Transcript Year 9 STEM Club

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?
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)
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
Energy transfer
Potential Energy (PE) = m x g x h
Change in PE for our athlete and sled =
Mass (m) of athlete
and sled = 97kg
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?
Vertical drop of
track (h) = 152m
Gravity (g) = 9.81
m/s2
1450m
(diagram not to scale)
Max speed if all PE
transferred into KE
Amy
Williams
max speed
Calculating friction force
Ff =  x m x g
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 = …………………………
=
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.
Calculating drag force
Calculate the drag force acting on the athlete and
sled as they travel down the track at 40 m/s?
FDRAG = ½ x  x CD x Af x V2
FDRAG = ………………………….
=
CD =
1.2 kg/m3
0.45
(density of air)
(drag coefficient of athlete and sled)
Af =
0.139 m2
(frontal area of athlete and sled)
V =
40 m/s
(velocity)
What is the total force resisting the
forward movement of the athlete and
her sled down the track?
Force in Newtons (N)
FTOTAL = ……………………………………
80
Between which velocities is friction
force dominant?
70
………………………………………………..
60
Between which velocities is drag force
dominant?
50
………………………………………………..
40
You can compare the two forces on the
graph here.
30
20
10
0
5
10
15
20
25
30
35
Speed in metres/second (m/s)
40
45
Prove that it is better to be heavy and narrow when competing in
The sport of bob skeleton.
ATHLETE 1
ATHLETE 2
Total mass: 97 kg
Total mass: 100 kg
Af :
0.139 m2
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