CQ3 – How do biomechanical principles influence movement? PRELIMINARY HSC PDHPE CQ3 – How do biomechanical principles influence movement?

How do biomechanical principles influence movement? Students learn about: motion the application of linear motion, velocity, speed, acceleration, momentum in movement and performance contexts Students learn to: apply principles of motion to enhance performance through participation in practical workshops balance and stability centre of gravity line of gravity base of support apply principles of balance and stability to enhance performance through participation in practical workshops fluid mechanics flotation, centre of buoyancy fluid resistance   apply principles of fluid mechanics to enhance performance through participation in practical workshops describe how principles of fluid mechanics have influenced changes in movement and performance, eg technique modification, clothing/suits, equipment/apparatus force how the body applies force how the body absorbs force applying force to an object. apply principles of force to enhance performance through participation in practical workshops.

Fluid mechanics Fluid mechanics refers to forces that operate in water and air environments. These forces will affect how well we can move through the water (either in a vessel or as a swimmer) or how we can move ourselves or projectiles through the air. Two important forces influence our ability to perform effectively in a water environment: buoyant force and drag force.

flotation, centre of buoyancy Two forces operate on a body in a fluid environment to determine its buoyancy (ability to float). These forces are the buoyant force that pushes the body up and the weight force that pulls the body down (gravity). Archimedes’ Principle states that a body that is partially or totally immersed in a fluid will experience buoyancy that is equal to the weight of the volume of fluid displaced by that body. So, if the buoyant force is greater than the weight force, the body will float. Conversely, if the buoyant force is less than the weight force, the body will sink.

flotation, centre of buoyancy

fluid resistance Fluid resistance Forces act on us when we attempt to propel ourselves through a fluid environment. These forces include drag force and lift force. Elite athletes understand and use these forces in a way that will benefit the efficiency of their performance.

Drag Drag force is sometimes referred to as resistance, and is the resistance that acts against a body as it moves through a fluid environment. Friction occurs when one body (for example, a hand or oar) moves across the surface of another (for example, water). Friction will always oppose motion. A difference in pressure occurs to the opposing sides of the body in the water and this acts to propel the body forward. When swimming, a low-pressure area is created in front of the hand and a corresponding high-pressure area forms behind the hand. As the hand pushes the water back, the drag forces propel the body forward (see Figure 6.13). Fast swimmers or paddlers create a greater pressure differential by utilising skills such as streamlining and pitching the entry of their hands to ensure the water surface is cut cleanly. This prevents air bubbles from being trapped or dragged through the water.

Lift Lift force is often referred to as hydrodynamic lift force when created in the water. It is much greater than that lift created in air, as water is denser. This force occurs perpendicular to the flow of the water over the body when swimming. When performing an eggbeater kick in water polo (see Figure 6.14), hydrodynamic lift force is created as the legs alternately circle under the water creating pressure differences between the top and bottom of the leg and foot. The lift force acts to push the athlete upwards. Swimmers experience a lift force as they stroke the water, as the flow of water over the hands creates a forward lift force that is equal to the force exerted by the swimmer, thus pushing the athlete to the surface.

The Magnus effect The Magnus effect (see Figure 6.15) occurs when a spinning object creates a whirlpool of rotating air or liquid around it. Velocity increases on one side of the object, where the fluid travels in the same direction as the whirlpool. As the velocity of a fluid increases, the pressure exerted by the fluid will decrease. The opposite side of the object experiences decreased velocity as the motion of the whirlpool is reversed. This creates spin and makes it difficult for an opponent to read the direction of flight and respond accordingly

The Magnus effect

How the principles of fluid mechanics have influenced performance In our technological age, the study of the principles of fluid mechanics has influenced the performances of our elite athletes. This knowledge has influenced the design of performance clothing, equipment and the environments in which competition takes place. Much controversy has surrounded the use of ‘fast skin’ swimsuits, especially in view of the number of world records that has fallen since their inception. The revolutionary design resulted in decreased drag and increased buoyancy for the athlete and, as results have proven, unprecedented improvement in performance at the elite level of swimming. Following the 2008 Olympic Games, the international swimming body, FINA, investigated the use of high-tech suits and has placed regulations on their use to ensure no unfair advantage is gained through the use of technology.

How the principles of fluid mechanics have influenced performance The training focus at elite level also evolved to see athletes spend as much as 50 per cent of their time in the pool refining the technical aspects of kicking, pulling, breathing and body position in an attempt to reduce drag and maximise the lift force to produce more efficient movement. The advent of video- analysis of stroke count, splits, turns and take-offs has resulted in athletes developing a better understanding of the relationship between the acting forces and their personal performance.

How the principles of fluid mechanics have influenced performance Equipment and the racing environment have also changed to counteract the negative effects of fluid mechanics. Olympic pools are now 10 lanes wide, keeping the two outside lanes free. Pool edges feature gutters that are flush with the water surface. Plastic buoys that divide lanes are designed to direct water downward and not outward. These modifications stop excessive wave motion.

Revision/Homework task Answer/complete the following statements/questions: describe how principles of fluid mechanics have influenced changes in movement and performance, eg technique modification, clothing/suits, equipment/apparatus