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1022 (29/09/20)

Kinematics
Kinesiology – the study of human movement
Kinematics – the description of motion
• Distance and displacement
• Speed and velocity
Kinetics – the forces that cause or tend to cause motion

•
•

Acceleration
The relationships between them

Vectors and scalars
Scalars – magnitude e
...
distance and speed
Vectors – magnitude and direction e
...
displacement and velocity (represented graphically with arrows)

Velocity = 5ms-1

Velocity = 15ms-1

Distance and displacement
Used to describe the motion of bodies
Distance – length of the path followed (m)
Displacement – distance and direction, distance between start point and end point (m)
Distance = 10m

Displacement = 10m

Distance = 10m
Displacement = 0m

Speed and velocity
Speed – calculated by looking at how long it takes an object to cover a certain distance, meaning since
distance is a scalar, speed is also a scalar value
Velocity (ms-1) – calculated by determining how large the displacement change was in a given time,
meaning velocity is a vector so has a magnitude and a direction
Time – measured in milliseconds (ms), seconds (s), minutes (min) or hours (h)
Speed (ms-1) – distance over time taken
...
Velocity = Δd/Δt

1022 (29/09/20)
During training, a player runs the 100m length of a football pitch in 20s, stops for 10s and jogs back in 35s
...
86ms-1

0

10
0

0

20

30

65

Displacement-time graph
Displacement (m)

Velocity = displacement/time
=-100/35
=-2
...
Acceleration = Δv/Δt

1022 (29/09/20)
100m record – Usain Bolt, 2009: 9
...
58
=10
...
Some form of displacement, velocity and acceleration time-profile is required
Displacement-time graph

Race time only allows calculation of average velocity over the entire 100m distance
...
1m split times allow calculation of average velocity
for each 1m interval
Average velocity-time graph
These calculations give an average velocity
between the time points giving a
theoretical value
...
The point in
time for this theoretical value needs to be
considered i
...
when it occurs

Calculating velocity
As the time period between the successive position measures decreases, so the calculated average velocity
becomes more representative of the actual velocity at any instant between those points

1022 (29/09/20)
Instantaneous velocity – the velocity of a body at a specified instant in time
...

• If the data points are close enough together then they can be numerically differentiated to
estimate the instantaneous velocity
• This uses the same method as calculating average velocity just over small time periods

Estimating instantaneous velocity

Application
Measuring kinematics during sport can identify performance aspects – velocity and acceleration profiles,
velocity maintenance and fatigue
General body motion kinematic analysis can identify performance and/or areas for improvement
Errors in kinematic data
• The difference between a measured value and the true value is referred to as the measurement
error/inaccuracy
• No matter how carefully the displacement of the body is measured, there will always be some
measurement error
• Unfortunately, even small errors in displacement data will be magnified when numerically
differentiated to calculate velocity and acceleration
Instantaneous acceleration – calculated in the same way as instantaneous velocity, using numerical
differentiation

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