TENNIS STRING TENSION
Landon ChinPhysicsForm A
OBJECTIVE The goal of this project is to determine how variations in
string tension of a tennis racquet will affect playability A playability score was generated for three different string
tensions on the same racquet High 65 lbs Med 60 lbs Low 55 lbs
Each string tension was scored by the following: Power Comfort Control Spin Accuracy
PROCEDURE1. String tennis racquet (Babolat AeroPro Drive) at high tension –
65 lbs2. Use a tennis ball machine to project balls to the deuce court
baseline (forehand side)3. Stroke the ball cross-court into the opposing singles deuce court.4. Record the placement of ball landing5. Repeat for 70 forehand strokes6. Record score (out of 10) for
1. Power 2. Comfort3. Control4. Spin5. Accuracy
7. Calculate overall performance score 8. Repeat steps 1-7 with
1. Medium tension – 60 lbs2. Low tension – 55 lbs
VARIABLES Forehand stroke repeatability Bounce of tennis balls projected from machine
Dead balls were ignored Height of ball bounce on racquet impact
Effort to keep stroke consistent for each ball String tension loss after stringing
Racquet was tested the same day as strung to minimize tension loss.
Contact location and on stringbed Effort to stroke ball in sweetspot of stringbed
Racquet head angle on contact Consistent natural topspin stroke (Western Grip)
HYPOTHESIS 55 will have the most power and topspin 55 will have most comfort 65 will have the best ball placement and
accuracy 55 will have the highest score, then 60 and
65 60 will highest score combination of power
and control Comfort will have the least change between
string tensions Power and Accuracy will have the most
change
WHAT IS TENNIS STRING TENSION? Tightness at which the strings are set in the
frame of the tennis racquet Affects the power the racquet will generate
and transfer to the ball Tension affects power, control, and comfort Most racquets have a recommended tension
range Typically 50 – 60 lbs or 55 – 65 lbs
Higher tension: more control, less comfort Lower tension: more power, more comfort Racket strings return 90% of force Tennis balls return 55% of force
TENSION: SHOT POWER & BALL CONTROL In general, lower tension produces more power Lower tension allows the strings to bend more when
striking a ball Stores more energy before it whips back transferring it
into the ball Control is defined as the ability to place the ball with the
desired speed and spin to a particular area of the opponent’s court
Affects the ball opposite of power More tension – More control
A tighter strung racquet will cause the ball to deform more when it contacts (since it is more like striking a solid wall) which allows the angle at which it bounces to be more exact than the trampolining caused by looser strings
OBSERVATIONS65 60 55Below average power;ball lands short of service line; stiff on contact; average topspin; good accuracy and ball placement; good control; lacks power
Above average amount of power; ball lands around the service line; nearly no stiffness; average topspin; decent accuracy and ball placement; good combination of power and control
Lots of power; Ball lands around baseline; No stiffness; good to topspin; Low accuracy and ball placement; great power, control liability
OBSERVATIONSTension Power Comfort Control Spin Accurac
yOverall
65 5 6 9 7 9 36
60 8 8 8 7 8 39
55 9 9 5 8 5 36
VELOCITY AND FORCE COMPONENTSa) Velocity components on impactb) Force components of ball on
racquetc) Reaction force components of
racquet on ball FN – normal (perpendicuar)
forces pushes the ball off the strings and responsible for the racquets power
Fr – friction (parallel) forces influences the rebound angle by slowing the ball's tangential speed as it slides across the stringbed (vx), and it changes the speed and direction of the spin (ω)
Reaction force increases with decreasing string tension
BOUNCE MODEL FOR BALL INCIDENT ON STRINGS
The symbols represent the following parameters: ω1 — The angular velocity (spin) of the incident ball
(radians/sec). ω2 — The angular velocity of the rebounding ball
(radians/sec). v1 — Incident velocity of ball (m/s). v2 — Rebound velocity of ball (m/s). vy1 — Component of incident velocity perpendicular to
stringbed (m/s). vy2 — Component of rebound velocity perpendicular to
stringbed (m/s). vx1 — Component of incident velocity parallel to stringbed
(m/s). vx2 — Component of rebound velocity parallel to stringbed
(m/s). θ1 — Incident angle measured from perpendicular to
stringbed (degrees). θ2 — Rebound angle measured from perpendicular to
stringbed (degrees). F — Friction force acting opposite to the direction of the
bottom of the incident ball (Newtons). N — Normal reaction force of strings on ball (equal and
opposite of force of ball on strings) (Newtons). R — Radius of ball = 0.033 m. D — The offset distance between a radius to the center of
mass and the net action of the normal force (mm) Vx — Component of racquet impact point rebound velocity
parallel to stringbed (m/s). Vy — Component of racquet impact point rebound velocity
perpendicular to stringbed (m/s).
STRING DEFLECTION &BALL DEFORMATION
BALL DEPTH VS. STRING TENSION
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HIGHLOW
MED
HIGH TENSION BALL PLACEMENT
HIGH TENSION BALL PLACEMENT
LOW TENSION BALL PLACEMENT
MED TENSION BALL PLACEMENT
TENSION VS FLIGHT PATH Ball clearance over the net increased with
decreasing tension which indicates that lower tensions produce greater rebound angles off the racquet stringbed
LOW
HIGHMED
CONCLUSION 60 had the highest score 55 had most topspin and power 65 had highest control Spin changed the least Control, Accuracy, and Power changed the most Recommended tension for power: 56-58 Recommended tension for control: 62-64 Recommended tension for consistency: 59-61 Extreme power: 55 and lower More control: 65 and higher I would use a tension slightly lower the 60 to I can
keep the ball deep without overhitting
SOURCES Global Tennis Network Livestrong Tennis Warehouse University Tennis Warehouse About.com Ezine Articles Journal of Sports Sciences