Year 9 STEM Club The Skeleton Luge. CHALLENGE Make a model of a bob skeleton sled See how far you can launch a Barbie! Present an answer to the question:

Year 9 STEM Club

The Skeleton Luge

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?

http://www.youtube.com/watch?v=rwOTbxO44j8

Session plans

• Week 1 – Intro and start building

• Week 2 – Finish building and test

• Week 3 – Competition – Distance and Speed

• Week 4 – Athlete or Machine?

Week 1 • Introduction to the task

• Video

• Meet Barbie

• Each team given resources and drilling template

• Start building

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

Drilling template

Week 2 • Continue to build

• Start testing the launch

• Redesigns and refinements

Launch the model bob skeleton sled.

Launch Barbie!

Week 3 • Competition time

• Distance with and without Barbie

• Speed with and without Barbie

• Timing gates

Extension

Set up timing gates to measure the speed of the sled with and without the Barbie.

What factors are going to affect the speed at which Barbie travels?

What factors are going to affect the speed of the real Skeleton Luge on an ice track?

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

Week 4 • Athlete vs Machine

• Use calculations to work out which element of the luge/athlete partnership is the most influential to its success.

• Summary and extension

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

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?

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)?

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?

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

)

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

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

Summary and Extension