# physics of sports - football and tennis

Post on 18-Jul-2015

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• Flight of a Football

• Round! And remain round! BouncyBut not too much! Water Proof Swift Through the AirAaaand here comes the physics!

• WeightActs downwards alwaysDepends on how heavy the ball is Magnus ForceThe direction depends on the motion of ballDepends on the spin on the ballForce is perpendicularto both spin and velocitySimple application ofBernoullis principleHigher PressureLower Pressure

• Question: Is it always true that the harder you kick the ball, the faster it goes? NO! A new force enters the scene: the Drag Force! Rule of thumb: The greater the turbulence, the greater drag force! Drag Force is proportional to square of velocity. Faster the ball, greater the drag Surprise! Drag suddenly decreases as the separation points coincide!(Image courtesy:Ken Bray article A Fly Walks Around A Football)

• A Rougher Ball is better than a Smooth One Drag Coefficient = Measure of how much drag there is Drag Coefficient falls sooner for a rougher ball than a smooth one Drag Crisis: The fall is rapid!Which is a better football? A Smooth One or a Rough One? The rougher ball movesmore smoothly than a smooth one!!Drag crisis(Graph courtesy:A Fly Walks Around A Football and Journal fo Fluid Mechanics)

• Taking a free-kick = Aiming for a letterbox slit! Weight, spin and drag affect ball trajectory A free kick is not as easy as it seems! Smooth is not always desirable

• All That RacquetTennis

• Rigidity of the stem and flexibility of the head increased Increase in the area of the head Greater adjustability of the tension in the stringsWoodenAluminiumGraphite

• Dead SpotMore bounceSweet SpotCentre of massGrip

• Impact!TranslationRotationFinal movement=+=If the ball is hit just right, there will be no impact on the gripStandard Physics: Every movement can be broken down to a translation and a rotationVcm = VVb = w bSweet spot:Vcm = VbBam!

• The racquet also vibrates!ImpactVibrationThird type of motionGives rise to two sweet spotsCant have both

• Making the case for the central sweet spot even better!Hit the ball right from the middle of the racquet!Hold racquet at the proper grip position

• Sources:http://sport.maths.org/content/Articles on football flight by Ken BrayPhysics of racket-ball interaction by H.Brody, University of PennsylvaniaSweet spots of rackets Hesston College articleBig Thanks to my friends too many to name and they know!Thanks to Arnab Sir and Kulkarni Sir

*N

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