Biomechanical Principles of Motion through air and water By Lauren Borg and Tiffany Marygold

The two mediums that us as humans generally perform in are air and water. They are both fluids and so both exert forces on the body as it moves through. When an object or body travels through the air, it is considered projectile and its flight path is determined by a number of factors.

Projectile motion! Contents Vertical and horizontal components Factors affecting the path of a projectile Factors that may influence projectile motion Angle of projection Speed of release Height of release

Anything that travels through the air and is affected by the forces of gravity and air resistance is considered as a projectile. Projectile motion is the factors that influence the flight path of the projectile.

Vertical and horizontal components Anything that is considered as a projectile will have horizontal and vertical components. This is the easiest way to analyse motion biomechanically.

Vertical component The vertical component of projectile motion is influenced by gravity. Gravity causes objects to accelerate towards the earth at a rate of 9.81 m/s² It is gravity that gives projectiles the parabolic flight path. (figure 5.2) Regardless of size, shape or weight all objects will pick up speed due to gravity.

Horizontal component The horizontal component is affected by air resistance. If there was no air resistance, the horizontal velocity of a projectile would remain the same.

Factors affecting the path of a projectile The path of a projectile can be affected by three factors: Angle of projection (or release) Speed of release (or projection) Height of release (or projection)

Factors that may influence projectile motion Flight time Distance (horizontal) Distance (vertical) Flight path Manipulating these variables helps determine the best combination for optimum performance.

Angle of projection The angle of projection is the angle at which an object is released. This will determine the flight path of the projectile. There are three shapes that a flight path can form.

Vertical trajectory

Oblique trajectory

Horizontal trajectory

Speed of release This is the speed at which an object is released. Projectiles have both a horizontal and vertical component. The vertical component determines the height reached and the flight time of the projectile. The horizontal component determines the distance covered by the projectile.

Height of release This is the difference between the height that a projectile is released and the height at which it lands or stops.

Human movement through air and water Contents Laminar and turbulent flow Buoyancy Drag force Lift force (foil shape, angle of attack, Magnus effect)

Laminar flow When the flow of the fluid is not disturbed much, this is called laminar flow.

Turbulent flow When the layers of fluid near the surface get mixed together, this is called turbulent flow.

Buoyancy Buoyancy is the force that acts vertically upwards on a body that is immersed in water. The buoyant force is equal to the weight of the fluid that has been displaced. Buoyancy is affected by the density of the fluid, this means it is easier to float in the ocean then fresh water as the buoyancy is greater in sea water.

Drag force When a fluid flows around a stationary object or when an object moves through a liquid, drag force is generated. This slows the object down. In air this is called air resistance, and in water this is called hydrodynamic resistance. As the velocity of the fluid increases, the pressure decreases. This is known as Bernoulli’s principle.

Drag is affected by a number of factors: The shape of an object The density of the fluid The cross-sectional area of the object in the direction of motion The velocity of the object

Lift force Lift force is the perpendicular movement to the flow of the fluid. The factors affecting the lift force are similar to those that affect drag: The velocity of the fluid The density of the fluid The size, shape and position of the object or body.

Lift can occur due to: The foil shape The angle of the object relative to the direction of the flow The Magnus effect The unevenness of surface on one side of a ball compared to another.

Foil shape A foil shape is one that can generate lift when in air or water.

Angle of attack The angle of attack is the angle between the long axis of the object or body and the direction of the air or water flow.

Magnus effect A spinning object creates regions of high and low pressures on either side of an object by increasing the fluid on one side and decreasing on the other, generating lift. The pressure difference is called Magnus force, which causes the object to deviate in the direction of the spin. This deviation is known as the Magnus effect.