# Mechanical Principles

## The Rules of Sport Skill Technique

Mechanical principles applied to sports are rules that govern the efficient execution of skills. Using these rules as guides, athletes can build excellent technique and gain the greatest mechanical advantage. Newton's Laws of Motion are the foundation for these mechanical principles, which must be applied in concert with other sports training principles to achieve higher levels of sport performance.

## Principles from the Law of Inertia

1. To achieve skilled movements, athletes must effectively combine linear and angular motion. For example, a discus thrower's body must move in a straight path from the back to the front of the ring while rotating with increasing velocity.

2. When two or more motions are required, athletes must execute movements continuously in sequence. For example, if a javelin thrower hesitates or stops at the end of the approach just prior to the throw, the advantage of the the approach is lost.

3. Athletes can increase mass and/or velocity to realize proportional gains in momentum. For example, if a football player gains both weight and speed, it is more difficult for an opposing player to alter his path.

4. Transfer momentum efficiently from each segment to the whole body. For example, a sprinter coming out of the starting blocks uses the driving action of his or her arms to contribute to the total momentum and direction of the body.

## Principles from the Law of Acceleration

5. Acceleration is proportional to force. For example, a sprinter increases acceleration by increasing the force that he applies against the track. Increasing force by 10% causes a 10% increase in acceleration. If he could lose fat weight but maintain the same level of force (power), acceleration would also increase. See Power Fitness

6. Maximum acceleration is achieved when all body forces are coordinated in the intended direction. Body actions that do not contribute to a skill should be minimized to prevent wasted energy or detract from productive movements. For example, a swimmer coordinates the body actions to generate maximum force while minimizing unnecessary movements that cause excessive bobbing or lateral deviations.

7. When rotating, lengthening the radius slows the rotation and shortening the radius increases rotation. For example, a diver rotates faster when the tuck is tightened, creating a shorter body radius. A pike produces slower rotation because the radius is longer.

8. When jumping, the path in the air is set upon take off. Once a long jumper is in the air, his or her arms or legs may cause body rotation, but the flight path is not affected.

## Principles from the Law of Counterforce

9. Maximize counterforce with stable surfaces. If a surface is stable, it offers the same amount of force back as is generated against it. The less stable the surface, the less counterforce is returned. For example, sand does not offer a stable surface for running as compared to a concrete surface.

10. To achieve maximum jumping height, push directly downward upon take off. The direction of counterforce is directly opposite that of the applied force, and the applied force is most effective when it is perpendicular to the supporting surface because "give" is minimized.

11. Maximize total force. When batting (or for other striking skills), the total force at impact depends upon the both the momentum of the bat and the momentum of the ball.

12. Stay in contact with the ground. In activities involving throwing, pushing, pulling, or striking, one or both feet should be kept in firm contact with the ground until the force application is complete.

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