The Hammer Throw is a Track and Field event which involves throwing a 12-16 lb ball secured on the end of a ~ 3.5 ft wire. The other end of the wire is secured to a handle which is used to grip the hammer as it is thrown. The hammer is thrown by gripping the handle and swinging the hammer in a circle, then spinning one’s entire body for 3-4 turns and then the handle is released. A men’s championship collegiate hammer thrower will toss a 16 lb hammer 190 ft or more; the current world record distance (2011) is approximately 285 ft.
A primary concept associated with the hammer (as well as the shot-put) is the ballistic trajectory of the object, used to determine the optimal angle to release the device. The optimal angle is almost independent of the speed of the steel ball when the hammer is released. In a vacuum, the optimal release angle (angle between the velocity at release and the horizontal plane) for maximum distance would be 45°, but the presence of air resistance slows the horizontal velocity of the ball down, making the optimal release angle closer to 42-43°.
Achieving the proper release angle requires some thought and planning. When the hammer thrower begins the first turn, the plane of the hammer swing is considerably lower than 45°, closer to 10°. At the start of the throw, the velocity of the hammer in the ‘orbit’, combined with the radial distance from the thrower to the steel ball, defines the angular momentum of the hammer. As the hammer thrower uses his legs to turn and accelerate the ball, he applies an off-axis torque to the angular momentum, and rapidly turns the orbital plane to steeper and steeper angles, achieving the optimal release angle near 42° in the final turn.
Since most hammer throwers will learn to throw near the optimal release angle fairly easily, the most important factor affecting the final travel distance of the hammer is the speed of the steel ball upon release. Because the hammer thrower uses a circular orbit to throw the hammer, the hammer thrower must exert a centripetal force to keep the steel ball moving on the circular orbit. This force is proportional to the square of the velocity of the hammer divided by the radial distance between the steel ball and the hammer thrower’s body (center of mass), and can easily reach 600lbs or more at release. The ability of the hammer thrower to withstand such huge force is the main limitation in the distance that can be thrown; most hammer thrower perform heavy weight lifting exercises in order to increase their ability to withstand this extraordinary force.
Having developed one’s strength to the maximum feasible, the hammer thrower has additional strategies for increasing the final velocity of the hammer while exerting the same centripetal force. Since the centripetal force depends upon the square of the hammer velocity divided by the radial distance between the steel ball and the hammer thrower’s center of mass, higher velocities can be accommodated (with the same centripetal force ) by increasing that radial distance. Physiologically, this requires allowing one’s arms to extend as far our as possible, so championship class hammer throwers are generally tall, with exceptionally long arms. A particular individual, with a given arm length, can also increase the radial distance by working to keep the steel wire exactly perpendicular to one’s chest throughout the entire throwing motion. In addition, the hammer thrower will substantially increase the orbit radius by completely relaxing the upper body and arms, allowing the arms to dangle completely freely and relaxed as they carry the centripetal force.
At the same time the lower body and legs will drive as explosively as possible in order to accelerate the steel ball as quickly as possible to the final speed. The optimal technique for the maximum hammer throw distance is therefore “schizophrenic”: the upper half of the body is completely relaxed and passive, and the lower half of the body is completely energized with explosive power. This seemingly contradictory combination is what makes the hammer throw one of the most unique and spectacular events in track and field!
By: Dave Kieda, Department of Physics and Astronomy, University of Utah
Articles by Dave Kieda.