Transcript Lect 6 Motion

Linear Motion
•
Movement in a straight line of a
body or body part. (Translatory
motion)
•
The sprinter runs from A to B.
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Curvilinear Motion
•
•
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Movement along a curved line.
Most jumps are along a curved
line.
Projectile Motion
• Motion of an object or person in flight.
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Linear Motion I – Middle Secondary
Introduction to Linear Motion
speed
distance / displacement
velocity
acceleration
Graphical representation
distance - time graphs
speed - time graphs
velocity - graphs
Linear Motion II – Senior Secondary
Non-uniform motion
displacement
velocity
acceleration
instantaneous speed
average speed
Uniform motion
equations for uniform motion
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Many sports involve the throwing of a ball
or other object. This article discusses the
basics of projectile motion, and for ease of
understanding, we will consider that there
is no air resistance. The influence of air
resistance, friction, spin, and air flow
around the object is discussed elsewhere
Any projectile thrown, such as a ball, can
be considered to have a vertical and
horizontal velocity component, as shown in
this diagram (blue=horizontal velocity
component, red=vertical velocity
component).
Throughout the path of the projectile,
change occurs only in the vertical direction
due to the influence of gravity, while the
horizontal component of the velocity will
not change. (This is not quite true, there
will be a very small slowdown in the
horizontal direction due to air resistance).
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Projectile Motion
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There are many examples of projectile motion is sport.
•Golf ball
•Basketballs
•Javelin
•Ski jumping
•Diving
•Trampoline
•Archery
•Soccer
•Football
•Cricket
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The following factors influence the projectiles trajectory

Angle of release

Speed of release

Height of release

Gravity

Spin

Air resistance
See java demo
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Spin
Magnus Effect
When sports players produce curve balls, be it
through throwing, kicking or hitting a ball, they are
exploiting the Magnus effect.
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The Magnus effect causes a spinning ball moving through air (or
any other fluid such as water) to produce a force perpendicular to
both its spin axis and its direction of travel. This force causes the
ball to curve either left or right if the spin axis is vertical. If the spin
axis is both horizontal and perpendicular to its direction of travel
then the ball will either descend faster or slower than it would
otherwise under the influence of gravity alone.
Magnus Effect is a lifting force
produced when a rotating cylinder
produces a pressure differential.
This is the same effect that
makes a baseball curve or a golf
ball slice.
The difference in surface velocity accounts
for a differ-ence in pressure, with the
pressure being lower on the top than the
bottom. This low pressure area produces
an upward force known as the “Magnus
Effect.”
This
mechanically
induced
circulation illustrates the rela-tionship
between circulation and lift.
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Friction
Friction
Friction can be defined as the resistance to motion of two moving
objects or surfaces that touch.
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COR
To find the coefficient of restitution in the case of a falling object
bouncing off the floor, or off a racquet on the floor, use the
following formula:
c = coefficient of restitution (dimensionless)
h = bounce height
H = drop height
The coefficient of restitution (denoted by the symbol c in our formulas)
is a measure of the elasticity of the collision between ball and racquet.
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And the coefficient of restitution merely tells you how much of the original
kinetic energy remains after a collision of the clubhead with the golf ball.
The higher the coefficient of restitution, the faster the ball will be propelled
by the clubhead for a given impact speed.
So why all the fuss over this figure?
It's because the USGA is trying its best to limit the influence of technology
in golf. Theory being that golf should challenge the skill and savvy of the
individual rather than the technology in his or her bag. And this is probably
a good thing for the sport. After all, it would be very effective to go bass
fishing by dropping depth charges over the side of your boat. Just scoop
'em up when they float to the surface. But would that really be bass fishing?
So the USGA has adopted limits of 0.830 on the coefficient of restitution a
given clubface may have as part of its effort to define the boundaries of
technology in the game.
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Projectile Motion
• Motion of an object or person in flight.
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Factors Affecting Pathways
The pathway of an object is determined by:
• The angle of release.
• Drag force is a resistant force
• Lift force
• Type of spin
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• When an athlete launches himself or an object into flight gravity will
act as a force pulling the athlete or object towards the ground. The
flight path of the centre of gravity of a body is a curve called a
parabola. The parabolic flight path depends on three factors:
• ● Speed of take off or release
• ● Angle of take off or release
• ● Height of the athlete's CG at take off, or CG of implement at
release
•
Of these, the speed of an athlete at take off, or of an implement at
release, is the most important factor. Greater speed means greater
distance achieved. Air resistance can also affect the distance
travelled by an athlete or implement.
•
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Drag Force
• Drag force is a resistance force
- a force that slows the motion
of a body through a fluid (air or
water).
• Sportsmen reduce drag by
using specialised techniques,
equipment or clothing.
• Streamlining reduces form drag.
"Photos courtesy of and copyright Free Range Stock,
www.freerangestock.com"
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Lift Force
• Lift force is a force
generated
perpendicular to fluid
flow.
Direction of
fluid flow
Lift force
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Types of Spin
• Spin is the rotation of a body or object.
• Torque is the force which creates spin.
• The type and amount of spin depends on how
much torque is applied and where it is applied.
TOPSPIN
SIDESPIN
BACKSPIN
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Outcome of Spin
• Players learn to control the amount of spin
to achieve different effects.
• Draw diagrams to represent the outcome
the different types of spin.
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