Athlete or Machine? raeng.uk/athleteormachine

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

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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? - PowerPoint PPT Presentation

Transcript of Athlete or Machine? raeng.uk/athleteormachine

Page 1: Athlete or Machine? raeng.uk/athleteormachine

Athlete or Machine?

www.raeng.org.uk/athleteormachine

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

Page 2: Athlete or Machine? raeng.uk/athleteormachine

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?

Page 3: Athlete or Machine? raeng.uk/athleteormachine

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

Page 4: Athlete or Machine? raeng.uk/athleteormachine

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

Page 5: Athlete or Machine? raeng.uk/athleteormachine

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

Page 6: Athlete or Machine? raeng.uk/athleteormachine

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?

Page 7: Athlete or Machine? raeng.uk/athleteormachine

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

friction

aerodynamic drag (air resistance)

Page 8: Athlete or Machine? raeng.uk/athleteormachine

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?

A lot of frictionA little friction

rubber / rubber (1.16)

rubber / concrete (1.02)

steel / wood (0.2 - 0.6)

felt / wood (0.22)

steel / ice (0.03)

rubber / concrete

felt / wood

rubber / rubber

steel / ice

steel / wood

Page 9: Athlete or Machine? raeng.uk/athleteormachine

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)?

Page 10: Athlete or Machine? raeng.uk/athleteormachine

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?

Higher CDLower CD

CD = 1.05

CD = 0.5CD = 0.47

CD = 0.42

Page 11: Athlete or Machine? raeng.uk/athleteormachine

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?

Page 12: Athlete or Machine? raeng.uk/athleteormachine

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

)

88.56N

Page 13: Athlete or Machine? raeng.uk/athleteormachine

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

Page 14: Athlete or Machine? raeng.uk/athleteormachine

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