Download air or water

KEY KNOWLEDGE
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Projectile motion of the
human body and objects
through the air and
through water
Key principles associated
with projectile motionof
objects including lift, the
Magnus effect, spin,
height and angle of
release, velocity of
release, angle of
projection and flight path.
© Cengage Learning Australia 2011
KEY SKILLS
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Correct use of terminology to explain how
biomechanical principles apply to a range of
sports actions
Describe how spin can be used to bring about
successful performances in sport such as swing,
lift and turn
Participate in, analyse and report on a range of
practical activities that consider biomechanical
principles
Use biomechanical principles to critique the
effectiveness of different movements
Analyse different sporting actions to identify
similarities and differences as well as the correct
application of biomechanical principles to
improve performance
© Cengage Learning Australia 2011
Projectile motion
Anything launched into the air (only influenced by
gravity and air resistance) has a projectile motion.
Projectiles have both a vertical and horizontal
component.
The vertical component is influenced by gravity
and force of projection.
The horizontal component is influenced by air resistance
© Cengage Learning Australia 2011
Factors affecting flight path
of a projectile
• angle of projection / release
• speed of projection / release
• height of projection / release.
© Cengage Learning Australia 2011
Angle of projection
This is the angle
at which an object
is released into
the air.
© Cengage Learning Australia 2011
© Cengage Learning Australia 2011
Speed of release
This is influenced by the vertical component which determines the
height reached and the flight time of an object, and the horizontal
component / force, which determines the horizontal distance
covered by the object.
© Cengage Learning Australia 2011
Height of release
This is calculated by subtracting the height
that the projectile is released, from the
height at which it stops/ ends.
If height of release is 0° (projection height
and landing height are both equal)
optimal angle of release = 45°.
If height of release is greater than 0°
(projection height is above landing height)
optimal angle of release = less than 45°.
If height of release is less than 0°
(projection height is below landing height)
optimal angle of release = greater than
45°.
© Cengage Learning Australia 2011
Human movement through air and water
Laminar and turbulent flow
When objects move through air or water slowly they do not
disturb the flow a great deal and the air or water will flow in a
smooth, parallel manner around the object = laminar flow.
When objects move through air or water rapidly they disturb the flow to the point
that layers next to the surface of the object get mixed together = turbulent flow
© Cengage Learning Australia 2011
Buoyancy
This is upwards force acting on a body
within water.
The buoyant force = weight of fluid
displaced by an object.
The greater density a fluid has, the more
buoyant objects will be when placed in this
medium.
When buoyancy force and weight are equal
and object will float, but when weight of an
object is greater than the buoyancy force, it
will sink.
© Cengage Learning Australia 2011
Drag force
Is created when an object moves through a fluid or when fluid flows around
a stationary object.
In air the drag force is known as air resistance
In water the drag force is known as hydrodynamic resistance
Bernoulli’s Principle explains how as the
velocity of fluid increases, the pressure
decreases. This causes an area of
turbulence behind the object where
pressure is less than in front of the object.
Forces will always act from the area of
high pressure to an area of low pressure.
Streamlining decreases turbulence created
at the back of an object and thus
reduces drag.
© Cengage Learning Australia 2011
Drag is affected by the following factors:
•the shape of an object and how streamlined it is
•the density of the fluid (air or water)
•the velocity of the object as it moves through the
fluid
•the cross sectional area of the object in the
direction of the motion.
© Cengage Learning Australia 2011
Lift force acts perpendicular to the flow of the fluid and is affected by:
• the velocity of the fluid
• the density of the fluid
• the size, shape and position of the object
• the foil shape
• angle of object relative to direction of flow
• the Magnus effect
• uneven surface coatings.
A foil has a curved and a flat surface
which causes fluid to flow faster over
the curved surface than the flat one,
leading to pressure differences.
Lift force is generated from the area of high pressure to
the area of low pressure.
© Cengage Learning Australia 2011
Angle of attack
This is the angle between the long axis of the object and the direction
of air / water flow.
A positive angle of attack is required to create lift force
© Cengage Learning Australia 2011
The Magnus effect
Lift can be created by spin (topspin, backspin and sidespin) and the
deviation towards the direction of spin is knows as the Magnus effect. A lift
force will act from the area of high pressure to the area of low pressure.
© Cengage Learning Australia 2011
© Cengage Learning Australia 2011
Surface differences
• Air will travel across a smooth surface quicker than over a rough surface.
• Turbulent air from the rough surface is at lower pressure than air flowing over
the smoother surface which is at higher pressures.
• This causes a pressure difference, and lift force is towards the side with lower
pressure.
© Cengage Learning Australia 2011