Somersaulting – Angular Kinetics Angular kinetics is concerned with the generation of rotations and the control of these rotations. All objects posses inertia and do not wish to begin rotating. If an external moment of force is applied to the object, it will experience an angular acceleration. Sport Books Publisher

Off-center External Forces Any external force that acts away from the body’s center of mass will create a moment of force acting on the total body Usually, the off-center force is a reaction force from the ground or equipment, resulting from the internal muscle forces generated by the athlete If an athlete has forward momentum and a pivot point is created, then some or all of the linear motion can be transferred into angular motion Sport Books Publisher

Transfer of Momentum Within the Body Sometimes athletes accelerate specific body parts while in contact with the ground. Upon leaving the ground, athletes lock these segments to the rest of their bodies. The joint angles these segments make with the trunk become fixed. The momentum created by these segments becomes part of the momentum of the total body. Sport Books Publisher

Rotations While Airborne Rotations cannot be generated when airborne. Once the body is airborne, only gravity acts on the body. The angular momentum (the amount of angular motion) is conserved. Changes in body shape will decrease/increase the moment of inertia about the somersaulting axis. If the moment of inertia increases, the athlete will have more reluctance to rotating and will have slower angular velocity. Sport Books Publisher

The inverse relationship between moment of inertia (I) and angular velocity (ω) Sport Books Publisher

Qualitative Analysis of Human Motion The study of human motion, in the absence of measuring, by observing a movement and applying biomechanical principles in assessing performance. It is subjective and yet systematic evaluation of a movement or skill. It is based on a direct visual observation of a movement or its video recording. It is dependent on the constraints or limitations of an event or performer. Sport Books Publisher

Integrative model of qualitative analysis Sport Books Publisher

Skill Objectives An objective can be described for all skills Secondary objectives refer to the speed of the movement or the accuracy required Skills with similar overall objectives are governed by similar biomechanical principles Sport Books Publisher

Analyzing a Skill Divide the skill into phases (preparation, execution, follow-through) Determine the biomechanical criteria for each phase (in the execution phase, shot putters must maximize the velocity of the shot prior to the takeoff) Identify the key body movements involved in each phase (in the preparatory phase of the soccer kick, the foot of the stance leg is placed beside the ball) Sport Books Publisher

Observation of Performance Before going to practice, identify the skill you wish to observe and why. Be specific regarding the phase, body movements, and related biomechanical criteria. It is important to keep the surroundings as uncluttered as possible and to minimize distractions. Estimate how many times you have to view the skill. Use all your senses to observe a performance. Ask the athlete questions to confirm your observations. Sport Books Publisher

Good coaching includes asking Athletes if given instructions were understood correctly, particularly Under distracting environmental conditions, i.e., noise, distance, low visibility, etc. Sport Books Publisher

Error detection Visual observation (use direct observation, video, or observe traces left by the athlete) Observe the outcome or follow-through Use a checklist Ask athletes how they felt during the performance Avoid comparison with an ideal form or mental model Sport Books Publisher

Error Correction Usually done verbally, with visual feedback, or using mental imagery Begin with the earliest occurring error Correct only one or two faults before re-observing the skill Accept that error correction is an ongoing, multi-step process Use positive and specific language appropriate to the age, developmental level, and competitive level of the athlete Ask for feedback Sport Books Publisher

In sports where there is a considerable distance between the coach and the athlete, a walkie talkie or other long-range communication device comes in very handy. Sport Books Publisher

In this chapter you have learned: How to generate Free Body Diagrams of the body using the particle and stick figure models Those factors affecting the height and range of a projectile How the forces of air resistance, drag, and lift affect projectile paths The role of impulse and impact on many sporting activities The body actions affecting throw-like and push-like skills How angular motion is generated when somersaulting How angular motion is manipulated while airborne A technique for performing a biomechanical qualitative analysis of a skill Some tips on performing error detection and correction Sport Books Publisher

Discussion Questions: 1. Define Biomechanics. Briefly discuss each of the components in the model of Biomechanics presented. 2. Discuss three ways in which Biomechanics would be helpful to a coach. 3. Apply each of Newton’s three laws of motion to a skill from your sport. Be specific in identifying forces, masses, accelerations, etc. 4. Briefly discuss how you would advise an athlete in maximizing impulse and minimizing the harmful effects of impact. 5. List advantages and disadvantages of the particle and stick figure models. 6. What factors affect the horizontal distance of a projectile? Which factor is most important? 7. Differentiate between throw-like and push-like patterns of motion. Give examples of each. 8. Select a sport skill in which a light object is thrown. Discuss the effects of air resistance on the path of the object. 9. Identify three ways athletes can decrease drag forces acting on their bodies. Sport Books Publisher

Discussion Questions: 10. Identify two sport skills in which lift forces have a large effect on the resulting motion. 11. Differentiate between equilibrium, stability, and balance. 12. For a skill from your sport, identify how one maintains or loses balance. 13. Draw a free body diagram of a diver during the takeoff phase with the board. Identify all possible ways the diver may increase the amount of rotation. 14. Discuss the relationship between moment of inertia and angular velocity. 15. Analyze a skill from your sport biomechanically. 16. Prepare an observation plan to observe the above skill from your sport. 17. Draw a series of free body diagrams to represent the human body during each phase of the above skill. Sport Books Publisher