Speed of a Cliff Diver: Iraqi Olympic Diving

The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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Introduction

This is a mechanics problem that a physics student should be able to solve.

Go to http://www.thatwasrandom.com/content/view/110/48/ and watch the Iraqi Olympic Diving video.

In the Iraqi diving video a man dives off a cliff into dust/earth/mud after which people clap and he receives a score for his dive.

if this video clip is analyzed the following can be determined:

1. Hang Time
2. Maximum Height
3. Height of Cliff
4. Vertical Takeoff Speed
5. Vertical Impact Speed

(Assume air resistance is negligible in all of the following circumstances)

1. Hang Time

• Play the video clip in QuickTime. Count the frames in the man's diving trajectory. Distinguish between the diver's rising and falling portions.
  • total trajectory = 55 frames
  • rising = 7 frames
  • falling = 48 frames
• Using QuickTime. go to "window", then click "show movie info". In the window were it says "movie fps" are the number of frames per second.
  • 24 frames per second.
• Now calculate the amount of time using

time = (number of frames)/(frames per second)
t(rising) = (7)/(24) = 0.29 seconds
t(falling) = (48)/(24) = 2.00 seconds
t(total trajectory) = (55)/(24) = (hang time) = 2.29seconds

2. Maximum Height

• Use the amount of time of the diver falling to find the max height of the trajectory.

s = y_o+ v_ot + (at²)/2
y_max = 0 + 0 + (9.81 m/s²)(2 seconds)² / 2
y_max = 19.62 meters

3. Height of Cliff

• Find the vertical distance the diver jumps

s = x_o + v_ot + at²/2
s(vertical distance jumped) = 0 + 0 + (9.81 m/s²)(0.29)² / 2
s(vertical distance jumped) = .19.62 meters

• Subtract distance jumped from distance falling

(height of cliff) = (distance jumped)–(distance falling)
(height of cliff) = 19.62–.42 = 19.20 meters

4. Vertical Takeoff Speed

• Use the distance jumped in the equation

v_f² = v_o² + 2as
v_f = (v_o² + 2as)^0.5
v^_f = (0² + 2 *9.82 *0.42)^.5 = 2.87 meters/second

5. Vertical Impact Speed

• Use the distance falling in the equation

v_f² = v_o² + 2as
v_f = (v_o² + 2as)^0.5
v_f = (0² + 2*9.82*19.62)^0.5 = 19.62 m/s

Alexis Grisales -- 2004

Physics on Film pages in The Physics Factbook™ for 2005

• Feature Films
  • Tension in Spider-Man's webs
  • Speed of a car: Bad Boys II
  • Speed of a car: The Blues Brothers
  • Speed of a car: The French Connection
  • Speed of a car: Le Mans (Steve McQueen 1971)
• One Reelers
  • Speed of a car: C'était un Rendezvous
  • Speed of a car: The Run
• Short Video Clips
  • Speed of a baseball: Bird Baseball
  • Speed of a cliff diver: Iraqi Olympic Diving
  • Speed of a motorcycle: Loading a Bike
  • Speed of a snowmobile: Snow Jump

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