“What are the
biomechanics behind an accurate jump-shot?”
Introduction
The common basketball shot has developed over the decades.
Over the years biomechanics have become a large part of basketball and the way
a basketball player shoots the ball. The jump shot has become one of the most
common shots used in basketball. The jump shot helps a player elevate their
body above their opponent, this makes it harder to defend and helps to give
power to the shot while giving the player great height when shooting. Perfecting the jump shot also depends on
producing spin on the ball while shooting. The second part of the essay deals
with the question of what effect back spin has on the basketball when shooting.
It is a common practice to shoot a basketball with back spin; my blog/research
will answer what effect back spin has on the ball and in what ways and how back
spin is produced on the ball. Within my question I’ll be asking how spin is
produce in a shot, why back spin should be produced and how this helps when
shooting.
To answer my question I will be using Biomechanics
principles such as describing how Newton’s
law works when performing a jump shot along with Magnus Effect and Projectile
Velocity. These principles along with the skill fundamentals will assist
help to explain how to perform the shot.
The following sub headings will help break down and explain
how to perform an accurate jump shot:
Sub Headings:
What effect does back
spin have on the basketball while shooting?
What effect does the
height release point have on the accuracy of the shot?
How does projectile
velocity affect the accuracy of the shot?
The elements and
fundamentals of the jump shot
When shooting the ball an athlete will release the ball with
a velocity appropriate to move the ball horizontally and vertically to the
goal. Coaching manuals are fairly consistent in advising athletes to
"square up" the body to the basket and jump vertically. A stable base
of support would minimize horizontal motion of the body and create an accurate
shot. The research suggests that coaches focus on a staggered stance and a
vertical jump in teaching the jump shot.
When preparing for a jump shot, facing the basket ready to
shoot, a player should ‘face up’. The feet do not need to be squared up in a
parallel position. While this is not critical, it will help a player to take a
balanced shot. Some players change their stance once they have mastered the
shot, but beginning players need to align their trunk so that their shooting
shoulder is forward and feet are evenly apart facing the basket. The stance can
be evenly spread or slightly staggered and narrow. Slightly staggering the stance allows the
shooter a forward or backward motion while jumping and keeps the body upright
for the shot. This also helps to keep the body aligned with the basket. With
either stance it is recommended to jump from a moderate countermovement. When
jumping there should be a knee flexion of 115-120 degrees. Before jumping the
shooting side foot should be slightly forward and having feet slightly pointed
outwards will provide a stable balanced base for the jump shot.
More advanced players have slight changes in techniques to
produce longer shots; this may include a slight change in forward movement or
less horizontal shift in the shooter’s centre of gravity. It is better to jump
as vertical as possible with a stable base. It is suggested that to achieve
best results the shooter should keep the ball, wrist, elbow and shoulder
aligned with the target basket. It is believed that the traditional jump shot
stance of squaring up to the basket can make it difficult to achieve a
consistent shooting form. It is recommended to developed players to have
staggered stance so that they can align the shooting hand and arm with the
target basket.
Some players have a high release point when shooting the ball;
this can increase the chance of accuracy due to the height of release. When a
player releases the ball from a higher point it decreases the distance the ball
must travel to the target. It also decreases the ball velocity and increase the
angle of the basket making the chances of the ball going higher.
The progression of the jump-shot
Pull up position, knee bend, extend arms, backspin-release ball
To achieve this outcome there are also biomechanical
principles that help execute the shot. They are the following:
Why use back spin
on the ball when shooting?
Magnus Effect
The Magnus effect places spin on the ball. It does this
because the top of the basketball spins over the bottom of the ball which
produces topspin. The air on top of the
ball slows down while underneath the air moves quicker. This causes pressure on
top to be higher. This causes the Magnus force to help the ball dip towards the
basket. In biomechanics terms “The boundary layer would separate
earlier on the top of the ball, because of the collision of the air travelling
around the ball with the oncoming air, whereas on the bottom it would separate
later, so some of the air from the underside of the ball would be dragged
upwards behind the ball”. This causes the air above the ball to push the ball
down along with conservation of momentum (Newton’s third law).
Placing back spin on
the ball increases the chances of making the basket. The ball is designed to
spin back off the ring or back board if the ball is slightly off target. The
basketball is designed to spin due the texture and design of the ball. When
spin is placed on the ball it cause the ball to fall away or ‘break’; this is
due to the Magnus force causing the change of direction. “The downward
reflection of the ball accelerates because the lift forces not only act
downward with gravity, but backward.”(Knudson 2007). This slows the ball down
which allows the ball to have more downward fall or break.
Figure 2
To produce back spin on a basketball there are some easy
steps to follow. Back spin can become second nature to an athlete but they must
learn how to do it properly so that they utilise skill in order to benefit
their shot.
Equations
Bernoulli’s equation,
p + 1⁄2 ρv2 + ρgh = constant
conservation of
momentum, m1v1 = m2v2
Description – Backspin
1. Have your shooting hand underneath the ball with the ball
sitting on the palm of your hand. Have the fingers spread evenly pointing
upwards, the position of your dominant hand will have the biggest effect on the
amount of spin that is produced. Place the non-dominant hand to the side of the
ball so that it is supported - this acts as a guide. Some shooters will place the tip of their
middle finger on one of the horizontal seams to help ensure they get backspin
on a shot. Some shooters can position their hands in this way while the game
and clock is running. Many players will position the tip of their middle finger
on the horizontal seam while shooting a free throw. This is because they have
more time to position the hands in the right spot.
