will stay in
motion unless acted upon by an external force. This is also inertia, where the ball
in volleyball will continue to head towards the ground unless it is stopped by
the arms. If this didn’t happen the ball would hit the ground thus scoring a
point for the opposition.
Newton’s second law: Acceleration is dependent on the force and
mass of the ball (The Physics Classroom, n.d.). This acceleration from when the
ball comes off of the forearms is important as it needs to be fast enough that
it goes high enough in the air for the next person to get ready and perform the
set shot.
Newton’s third law: For every action, there is an equal and
opposite reaction (Blazevich, 2010). This law applies to that of the ground
rather than the ball in this instance. When a force is applied to something
which does not move (the ground) an equal and opposite reaction comes off the
ground. In the push-like motion which is used, the ground enables the force to
be equal which is applied to it.
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