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Lecture Week 2
Linear Kinematics
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EDU4SBM Sports Biomechanics
Linear Kinematics
Linear kinematics describes motion without regards to the force
producing the motion.
Usain Bolt 100 metres 9.69
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EDU4SBM Sports Biomechanics
Displacement
Displacement occurs when a body changes its position.
Displacement
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0
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Time
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EDU4SBM Sports Biomechanics
Velocity
Average velocity is the rate of change of a body’s position with
respect to time.
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Velocity
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10.00
8.00
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4.00
2.00
0.00
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Time
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EDU4SBM Sports Biomechanics
Distance and displacement
Distance
Displacement
e.g. in a 400m race on a track the length of the path the athlete follows (distance) is
400m but their displacement will be zero metres (they finish where they start).
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EDU4SBM Sports Biomechanics
Speed and velocity
Speed of a body is obtained by dividing the distance by the time taken
Velocity is obtained by dividing the displacement by the time taken
e.g. consider a swimmer in a 50m race in a 25m length pool who completes the race in 60
seconds
-distance is 50m and displacement is 0m (swimmer is back where they started)
Speed
= distance/time
Velocity =
displacement/time
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EDU4SBM Sports Biomechanics
Acceleration
Average acceleration is the average rate of change of a bodies velocity
with respect to time.
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Acceleration
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3
2
1
0
-1 0
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-2
Time
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EDU4SBM Sports Biomechanics
Question:
Find the acceleration of a runner starting of with a velocity of zero
(v1=0) and ending up with a velocity of 10 m/s (v2 = 10). This
occurs in 5 seconds.
Acceleration
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EDU4SBM Sports Biomechanics
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Velocity
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Ben 1988
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Carl 1988
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Asafa 2005
Bolt 08
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100
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0
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Displacement
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EDU4SBM Sports Biomechanics
Acceleration
Acceleration is defined as the rate at which velocity
changes with respect to time.
average acceleration = (final velocity - initial velocity) ÷
elapsed time
Acceleration due to gravity
Whilst a body is in the air it is subject to a downward
acceleration, due to gravity, of approximately 9.81m/s²
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EDU4SBM Sports Biomechanics
One of the most famous stories in science is about Galilo and
the Leaning Tower of Pisa. Galileo supposedly reached out
from an upper balcony and let fall two stones of different
weights. A remarkable thing happened: to the gasps and
amazement of the crowd below, the stones hit the ground
together.
Air resistance: stops an object accelerating forever
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EDU4SBM Sports Biomechanics
A cricket ball that has a mass of 0.2 kg has the same mass wherever it is ?
Look at 3 different scenarios:
1) In Bendigo ?
2) On top of Mount Everest ?
3) On outer space ?
Explain.
The weight of a cricket ball is the same wherever it is ?
Look at 3 different scenarios:
1) In Bendigo ?
2) On top of Mount Everest ?
3) On outerspace ?
Explain.
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EDU4SBM Sports Biomechanics
Mass: the quantity of matter of which a body is composed of - not affected by
gravity - measured in kilograms (kg)
Weight: force due to gravity - is mass x gravity (9.81m/s²)
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EDU4SBM Sports Biomechanics
Conclusion
All the principles of movement are based on how forces are made by the athlete or how
they act on the athlete's body.
They may appear complex at first but, as you learn the basics for each event,
biomechanics and an analysis of movement will become an understandable and usable
part of your coaching knowledge helping to make you a better coach.
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EDU4SBM Sports Biomechanics