1. Athlete or Machine? www.raeng.org.uk/athleteormachine
Presented by Dominic Nolan. The Royal Academy of Engineering

2. 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

3. Make a 1:5 bob skeleton sled
90 minute make
Cheap materials
Basic tools and equipment

4. Make a launcher

5. Make some timing gates (if you have the time)
Achieving launch pressure consistency

6. 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

7. Which is more important in the sport of bob skeleton?
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?

8. 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

9. Launch the model bob skeleton sled.
Launch Barbie!

10. Factors Weight 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

12. Potential Energy (PE) = m x g x h Kinetic Energy (KE) = ½ x m x v2
Energy transfer
Potential Energy (PE) = m x g x h
Change in PE for our athlete and sled =
Joules (J)
Kinetic Energy (KE) = ½ x m x v2
0.5 x 97 kg x (40.23 x 40.23) = J
Mass (m) of athlete and sled = 97kg
Vertical drop of track (h) = 152m
1450m
(diagram not to scale)
Gravity (g) = 9.81 m/s2
Amy Williams max speed
Max speed if all PE transferred into KE
Why isn’t the all of the athlete’s and sled’s potential energy transferred into kinetic energy?
The line graph above shows that if all the potential energy (PE) were to be transformed into kinetic energy (KE) then the athlete and sled would need to travel at 55 m/s (122 miles per hour) to reach a KE figure of J.
However, the 2010 bob skeleton Olympic champion, Amy Williams, is known to travel at a maximum speed of 90 mph (40.23 m/s).
Our simple analysis of the energy transfer over estimates the maximum speed of the athlete and sled by 15 m/s or 37% because it neglects the affects of aerodynamic drag and friction.

13. 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)?
Ff = 0.03 x 97 x 9.81 = N

14. 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 = 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?
FDRAG = 0.5 x 1.2 x 0.45 x x 1600 = N

15. Speed in metres/second (m/s) Speed in metres/second (m/s)
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 20 30 40 50 60 70 80 5 15 25 35 45
Speed in metres/second (m/s)
Force in Newtons (N)
F TOTAL = N 10 20 30 40 50 60 70 80 5 15 25 35 45
Speed in metres/second (m/s)
Force in Newtons (N)

16. Prove that it is better to be heavy and narrow when competing in
The sport of bob skeleton.
ATHLETE 1
Total mass: 97 kg
Af: m2
ATHLETE 2
Total mass: 100 kg
Af: m2
ATHLETE 1
Friction force = 0.03 x 97 x 9.81
Friction force = N
Drag force = 0.5 x 1.2 x 0.45 x x 1600
Drag force = N
Total force acting against athlete and sled = N
ATHLETE 2
Friction force = 0.03 x 100 x 9.81
Friction force = N
Drag force = 0.5 x 1.2 x 0.45 x x 1600
Drag force = N
Total force acting against athlete and sled = N
Athlete 2 should get to the bottom of the track quicker as there is less force acting against the forward motion of the athlete and sled.
Increasing athlete mass does not have a significant impact on friction compared to effect of increasing frontal area.

17. Which is more important in the sport of bob skeleton?
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