Circular Motion in the Discus Throw
By: Catherine Medeiros
In class we have done multiple problems dealing with centripetal acceleration and circular motion. Some of these problems have even included a projectile motion portion of the problem. One sport that deals with circular motion exclusively is the throwing portion of track and field. The events of hammer and discus both deal with starting from rest, building force, and releasing the object to throw it the farthest. When throwing, it is not just about how far you can throw something like a baseball. Behind every state championship disc throw, the thrower is doing physics, specifically circular motion without even thinking about it. I sure wasn't think about it up until this year.
In the discus throw, there is a circle that is 8 feet in diameter. The thrower must remain in the circle for the entirety of the throw, not even stepping on the line. The thrower starts from rest in the back of the circle. They then will swing their dominant leg around 180 degrees. Using their dominant leg, they will power forward across the circle, place their non-dominant leg down quick and turn the remaining 180 degrees. As the thrower turns the remaining 180 degrees, they will open up their arms and release the disc. After the throw, they will continue the motion and follow through.
In the first part of the throw, the initial velocity is zero because the thrower is starting from rest. Once the dominant leg is swung around, the velocity then becomes tangential to the throwing circle as shown below.
As the dominant foot swings around the the thrower has now rotated 180 degrees, the velocity is then changed to be pointing inwards, towards the opposite side of the circle. This is shown below.
Next, as the non-dominant foot is placed quickly down and the thrower again rotates 180 degrees, the velocity is changed to be perpendicular to the velocity shown above.
Finally, as the thrower completes the circle and rotates the last few degrees, the velocity is pointing outwards towards where the throw will land. The ideal position for this is straight down the middle of the sector. During the throw, the throwers legs are used in gaining acceleration and velocity. The velocity is then transferred to the hand so there is plenty of force exerted on the disc to make it go very far. After the thrower releases the throw, the disc turns into a projectile motion. Using the kinematic equations and writing out the data in an XY chart, you can determine the projected distance of the disc, the maximum height, or how long the disc is in the air for.
Many discus throwers have no idea about the physics that is behind every throw they do. If each thrower better understood the physics behind it, they would be able to perfect the angles and ultimately throw farther, overall.
This is a video of what a full disc throw should look like.
In class we have done multiple problems dealing with centripetal acceleration and circular motion. Some of these problems have even included a projectile motion portion of the problem. One sport that deals with circular motion exclusively is the throwing portion of track and field. The events of hammer and discus both deal with starting from rest, building force, and releasing the object to throw it the farthest. When throwing, it is not just about how far you can throw something like a baseball. Behind every state championship disc throw, the thrower is doing physics, specifically circular motion without even thinking about it. I sure wasn't think about it up until this year.
In the discus throw, there is a circle that is 8 feet in diameter. The thrower must remain in the circle for the entirety of the throw, not even stepping on the line. The thrower starts from rest in the back of the circle. They then will swing their dominant leg around 180 degrees. Using their dominant leg, they will power forward across the circle, place their non-dominant leg down quick and turn the remaining 180 degrees. As the thrower turns the remaining 180 degrees, they will open up their arms and release the disc. After the throw, they will continue the motion and follow through.
In the first part of the throw, the initial velocity is zero because the thrower is starting from rest. Once the dominant leg is swung around, the velocity then becomes tangential to the throwing circle as shown below.
As the dominant foot swings around the the thrower has now rotated 180 degrees, the velocity is then changed to be pointing inwards, towards the opposite side of the circle. This is shown below.
Next, as the non-dominant foot is placed quickly down and the thrower again rotates 180 degrees, the velocity is changed to be perpendicular to the velocity shown above.
Finally, as the thrower completes the circle and rotates the last few degrees, the velocity is pointing outwards towards where the throw will land. The ideal position for this is straight down the middle of the sector. During the throw, the throwers legs are used in gaining acceleration and velocity. The velocity is then transferred to the hand so there is plenty of force exerted on the disc to make it go very far. After the thrower releases the throw, the disc turns into a projectile motion. Using the kinematic equations and writing out the data in an XY chart, you can determine the projected distance of the disc, the maximum height, or how long the disc is in the air for.
Many discus throwers have no idea about the physics that is behind every throw they do. If each thrower better understood the physics behind it, they would be able to perfect the angles and ultimately throw farther, overall.
This is a video of what a full disc throw should look like.
Sources:
http://www.topendsports.com/biomechanics/centripetal-force.htm
https://www.iaaf.org/disciplines/throws/discus-throw
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ReplyDeleteDo you use your physics knowledge while practicing your throws? How are throwers precise with their physics measurements and calculcations while practicing?
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