biomechanics

• Drag force


  A force that acts in opposition to motion
• Streamlining


  Involved shaping a body so it can move effectively and quickly through a fluid
• Lift force


  Causes a body to move perpendicular to the direction of travel
• Bernoulli's principle


  Where air molecules exert less pressure the faster they travel and more pressure when they travel slower
• Angle of attack


  Tilt of a projectile relative to the air flow
• Fluid mechanics is the study of any object or the human body that travels through any liquid or gas and how forces affect them
• Fluid dynamics is a branch of fluid mechanics. Drag and lift are dynamic fluid forces which have an effect on a variety of sports e.g., cycling, sprinting and also swimming
• Any projectile such as a ball, discuss or javelin will also experience drag and lift forces
• Drag


  A dynamic fluid force that is the resistance force caused by the motion of a body travelling through a fluid, slowing it down
• A drag force acts in opposition to the direction of motion and therefore has a negative effect on velocity
• A drag force is produced from air resistance and friction
• Types of drag


  • Surface drag
  • Form drag
• Surface drag

  Relates to friction between the surface of the object and the fluid environment. Its sometimes called skin drag
• Form drag

  Relates to the impact of the fluid environment on an object. Its sometimes called shape drag
• The forces affecting the leading edge of an object increase form drag, and the forces affecting the trailing edge reduce form drag
• Form drag relates to streamlining - a swimmer, has to create the thinnest and straightest form as they move through the water
• A large form drag also offers less turbulent air for anything that is following it - slipstream
• In cycling a cyclist will use another riders slipstream (known as drafting) as the wind hits the first cyclist it goes around the sides and the cyclist behind uses the air pocket that has been created
• To work the cyclist must ride very close (15-30cm) to the bike in front and they can save up to 30% more energy
• Factors that increase & decrease drag

  • The velocity of a moving body
  • The cross-sectional area of a moving body
  • The shape and characteristics of a moving body
• The greater the velocity of a body through a fluid, the greater the drag force
• A large cross-sectional area increases drag
• A more streamlined aerodynamic shape reduces drag
• Sports scientists are regularly trialling drag resistant clothing to achieve 'marginal gains' in speed, to give competitors the edge over their opposition
• The shape and surface of a badminton shuttlecock result in a much larger drag force from air resistance - its unusual shape with feathers and it is light - larger drag force from air resistance means it looses speed quickly
• When a discuss is thrown it experiences an upward lift force during flight. A lift force enables the discuss to stay in the air for longer, therefore increasing the horizontal distance it travels
• Angle of attack


  The tilt of a projectile relative to the air flow
• The angle of attack changes the flow of air around the discuss, so that air travels over the top of the discus has to travel a longer distance than the air underneath
• This results in the air above the discuss travelling at a faster velocity which creates a lower pressure
• This lower pressure above the discuss creates an upward lift force and allows the discuss to stay in the air for longer, resulting in a greater horizontal distance
• If the angle of attack is too great lift is reduced and drag increases, causing the discuss to stall
• The optimum angle attack that produces the best lift for the discuss is anything between 25-40 degrees (release height is above landing height)
• A lift force does not always have to work in an upwards direction. Bernoulli's principle can also be used to describe a downward lift force, such as that required by sports cars, cyclists, and speed skiers
• The car, bike and skis need to be pushed down into the ground, so greater frictional force is created
• In a formula 1 sports car the spoiler is angled to the lift force can act downwards to push the car into the track
• This happens because the air that travels over the top of the car travels a shorter distance than the air underneath due to the angle of the spoiler
• As a result the air above the car travels at slower velocity and a high pressure creates a downward lift force and therefore a greater frictional force, so the tyres maintain a firm grip on the track as the car travels at high speed and around corners
• The cyclist's low streamlined body position over the handle bars means the air that travels over the top of the cyclist has to travel a shorter distance than the air underneath, resulting in the air above the cyclist travelling at lower velocity which therefore creates a higher pressure
• This higher pressure above the cyclist creates a downward lift force and allows the tyres of the bike to maintain a firm grip on the track
• Speed skiers need to stay in contact with the ice for faster speed because more downward lift means more force which melts the ice for a better friction-free surface