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The correct answers for the Quiz are in green text.
Question 1

What factors control the rate of a jumpers spin about the bar?

  1. How much you throw your arms toward the bar on takeoff.
  2. Your curve radius and running speed.
  3. Your lean angle at plant, your lean angle at takeoff, and how long you are on your takeoff foot during the takeoff drive.
  4. How much you arch toward the bar during your takeoff.
Explanation:

If you chose answer 3, congratulations! If you subtract your bank angle at takeoff from your bank angle at plant, you get the angle through which you rotated during your takeoff drive. Divide that by the time your takeoff foot was on the ground and you get the average rotation rate during the takeoff drive. This is approximately the rotation rate at takeoff.

If you chose answer 2, You had it partly correct. Your curve radius and running speed combine to give you your bank angle.

Question 2

How many strides should you take in your curve?
  1. 2 or 3 strides.
  2. 3 or 4 strides.
  3. The number of strides in your curve depends on your curve radius and may be a fractional number like 3 1/4.
  4. Half of your total number of strides.
Explanation:

If you chose answer 3, congratulations! Your curve radius controls your angle of bank at plant, which is one of the things that controls your rate of spin about the bar. Since you must carefully control this rate of spin, you must also carefully control your curve radius.

If you chose 1,2, or 4, you would be starting your curve "on" a specific stride. Starting your curve on a specific stride limits your choices of curve radius, or forces you to run a complex curve.

Question 3

What causes the jumper to cross the bar
and land in the pit?
  1. The jumper must developed enough centrifugal force during the takeoff to throw himself/herself over the bar.
  2. The jumper's horizontal velocity that is left over after takeoff.
  3. The jumper has to leave the ground with his/her body angled toward the bar.
  4. The jumper must drive the arm closest to the bar over the bar.
Explanation:

If you chose answer 2, congratulations! The jumper's residual horizontal velocity should be used to carry him/her across the bar and into the pit horizontally.

If you chose answer 1, you have a basic misunderstanding about the physics of a body moving along a curved path. When you are moving along a curved path, as you would riding in a car that is turning, you feel as if there is a force pushing you toward the outside of the curve. What is really happening is that, in order to stay in your seat, you are exerting a force on the car in the direction of the center of the curve it is traveling. If the car door is open, and you let go of your seat, you will continue traveling in whatever direction you were going when you let go. At first it will appear to you that you have been thrown out of the car in a direction that is 90 degrees to the direction the car is traveling. However when viewed from the top the truth is revealed. Click FIGURE 1 in the right sidebar of this page to see a demonstration of what really happens. And don't feel bad that you didn't understand what is really happening. The idea for this answer came from a paper on high jumping written by one of the "top dogs" in US high jump coaching.

Answer 3 is wrong  because taking off angled toward the bar wastes energy and makes it difficult to develop the rotation about the bar that is needed to keep your feet from knocking the bar off on the way down to the pit.

Answer 4 is also wrong because having your arm out over the bar during the takeoff absorbs some of the energy from the jump.

FIGURE 1
Click on the image to see the animation.

Imagine that you are in a car that is driving in a circle. The string represents how you are hanging on to your seat. When the string breaks, watch which direction the ball goes. It continues in the same direction it was going (arrow A). It is not "thrown out" by centrifugal force. If it were, it would have gone in the direction of arrow B.

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