Jumping and Hang Time by Mel Siff
Since we have recently been discussing great vertical jumps, the following
Q&As should be of interest to list members:
<http://netra.exploratorium.edu/sport/faq11.html#anchor445332>
Q: How does Michael Jordan manage to hang in the air for so long when he goes
up for a slam dunk?
A: Actually, he doesn’t hang in the air any longer than any other basketball
player. It just looks that way. Once he leaves the ground, Jordan is governed
by the same laws of physics as the rest of us. How high he jumps depends
entirely on how much force he generates with his legs as he leaves the
ground. And how long he stays aloft is directly related to the height of the
jump: the higher the jump, the longer he stays in the air.
A vertical jump of four feet leads to a hang time of one second. That’s an
unusually high jump and, it turns out, most basketball players, including
Michael Jordan, don’t jump that high. A three-foot-high jump has a hang time
of 0.87 seconds. All the artistry of a slam dunk takes place in just eight-
or nine-tenths of a second!
Jordan makes it seem longer because he holds onto the ball longer than other
players before shooting or dunking, waiting until he’s on the way down to let
go of the ball. His tendency to pull his legs up as the jump progresses also
makes it seem like he’s staying higher than he really is.
Next time you watch the Bulls play, try to time how long Jordan stays aloft
and compare it to other players’ hang times. You’ll see there’s not much
difference.
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Q: Why do long jumpers “run” several steps in the air after they take off?
<http://netra.exploratorium.edu/sport/faq7.html#anchor452653>
A: The hitch-kick, as the running motion is called, stops the forward
rotation of the jumper’s body that he gets when he springs into the air. As
the jumper plants his foot for takeoff, the motion of his lower body stops
for the fraction of a second his foot is in contact with the board. But his
upper body continues to move forward, which makes him start to rotate forward
around his center of gravity. If unchecked, this rotation would send him
face-down into the sand.
Long jumpers have learned to counteract this rotation by moving their hands
and arms in the hitch-kick. During the hitch-kick, jumpers hold each leg
straight as it moves backward and bent at the knees as it comes forward. This
difference in leg position causes the jumper’s lower body to move forward.
Similarly, the jumper’s arm movements during the hitch-kick pushes the
jumper’s upper body backward. These body motions neutralize the takeoff
rotation and allow the jumper to get into a better position for landing
When the jumper stops hitch-kicking, the take-off rotation continues
unchecked. The jumper rotates forward around a line that goes from side to
side through his center of gravity. This rotation forces his legs (now
stretched out in front of him) downward.
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Mel Siff
Denver, USA
Mel Siff Dot Com
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