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TW University -- -- Home Racquets v Strings v Strokes v Customize v Balls v Shoes v Other v Tools Racquet Recommender Racquet Performance Analysis Similar Racquets Compare Racquets Power Sweet Zone Size Plow-through Shot Speed Hittingweight Racquet Contribution Shot Trajectory Vibration Spin Window -- Multi-View Tool -- Experiments Effective Racquet Mass Racquet Control — Part 1 Free-standing vs Hand-held Racquet Testing Spin Demo Racquet Weighting Spin Setups Spin & String Pattern Spin & Impact Location Articles Racquet Power Scoring: Why Count One Point as Fifteen? Why You Sometimes Hit the Ball Out The Total Performance Measurement Does the Racquet Matter? Racquet Specs and Power Power Potential Basics Shot Speed Basics Racquet Power and Shot Speed Maximum Shot Speed — Where To Hit on the Racquet -- Power Imbalance and What It Means -- Racquet Power Terminology Spin & Trajectory Definitions Weight, Balance and Swingweight How To Measure Swingweight Power Potential Test Method -- Tools Find Similar Strings Compare Strings String Performance Database String Stiffness Spin Potential String Friction Ball Friction Performance Database String Friction Tool Impact Photo Gallery -- Experiments Variable Tension Stringing for Spin Temperature and String Tension Spin and String Surface Roughness Single String Impacts Spin and Racquet Setups Spin & Material Spin & Static Friction Spin & Sliding Friction Spin & Ball Friction Spin & String Pattern Spin and String Movement Spin & String Snap-Back Spin & String Stiffness Spin & String Lubrication Spin & Impact Location Strings 'Going Dead' P1 Strings 'Going Dead' P2 Articles Why Is String Stiffness So Important To Power? String Stiffness: The Alpha and Omega of String Performance String Stiffness — How It Works Spin and String Movement -- Tools Compare Strokes Shot Helper Tool Racquet Head Speed -- Experiments Customizing Strokes & Power Kick Serve Physics Strokes & Pendulums Articles Kick Serve Physics Strokes & Pendulums Spin and Trajectory Definitions and Analysis -- Tools Customization Tool Customization Worksheet Swingweight Tool Experiments Customizing Strokes & Power Articles How To Measure Your Racquet's Swingweight Maximum Shot Speed — Where To Hit on the Racquet Weight, Balance and Swingweight Explained Tools Shot Trajectory Experiments Tennis Ball Trajectories: Aerodynamic Drag and Lift in Tennis Shots Tennis Ball Properties Articles Ball Testing: Return Deformation Tools Footwear Cushioning Tool Footwear Traction Tool Experiments Tennis Shoe Cushioning: Impact Testing To Compare Tennis Shoes Tennis Shoe Traction: Developing A Test Rig To Measure Shoe Traction On Tennis Courts Foam Cushioning Properties: Choosing Material for Tennis Shoe Soles Hockey Experiments Hockey Stick Contribution to Puck Speed in Slap Shots Introduction to the Physics of Hockey Sticks Flex of a Hockey Stick Hockey Stick Flex Profiles Hockey Stick Kick Point Swingweight of Hockey Sticks -- NEW! Videos and Podcasts Lacrosse ball impact with wood beam. NEW! Experiment How Does The Ball Know How Fast To Bounce? How does the ball know how fast to bounce from a beam or a racquet? You say that is a silly question — it is determined by the forces of the collision which depend on the properties of the colliding objects. Well, yes, but how do the colliding objects know their own properties? Again, a silly question, you say. They just are. Mass, length, balance, and stiffness of an object just are . . . or so you think. Rubber band stringbed. NEW! Experiment In Search of More Spin — The Edge Effect and Variable Tension Stringing Method The center two mains were tensioned to 60 lb with each adjacent main decreasing in tension by 5 lbs, with the last string at the periphery at 20 lb on each half of the racquet. The cross strings were all tensioned at 50 lb. Did this variable string tension method to produce more spin? Geometry of impact. NEW! Experiment Racquet Control — Part 1 Factors that might affect racquet control were investigated by setting up a simple experiment where a tennis ball was fired from a ball machine to impact a hand-held racquet at rest. Speed, angle and spin were measured for rebounds from the racquet in its natural condition and with mass added. Free-standing impact. NEW! Experiment Racquet Support Method For Testing — Free-standing vs Hand-held Experiments analyzing racquet performance during collisions with tennis balls use several methods to secure the racquet — free-standing, hand-held, head-clamped, and handle-clamped. The concern is that the securing method can alter performance. Each method allows or prevents certain degrees of freedom of movement. All have major drawbacks except free-standing and hand-held. The main concern between these two is that although a hand-held racquet allows all degrees of freedom of motion, it may alter the magnitude of these motions and thus the performance and assessment of the racquet. The theoretical consensus is that the ball leaves the strings before it receives any information from the handle on whether it is hand-held or free. We test that here. Video still of upward moving racquet NEW! Experiment Spin Demo Just because you swing upward does not mean you will get topspin, swinging down does not mean you will get backspin, and swinging flat does not mean no spin. You can get top, back, and no spin from all swing trajectories. Using 18 videos of simple demonstrations and the technique of drawing "relative path" diagrams, this experiment explains the how and why of rebound spin and direction. NEW! Tool Racquet Recommender Tool Racquet Recommender Tool The Racquet Recommender tool helps players find racquets that have more or less of user designated performance properties: Power, comfort, control, maneuverability, and spin. The player's current racquet is represented by the green line on each slider, and as the sliders are moved, racquets (dots on the graph) disappear or appear. The details and comparisons of these recommended racquets are obtained by clicking the green go button. NEW! Tool Racquet Performance Analysis Tool Racquet Performance Analysis Tool The interactive TWU Racquet Performance Analysis Tool compares the shot performance of every racquet to every other in 9 areas —shot ... Speed Distance Spin Launch angle Flight time Swing speed Power Power zone size Plow through Racquets can be filtered and compared All at once, or by brand, or choose any 2 or 3 to compare. By headsize, swingweight, weight, balance, twistweight, or vibration frequency. By swinging with the same effort or the same speed for each racquet. By on-center and off-center hits. OTHER FEATURES Similar racquets: Highlight and compare all similar racquets to each other. Customize racquets: Customize racquets and show the result compared to all other racquets. Help buttons, icons and screens: Multiple information sources for explanations, definitions and terminology. Interactive: Simply click on any of the dots or choose from the dropdown menus in the Control Panel. Tennis ball into head wind Article Why You Sometimes Hit the Ball Out Ever since tennis was first introduced as a serious sport, players have been blaming their racquet or the ball for the mistakes they make. That is why professional players need six identical racquets each match, all freshly strung, and why each ball is closely inspected for fluffiness before it is deemed suitable to be served. Any tiny variation is enough to throw even a professional off balance. How then do players cope with changes in air pressure, temperature, humidity, ball mass and diameter, fuzziness, altitude, wind? All of these factors affect the flight of a ball through the air, so they affect where the ball lands. Impact on layered foams Experiment Foam Cushioning Properties Cushioning is an important performance characteristic of tennis shoes. It is accomplished by altering the geometry, thick...