The Physics Behind The Football Throw

inside science

when you think of football physics is

probably the last subject that comes to

mind but in reality science runs deep

with the pigskin especially when it

comes to throwing the ball

there's the aesthetic excitement of

seeing a beautiful arc and a spinning

ball

tim gay is a physicist and avid football

fan he put together his knowledge of

science and football to help explain it

to fans at university of nebraska

football games the one question that i

got early on which i was unable to

answer is why does a tight

spiral pass turn over

it's thrown with an upward tilt of

perhaps 30 degrees and it descends

hopefully into the hands of the receiver

with a downward tilt of approximately

negative 30 degrees why does that happen

this question puzzled gay for years so

he called in some colleagues as

reinforcements and one although i have

to say that after the team got together

and started worrying about this we still

yelled at each other for about three

years before we finally got it all

figured out

the reason the ball turns over is the

same reason that a gyroscope precesses

what is precession it's the motion of

the axis of a spinning object when there

is an external force acting on the axis

like poking a rapidly spinning top

so gravity is pulling down on the

spinning top and the axis of the top

revolves processes around that vertical

that's what's guiding the ball to turn

over replacing gravity

vertically downward is the on rushing

air which is always pointing in the

opposite direction of the line of

trajectory air is crucially important

our goal was to

solve it in a way we just did more

detailed computer simulations and we

solved it and tried to put it in a form

where the physics took center stage and

was really explaining it in terms of

forces torques and gyroscopic motion he

hopes his findings will give people an

increased appreciation of the game and

maybe give sports fans an interest in

physics it's such a great game because

the ball

isn't some

simple sphere it's a prolate spheroid

which causes all kinds of crazy stuff

just ask you know ask a punting team

what the ball does when it lands it's

unpredictable

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