Basketball Resilience Tests

The 1937-38 basketball rules will provide that the
legality of a basketball will be determined by its
bouncing reaction. A simple way to determine this
reaction is to drop the ball from about head height
and observe the percentage of rebound. This method
has been in common use in connection with handball
and tennis. It is a common practice for a handball
player to test balls in this fashion before each con-
test. If the ball appears to have low rebounding
qualities, it is thrown out.

In the case of a basketball, most of this testing
must be done at the factory. Each ball manufacturer
will test the ball to determine the air pressure at
which the required reaction will be secured. The ball
will then be stamped with the air pressure which will
make the ball legal. As far as the school is concerned
it will only be necessary for them to inflate the ball
at-the stamped pressure. However, if rough tests
should be desired by any coach, he may make these
tests by dropping a ball from a height of six feet
and observing the height of the rebound.

In order to determine the optimum bouncing re-
action extensive tests have recently been made. In
these tests, balls made by various manufacturers
were used. The general method was to arrange a

platform six feet above a solid wood floor. Each ball
was then dropped a great number of times and the
height of the rebound was measured. It is obvious
that some spots on a ball have greater resilience
than others. This is especially true of balls whose
panels are sewed together. At the poles of such a
ball there are five heavy seams which come together
in a small circle. In addition there are four thick-
nesses of lining at such a circle. The mechanics of
making the sewed ball are such that it is impossible
to eliminate this deadening factor. Hence when a
ball strikes on a pole, its bouncing reaction is con-
siderably less than when it strikes on some other
part of the surface. Likewise the ball is slightly
deadened if it strikes on a seam. The spot of great-
est resilience is the middle of a panel, Because of
these facts it has been found that a considerable
tolerance must be allowed between minimum and
maximum resilience if balls of the sewed type are to
remain legal. It will be noted that this tolerance
is considerably less for the molded basketballs which
have no heavy seams and which have no particular
dead spot.

Data secured. from one of these series of tests are
shown in the following table:

TESTS TO DETERMINE RESILIENCE OF BASKETBALLS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

G1 $1 S2 Wi W2 G.W. D Wi Ss R W2
Laced Laced Laceless Laced Laceless Laced Laced Molded | Molded Molded | Molded
Comp. Leather
(Resilience Percentage at 13 POUNDS PRESSURE)
Minimum
Rebound 60.5% 54.3% 52.9% 54.2% 54.2% 56.0% 61.5% 65.4% 71.0% 69.6% 63.9%
Maximum
Rebound 64.7% 63.8% | 59.8% 65.4% 58.2% 65.2% 65.5% 69.6% 72.1% 72.3% 64.2%
(Resilience Percentage at 10 POUNDS PRESSURE)
®
Minimum
Rebound 64.0% 71.0% 66.1% 59.4%
Maximum
Rebound 66.1% 72.3% 68.1% 59.6%
(Resilience Percentage at 8 POUNDS PRESSURE)
"Rano 57.0% 65.3% 64.0%
Maximum
Rebound 60.4% 68.1% 65.4%

 

 

 

 

 

 

The above table should be interpreted as follows:
When the Gi laced ball, listed in the first column.
was inflated to 13 pounds pressure and dropped from
a height of six feet it rebounded 60.5% of this height
when it struck on its least resilient spot (probably
a pole) and it rebounded 64.7% of this height when
it struck on its most resilient spot. Another illustra-
tion is: When the W2 molded leather ball was in-
flated to 13 pounds pressure and was dropped from
a height of six feet it rebounded 63.9% of that
height when it struck on its spot of least resilience
and it rebounded 64.2% when it struck on its spot of
greatest resilience. When this same ball was inflated
to a pressure of 10 pounds its bouncing reaction
ranged from 59.4% to 59.6%.

It will be noted that the tolerance for the molded
ball need not be greater than approximately one per-
cent while the tolerance for the sewed ball must be
11 percent if present balls are to remain legal.

If it is assumed that the optimum resilience of a
ball is approximately 60% most of the present sewed
balls should be inflated at a pressure of approximate-
ly 12 pounds (at least less than 13) and the various
types of molded balls should be inflated to a pressure
ranging from approximately 7 pounds to 10 pounds.

Through these and similar tests the National Bas-
ketball Committee hopes to arrive at what is con-
sidered the best reaction of a ball. During the first
year, the tolerance which will be permitted will be
great in order that no present top grade official ball
will be made illegal provided the proper air pressure
is used. It is quite probable that this tolerance will
be gradually reduced so that there will be a narrow
range in the bouncing reaction regardless of the
spot on which it happens to strike the floor or
backboard.

It sheuld be noted that in making a resilience test,
if the ball is dropped from a height such that its
lower surface is six feet above the floor, then the re-
bound should be measured to the lower surface.
Probably the rules will deal in linear measure rather
than percentages and for ease of testing these meas-
urements may be made from the bottom of the ball
when it is dropped and to the top of the ball on the
rebound. This is because the height from which it is
dropped is above the level of the eye and the rebound
is always below the level of the eye. It would be
easy to correlate such figures with the percentages
given in the table above by merely adding 9 inches
(the diameter of the ball) to the linear figures.

(Reprint from May, 1937 Issue of Illinois High School Athlete)