2. The shooter should form a 90-degree angle at the elbow
(dominant hand) as they get ready to shoot the ball. There should be a 90
degree angle at the elbow and a 90 degree angle at the armpit. Making the 90 degree angle allows the shooter
to fully extend the arm as they make the shot.
3. The shooter needs to extend their arm and snap their
wrist in a downward motion in order to produce backspin on the ball. As the
shooter brings their fingers down, the fingertips should push the ball out of
their hands, while doing this the shooter should pull the seams of the
basketball downward. This creates the backspin on the ball. The middle finger
(of the dominant shooting hand) should be the last one (finger) to come off of
the ball while the shot is being made. This middle finger has the most impact
on the direction and backspin of the ball.
How does
projectile velocity affect the accuracy of the shot?
When taking a basketball shot you are trying to achieve a
high release point so that you can project the shot at the highest point so as
the ball falls away it goes through the hoop. When describing the projection of
the basketball you need to work out the relative height of the projection. This
is the projection point of the ball and where you want the ball to land. If the
projection release point of the ball is lower than the target of the hoop, the
relative height is negative. Due to the
relative height being negative the shooter must give the basketball ball extra
flight time. This is done by increasing vertical velocity of the ball and the
angle of projection (Blazevich 2007).
Projectile velocity of a shot
Figure 3
What effect does
the height release point have on the accuracy of the shot?
When producing the jump for the jump shot, the player is
applying Newton’s first, second and third laws and the Law of Gravitation. The
first law is applied when the player overcomes inertia by having a force
applied against him, which is Newton’s second law, F=ma. To achieve the jump
the player needs to “apply a large and well-directed force against the Earth” (Blazevich,
2007). This action applies Newton’s third law of an equal and opposite reaction
force against the player. Since the force of gravity is acting downwards the
player must produce a large vertical to jump high to increase his point of
release while maintaining a vertical trunk position.
Equations (example) Newton’s Laws
speed = Δd/Δt
velocity (v) = Δs/Δt (rω for a spinning object)
acceleration (a) = Δv/Δt
inertia = m
m·s-1 to km·h-1: x m·s-1 /1000×3600
km·h-1 to m·s-1: x km·h-1 ×1000/3600
The effect of Centre
of Gravity
The centre of gravity can affect the height of release. When
the body stretches out for the jump shot there is less gravitational pull
because of the extension of arms. When the body is fully extended with arms
above the head there is more time in the air. This helps to give the player
more time to make the shot. “By bringing
our legs up under our body after we leave the ground during a jump we would
normally be about to fall back down towards the ground under the influence of
gravity, we rapidly extend our legs downwards, and so, to conserve momentum,
our upper body moves upwards (Blazevich 2007).” This means that while the player’s body’s
centre of mass is moving downwards, their upper body is moving upwards,
relative to their lower body. Therefore their upper body briefly remains
stationary or ‘hangs’.
Answer/Conclusion
To answer my question “What are the biomechanics behind an
accurate jump-shot?” it is a combination of skill technique and biomechanical
principles that makes an accurate shot. If you analyse a basketball player from
the NBA for example Ray Allen, you will see that form of Ray Allen is similar
to the description throughout this Blog. The extension that he reaches to shoot
the ball and the angular range of his elbow to when he snaps the wrist while
shooting is the reason why he is one of the best jump shooters in the NBA. Biomechanics
of this skill is a combination of Newton’s 1st, 2nd, 3rd
law along with achieving the correct the projectile velocity and producing back
spin and understanding the Magnus effect and how much spin should be placed on
the ball. When all these principles are combined, an effective and accurate
jump shot can be achieved.
How are these
elements of basketball used in other sports?
The different elements of the jump shot can be used in a
range of actions in a variety of sports. The Magnus force which produces back
spin on the ball can also be used in other sports. In cricket a fast bowler
uses the Magnus force when he rolls his finger down the seam of the cricket
ball. By doing this his middle finger is the last contact point of the ball,
similar to producing a basketball shot. This back spin is also produced by
snapping the wrist as the ball leaves the hand. These elements are two major
factors that help produce the back spin motion in ten pin bowling, cricket
(bowling), baseball (pitching) and tennis for example. Different biomechanical
actions that are used in basketball are used in sports such as volleyball or
netball. The vertical leap that is produced is a more compact version to a
volleyball spike or block due to the athlete producing a large well directed
force against the surface and then extending their vertical leap. There are
many elements of the jump shot that can be used in other sports, once you break
down the shot; you see the similarities due to the action and the principles.
The principles are used in many sports but in different ways.
References:
Blazevich, A. (2007) Biomechanics the Basics: Optimising
human performance. (1st ed) Chapters 3, 6, 13,. London, UK.
Callaway, C. (2012) LiveStrong. How to get backspin on a
Basketball. Viewed 18 April 2013 <
www.livestrong.com/article>
Fontanella, J. (2007) International Journal of Sports
Science & Coaching, Volume 2, Number 2. The Physics of Basketball.
Baltimore, USA. pp. 197-200.
Knudson, D. (1993) The Journal of Physical Education,
Recreation & Dance, Biomechanics of the Basketball Jump Shot - Six Key
Teaching Points. pp 67 -72, Vol. 64, No. 2.
McGinnis, P. (2005) Biomechanics Of Sport And Exercise. (2nd
ed.) Torques and Moments of Force Maintaining Equilibrium of Changing Angular
Motion. USA. pp. 134-136
It was really insightful.
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