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

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athlete or machine www raeng org uk athleteormachine

Athlete or Machine?www.raeng.org.uk/athleteormachine

Presented by Dominic Nolan. Education Programme Manager. The Royal Academy of Engineering

slide2
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?

slide3

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
slide4

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
slide5

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
slide6

Gravity (g) = 9.81 m/s2

Max speed if all PE transferred into KE

(diagram not to scale)

Mass (m) of athlete and sled = 97kg

1450m

Vertical drop of track (h) = 152m

Amy Williams max speed

Energy transfer

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 J

Why isn’t the all of the athlete’s and sled’s potential energy transferred into kinetic energy?

slide7

Which two forces resist the forward movement of the athlete and sled down the track?

friction

aerodynamic drag (air resistance)

slide8

Friction force

Friction is a force that resists the movement of two surfaces against each other.

Which combinations provide a lot or a little friction?

rubber / concrete

felt / wood

rubber / rubber

steel / ice

steel / wood

A little friction

A lot of friction

rubber / rubber (1.16)

steel / ice (0.03)

rubber / concrete (1.02)

steel / wood (0.2 - 0.6)

felt / wood (0.22)

slide9

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)?

slide10

CD = 0.42

CD = 1.05

CD = 0.47

CD = 0.5

Aerodynamic drag force

The resistance provided by the air passing over a shape is a force called aerodynamic drag.

Which shapes have a higher or lower coefficient of drag?

Lower CD

Higher CD

slide11

Calculating drag force

  • FDRAG = ½ x  x CDx Afx 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?

slide12

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.

88.56N

80

70

60

50

Force in Newtons (N)

40

30

20

10

0

25

30

35

40

45

5

10

15

20

Speed in metres/second (m/s)

slide13

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: 0.139 m2

ATHLETE 2

Total mass: 100 kg

Af: 0.129 m2

slide14

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