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Unit 7. Assignment 1. Linear Motion in Sport and Exercise Activities.
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Unit 7. Assignment 1. Linear Motion in Sport and Exercise ActivitiesI have been asked by my college athletics coach to help to improve the performance of some of the
performers in athletics. The coach is concerned with a 100m sprinter (Yohan Blake) and a 400m runner
(Asafa Powell) in relation to their speed and acceleration on the track. The coach has asked me to
investigate factors related to linear motion for these athletes to see which areas of their performance
could be improved upon. I will need to assess these athletes' speed, velocity, acceleration, deceleration,
and momentum during drills and in competition.
Speed & Velocity:
Speed can be defined as the rate of change in distance i.e., Speed (ms -1) = Distance (m)/ Time (s) and is a
scalar quantity (Walden, 2022). Speed is a scalar quantity because it only has a magnitude (Why Speed Is
a Scalar?, 2022). Velocity is the rate of change of displacement i.e., Velocity (m/s) = Displacement (m)/
Time (s) or the speed of a body moving in a certain direction. In contrast to speed, velocity is a vector
quantity, meaning it has both a direction and a magnitude. Therefore, even if the speed may not vary,
the velocity will change if the direction of the moving body changes (Walden, 2022). For example, if a
sprinter runs in a straight line, distance and displacement are equal, making speed and velocity equal.
However, if a sprinter runs along a bend, distance and displacement are not equal, making speed and
velocity different values.
Acceleration & Deceleration:
The rate at which a body increases its velocity is known as its acceleration i.e., Acceleration (m/s/s or ms -
2
) = Change in Velocity (m/s)/ Time (s). Like velocity, acceleration is a vector quantity, meaning it has
both a direction and a magnitude (Walden, 2022). To calculate acceleration, you take the final velocity
(Vf) and subtract it by initial velocity (V i) and divide this number by time. Because external forces (e.g.,
ground forces against foot strides of a sprinter) can cause a body to accelerate, acceleration is directly
proportional to the force; hence acceleration can also be expressed as Acceleration (ms -2) = Force (N)/
mass (kg). Deceleration (a vector quantity) is when the initial velocity (V i) is greater than the final
velocity (Vf), representing a body that is slowing down over time due to acceleration that occurs in the
direction that is opposite to the velocity (e.g., air resistance or traction on a sprinter) (Hamm, 2020).
Deceleration may also be calculated as change in speed over a period of time by using formula final
velocity (Vf) minus initial velocity (Vi) divided by the time taken for the drop in velocity (t)
Momentum:
Momentum (a vector quantity) is a measure of the amount of motion a body has i.e., Momentum
(Kgm/s) = Mass (Kg) x Velocity (m/s) (Walden, 2021). Momentum’s formula however is written as
Momentum (p) = Mass (m) x Velocity (v) and can be useful for coaches to calculate how much inertia
sprinters need to overcome to achieve certain speeds during a race. This also allows coaches to see if
their sprinters’ bodyweights are optimal for their sprint performance, and/or power to weight ratio. For
sprint events with bends (e.g., 200m, 400m), momentum could be used to see the difficulty sprinters
may experience when changing velocity to run along bends (because the change in direction results in
changing velocity, so the sprinter will experience changing momentum). Again, momentum is a vector
quantity as it is mass and velocity, and velocity has a magnitude and direction, meaning that momentum
has a magnitude and direction.
, Linear Motion and types of linear motion:
Linear motion:
A body is said to be in linear motion when it moves along a line (either straight or curved) in a plane
(GeeksforGeeks, 2022).
Curvilinear motion:
Curvilinear motion is motion in which a body's trajectory follows a curved line and its direction of
velocity is varied (Curvilinear Motion, n.d.).
Rectilinear motion:
Rectilinear motion is characterised as a phenomenon when a body only moves in a straight path
(GeeksforGeeks, 2022).
Yohan Blake (100m):
Blake completed the 100 metres in 9.69 seconds on August 23, 2012, at the Athletissima Diamond
League competition in Lausanne, Switzerland. In the 100m sprint, there are different established phases
which are the drive phase, 30-50m phase, and the 50-100m phase (Sladden, 2021). These phases will be
used to analyse Yohan Blake’s performance. As the 100m is straight, the linear motion that Blake runs
the race in is rectilinear motion because the path that Blake runs is straight. During this race, Blake
completed the drive phase (0-30m) in 3.56 seconds. This would give Yohan Blake an average speed and
velocity of 8.43 m/s (30m–0m/3.56s). In this instance, both speed and velocity can be used because
Blake is moving in a linear direction, meaning that his total distance and displacement for the whole race
will be equal, hence why speed is equal to velocity in this race. In this phase of the race, Blake will have
the lowest speed/velocity because he must generate force to accelerate up to maximum speed/velocity.
During this phase, Blake had an average acceleration of 2.37 m/s 2 (8.43 m/s – 0 m/s /3.56s) the greatest
accelerative phase of the race due to his initial velocity being 0 m/s, making it impossible for Blake to
equal or exceed the same acceleration as this would greatly exceed his maximum or terminal
speed/velocity. For Blake to improve his performance during the drive phase, greater acceleration
would be required to enable Blake to achieve higher speeds/velocities over the same distance,
increasing his chance of winning and breaking a record. In the drive phase, Blake has an average
momentum of 674.16 kgm/s [80kg (Yohan Blake Bio, Stats, and Results, n.d.) x 8.43 m/s]. As Blake’s
body mass is a fixed value (during the race), for Blake to increase his momentum, he would need to
increase the linear force he produces to increase acceleration as Force (N) = Mass (kg) x Acceleration
(m/s2). For Blake to increase his momentum, he would need to increase his velocity as mass is fixed
during the race. However, if the same momentum were achieved with a lower body mass, this would
still represent an increase in sprint velocity, helping Blake win and achieve records, because if mass
decreases, velocity will have to increase to maintain the same momentum.
Blake completed the next 20m (30-50m) in 2.08 seconds. This would give Yohan Blake an average speed
and velocity of 9.62 m/s (20m/2.08s). As Blake’s velocity is still increasing and was 8.43 m/s at 30m, his
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