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Athlete or Machine?
www.raeng.org.uk/athleteormachine
Presented by Dominic Nolan. The Royal Academy of Engineering
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Investigate the big question: athlete or machine?•Practical activities and testing
•Mathematics activities
•Science activities
•Engineer/athlete video
•Student led
•Independent investigation
•Higher level thinking
•Scheme of work for STEM day or STEM club
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Make a 1:5 bob skeleton sled
•90 minute make
•Cheap materials
•Basic tools and equipment
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Make a launcher
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Make some timing gates (if you have the time)
Achieving launch pressure consistency
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Bob Skeleton
•1500m track
•150 m vertical drop
•143 km/h (40 m/s, 89 mph)
•Athletes times differ by tenths of seconds
•Rules for sled’s dimensions, mass and materials
•33 – 43 kg sled
•Amy Williams - Olympic gold 2010
•www.youtube.com
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CHALLENGE
•Make a model of a bob skeleton sled
•See how far you can launch a Barbie!
•Present an answer to the question:
Athlete or Machine?
Which is more important in the sport of bob skeleton?
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Make a 1:5 bob skeleton sled
•Make the runners by bending the metal rod
•Attach runners to pod with cable ties
•Make sled’s launch tube using acetate sheet, tape and a plastic nose cone (check that it fits onto the pump’s launch tube)
•Fix the launch tube to the pod with double-sided sticky pads
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Launch the model bob skeleton sled.
Launch Barbie!
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FactorsWeight
The athlete’s shape
The athlete’s position
Aerodynamic lift
Steering
Clothing and equipment
Starting
Corners
Ergonomics (how the body fits a product)
Track incline (the slope down the length of the track)
Friction on the ice
Aerodynamic drag (air resistance)
Tuning the characteristics of the skeleton
Material choice
Sled runners
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Potential Energy (PE) = m x g x h
Change in PE for our athlete and sled =
144 639 Joules (J)
Kinetic Energy (KE) = ½ x m x v2
0.5 x 97 kg x (40.23 x 40.23) = 78495 JThe bob skeleton: kinetic energy gained during a run
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
5 10 15 20 25 30 35 40 45 50 55 60
Speed in metres per second (m/s)
Kin
etic
en
erg
y (J
ou
les)
Amy Williams max speed
Max speed if all PE transferred into KE
Mass (m) of athlete and sled = 97kg
Vertical drop of track (h) =
152m
1450m
(diagram not to scale)
Gravity (g) = 9.81 m/s2
Energy transfer
Why isn’t the all of the athlete’s and
sled’s potential energy transferred into
kinetic energy?
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Calculating friction force
Ff = x m x g
Ff = …………………………
= Mu, the coefficient of friction (steel on ice = 0.03).
m = Mass (kg).
g = The acceleration due to the gravity, which is 9.81 m/s2.
What is the friction force acting on the runners of a bob skeleton sled and
athlete with the combined mass of 97 kg (athlete = 68 kg, sled = 29 kg)?
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Calculating drag force
FDRAG = ½ x x CD x Af x V2
FDRAG = ………………………….
= 1.2 kg/m3 (density of air)
CD = 0.45 (drag coefficient of athlete and sled)
Af = 0.139 m2 (frontal area of athlete and sled)
V = 40 m/s (velocity)
Calculate the drag force acting on the athlete and
sled as they travel down the track at 40 m/s?
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What is the total force resisting the
forward movement of the athlete and
her sled down the track?
FTOTAL = ……………………………………
Between which velocities is friction
force dominant?
………………………………………………..
Between which velocities is drag force
dominant?
………………………………………………..
You can compare the two forces on the
graph here.
10
0
20
30
40
50
60
70
80
5 10 15 20 25 30 35 40 45
Speed in metres/second (m/s)
Fo
rce
in
Ne
wto
ns
(N
)
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Prove that it is better to be heavy and narrow when competing inThe sport of bob skeleton.
ATHLETE 1
Total mass: 97 kg
Af: 0.139 m2
ATHLETE 2
Total mass: 100 kg
Af: 0.129 m2
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Athlete or Machine?Which is more important in the sport of bob
skeleton?
•Discuss this question with your partner/team
•Present your answer to the rest of the group
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