TENNIS STRING TENSION

Landon Chin

Physics

Form 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

PROCEDURE

1. String tennis racquet (Babolat AeroPro Drive) at high tension – 65 lbs

2. 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 55

Below 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 COMPONENTS

a) 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