The Forehand: Slice vs. Topspin
Pranav Reddy
Background
The 3 basic strokes:
-topspin- offense or defense
-slice: defensive
-flat- offensive
I will concentrate on the first two
Grips
Professional Topspin shot
• http://www.youtube.com/watch?v=pM0jYWf
VFMw&feature=related
Professional Slice
• http://www.youtube.com/watch?v=wFcamvU
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Kinetic Chain
-Power in tennis is generated via muscles
working together as a chain
-transfer of energy from one part of body to
another
-the arm alone won’t generate enough power
Kinetic Chain: Transfer of energy
• Kinetic chain starts in lower body
• Begins in feet: power is created as feet push
off ground
• Lower legs (calves)
• Upper legs (quadriceps and hamstrings)
• Gluteus maximus
Kinetic Chain: Transfer of Energy
- Energy then transferred to hips( abductors
and adductors) and core; used for rotation
- Pectorals
- Shoulder(deltoids)
- Upper arm (biceps)
- Forearm (brachialis)
- hand
Tennis Injuries
But I will focus on more common
injuries…
Overuse Injuries
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Tennis elbow
Bursitis of elbow
Rotator cuff tendonitis
Shoulder tendinitis
Frozen shoulder
Wrist tendonitis
Acute Injuries
• Wrist sprain
• Shoulder separation
• Torn rotator cuff
• Therefore proper form and training needed
Experiment
• Compare the topspin and the slice shots
• Differences in racquet contact
• Differences in spin
• Differences in translational kinetic energy
• Differences in rotational KE
Contact and spin
• slice stroke: racquet head cuts under the ball
• topspin: racquet face comes over the ball
• This difference in contact leads to differences
in KE
• See my videos
Differences in KE
• KE=1/2(mv^2)
• KE is transferred from racquet to ball
• Rotational KE(1/2 Iw^2)
• See results next slide
Topspin: Translational KE
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Mass of tennis ball: 0.58 kg
Initial X- velocity of ball: 1.81 m/s
Initial Y- velocity of ball: 1.32 m/s
total initial velocity: 2.24 m/s
Initial KE= 0.5(0.058)(2.24^2)=0.1455 Joules
X-velocity after: 20.2 m/s
Y-velocity after: 10.4 m/s
Total velocity after : 22.72m/s
KE after: 0.5(0.058)(22.72^2)=14.97 Joules
Topspin: KE Rotational
• assume ball is coming at racquet with no spin; rotational KE is not a
factor before impact
Rotational KE after
• 1 revolution of ball took 4 frames
• Camera shot in 240 frames per sec
• Time for one full rev (T)= 4/240= 0.0167 sec
• Angular velocity(w)= 2pi/T= 376.3 rad/sec
• KE=0.5(I)(w^2)=0.5(3.96e-5)(376.3)=0.0074 J
• Note: the moment of inertia of tennis ball(hollow sphere) is equal
to 2/3(m)(r^2)
• Now lets compare with slice….
Slice: Translational KE
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Initial X- velocity of ball: 1.85 m/s
Initial Y- velocity of ball: 1.37 m/s
total initial velocity: 2.30 m/s
Initial KE= 0.5(0.058)(2.30^2)=0.1534 Joules
X-velocity after: 14.7 m/s
Y-velocity after: 5.1 m/s
Total velocity after : 15.56m/s
KE after: 0.5(0.058)(15.56^2)=7.02 Joules
Slice: KE rotational
• Again, assume ball is coming at racquet with no spin;
rotational KE is not a factor before impact
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Rotational KE after
1 revolution of ball took 7 frames
Camera shot in 240 frames per sec
Time for one full rev (T)= 7/240= 0.029sec
Angular velocity(w)= 2pi/T= 216.7 rad/sec
KE=0.5(I)(w^2)=0.5(3.96e-5)(216.7)=0.0043 J
Note: the moment of inertia of tennis ball(hollow
sphere) is equal to 2/3(m)(r^2)
KE transfer
• A total of 14.83 Joules were transferred from
racquet to ball in the topspin shot
• Whereas only 6.87 Joules were transferred in the
slice shot
Topspin case: 99.95% of ball’s KE after impact was
translational
Slice case: 99.94% of the ball’s KE after impact was
translational
Conclusions
• Regardless of the type of shot, the rotational KE of ball after impact is very
little compared to the translational KE of the ball after impact. The ratios
of rotational KE to translational KE after impact were essentially the same
for both shots.
• The type of shot certainly affects the amount of energy transferred from
the racquet to the tennis ball.
• The topspin shot had a greater rotational KE transfer compared to the
slice. This is expected: the racquet comes over the ball faster in a topspin
shot than it does in cutting underneath the ball in a slice shot. If the
racquet cuts too fast under the ball in a slice, this will result in a drop shot
rather than a normal slice.
• The topspin shot also had a greater transfer of translational KE. This is
expected since the topspin is more of an offensive shot therefore it is hit
with a greater velocity, while the slice is more of a defensive shot and
therefore is expected to involve a smaller transfer of translational kinetic
energy.
Further Investigation
-Many possibilities for future experiments
• Elasticity of strings: certain types and tensions
• The flat shot: quite powerful
• two handed vs. one handed: different players
have different styles
Further Investigation
Why does forehand tend to be more powerful
compared to backhand?
-uses deltoids and biceps rather than weaker
muscles(triceps and anterior shoulder muscles)
-uses more hip due to open stance, therefore
more rotation
References
http://sportsmedicine.about.com/od/tennisinju
ries/a/tennisinjuries.htm
http://www.livestrong.com/article/105577muscles-body-used-tennis/
https://www.msu.edu/~jochmans/physicsoften
nis.html
Thank You