Transcript Quantitative Biomechanics - CCVI

Quantitative Biomechanics
Distance vs Change in Position
• Distance is the path that an object has
travelled
• Ex. The distance around a track is 400m
• Position is the straight line measurement from
the starting position to the ending position
• Ex. The change in position around a track is
0m
Speed vs Velocity
• Speed is the rate of change of distance
• Velocity is the rate of change of position
• Speed and Velocity in a straight line are the
same. Speed and Velocity over a curved path
will be different.
Velocity
• Velocity is the rate of change of position
• V=(p2-p1)/(t2-t1)
• Direction can be included as + or –
– Up and Right are position
– Down and Left are negative
– Be sure about direction if you are using it in various
movements skills as the direction may not be clear
– In this case you do not need to include direction in
this way but just in a manner that makes it clear
Acceleration
• Acceleration is the rate of change of velocity
• a = (v2-v1)/(t2-t1)
• Acceleration can be positive (speeding up) or
negative (slowing down)
• Remember that if mass of an object is
consistent then Force and Acceleration are
proportional due to F=ma
Force, mass, and acceleration
The greater the force applied to a soccer ball that has the
same mass, the greater the ball’s acceleration
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Force, mass, and acceleration cont.
As the soccer ball’s mass increases, it experiences
less acceleration from a kick of the same force
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Force, mass, and acceleration cont.
As the mass of the soccer ball is increased, greater
force must be generated if the ball is to have the
same acceleration
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Graphing
• Position-Time Graphs
– Show velocity
• Velocity-Time Graphs
– Show acceleration
Graphical analysis of motion
• (i) at rest
• (ii) moving with uniform speed
displacement
0
Time
Graphs
moving with non-uniform speed
Displacement
minimum speed (at
rest)
maximum speed
Increasing speed
0
Time
Graphical Representations
(i) at rest
(ii) moving with uniform speed
(iii) moving with uniform acceleration
(iv) moving with non-uniform acceleration
Velocity
(ii)
(iii)
(iv)
(i)
Time
Other skills that could be useful
– To calculate the area under a speed-time graph to
determine the distance travelled for motion with
uniform speed or uniform acceleration
– The acceleration of free fall for a body near to the
Earth is constant and is approximately 10 m/s2
Area Under the Curve of a Graph
A bus stopped at a bus-stop for 10 seconds
before accelerating to a velocity of 15 m/s
in 4 seconds and then at a constant speed
for the next 9 seconds. How does the graph
look like?
Velocity /m/s
(ii)
15
(iii)
(i)
0
10
14
23
Time/s
Area Under A Graph
A bus stopped at a bus-stop for 10 seconds
before accelerating to a velocity of 15 m/s
in 4 seconds and then at a constant speed
for the next 9 seconds.
Velocity /m/s
(ii)
15
(iii)
(i)
0
10
14
23
Time/s
Area Under A Graph
A bus stopped at a bus-stop for 10 seconds
before accelerating to a velocity of 15 m/s
in 4 seconds and then at a constant speed
for the next 9 seconds.
Velocity /m/s
(ii)
15
How far did the
bus go in this 23
seconds?
(iii)
(i)
0
10
14
23
Time/s
Why is all this helpful
• Sometimes your eyes can trick you
• Explains how changes in force happen
• The difference between the best and worst
players many times is the speed at which
movements are done
What do you need to know
• How to calculate :
– Speed
– Change in position
– Velocity
– Acceleration
• How to read graphs showing changes in:
– Position
– Velocity