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Why is it good to throw a spiral?

Why does a football travel farther when it is in a spiral motion? Joe Staley asks Sal Khan about how a spiral is thrown and why the ball travels farther in a spiral. This content is provided by the 49ers Museum Education Program..

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Video transcript

hey Sal why is it good to throw a spiral and why does it go farther and that's a great question Joe and it all boils down to angular momentum and before I even talked about spiraling footballs I'll talk about a little toy that we're all familiar with from our childhood and that's a spinning top when you spin a top it seems to defy gravity a little bit it'sit's able to spin on this little this little pin at the bottom of the top and if you even push it one way or another it seems to stay upright that the spinning motion somehow seems to stabilize the top it does it just doesn't topple over one way or another if you just put a top straight down without spinning it it's sure to just just topple over one side or another and the reason why a top doesn't topple is because of its angular momentum so the way that I've drawn this spinning top right over here if you look at it from above the top this would be going in the counterclockwise direction it's a the convention would be that it's angular momentum vector we're not going to have to go too deep into vectors would would point upwards and the direction doesn't matter so much as the overall dimensionality that it's in this upward downward direction and so as the top spins is going to try to it's going to allow the the entire thing to be stabilized in that direction you push it a little bit to the left it's going to move a little bit to the right you push it a little bit to the right it's going to move a little bit to the left and try to stay in that stable up-down direction now that should give you a pretty good clue of why it's nice to spiral a football if you spiral the football while you throw it so this football is going to have some angular momentum due to the spiral over here I've drawn the arrows to show the direction in which it is spiraling and it's also going to have it's also going to have some linear momentum the linear momentum is going to be the direction the direction of its flight now let's compare that to a football that only has linear momentum that is not that is not spinning around so the foot this football over here the one that you throw a spiral we have to remember we're not throwing these footballs in space we're throwing them on football fields and there's air otherwise we wouldn't be able to breathe and so there's all this air around and footballs as we all know are not are not very normal shaped looking things they're not perfect spheres they have this somewhat strange football shape and so you could imagine on that football shape the wind is doing all sorts of things and if the if the football wasn't if the football wasn't spinning that it's very easily it's very easy to destabilize the orientation of the football the wind if the football going in that direction and the wind is coming the other direction while the football is going to start flipping over so this football right over here if it's not spinning well then it might start to flip like that actually let me just draw the flipping on that football itself it might start to flip around it might start to flip around like that and as it flips around it'll become even less aerodynamic when the football is in an orientation when the football is like in an orientation like this and if it's trying to go against the wind so if it's trying to go in that direction well then it's getting a lot of wind resistance to so this is the we do the wind in a blue color so this is the wind coming in hitting that football and even creating even more destabilizing forces and that's why you see when someone throws either no spiral or an imperfect spiral no matter how carefully they try to orient that football it's going to start fumbling and flipping around on the other hand if you have a nice spiral that spiral that angular momentum is going to keep just like a top is going to keep the football oriented it's going to keep the football oriented in its most aerodynamic position the most aerodynamic position is if the point of the football is going into is going into the air and so this football even if there's a little bit of air that might want to destabilize it that way or might want to destabilize it that way because it's like a spinning top it's going to keep adjusting itself to be to be pointing in that optimally aerodynamic that optimally aerodynamic orientation which will allow it to cut through the air in an optimal way and not start fumbling or bobbling around in the air badly like a badly thrown football or sometimes you might even see it with a punt or a kick that footballs are very unpredictable if they don't have that tomorrow that the air is going to take them in all different ways so not only will this allow the football to travel farther because it's going to cut through the wind better and not be destabilized into a less aerodynamic position but it's also going to be more accurate if the football is flipping around like the scenario on the right it's very hard for the quarterback to get it to the intended receiver and it's very hard for the receiver to predict where the ball is going to be with a nice spiral the foot the quarterback could be more precise and the receiver is going to have a better chance at predicting where the ball is going to be so hopefully that helps