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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

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**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?

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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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**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

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**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.

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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)? Ff = 0.03 x 97 x 9.81 = N

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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 = 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

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**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)

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**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.

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**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

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