Ski Luge

What is gravity and how does it affect objects in the universe?

Background:

Introduction: Anticipation of the luge competition at the Winter Olympics brings visions of high speed, sharply banked curves, a trough like track, and tests of skill in maneuvering the tiny sled. The Winter Olympics scheduled for Utah's mountains in 2002 promises to present an event as exciting as the first Olympic luge competition held in Innsbruch, Austria in l964. The approximate 1335 meter-long track at Utah Winter Sports Park starts at an altitude of 2233 meters and descends to a base altitude of 2142 meters. The luge and rider, after an initial pull off aided by start handles, begin the descent of the track. The timing for the race starts at the instant the sled and rider reach the end of the horizontal start area and commence to move downward. Then several forces acting on the sled and rider begin to play major roles on the movement down the track.

Science: Gravity is the force which pulls the luge and rider faster and faster downward. Also acting on the luge is friction of the ice surface on the sled and the drag caused by the air friction on the rider and sled. Other factors which play roles are the slope of the track, the conditions of the ice surface, types and numbers of curves and the initial start velocity as the luge begins the descent. In this lesson, all frictional forces have been reduced to zero, curves have been eliminated from the course, and so the acceleration of the luge and rider are affected only by the slope of the track. With no frictional forces on the track surface, the acceleration is equal to g x sinθ where θ is the slope angle and g is the acceleration due to gravity on the particular cosmic body. Remember, as θ approaches 90 degrees (vertical), the acceleration approaches 9.8 m/s2 which is the acceleration due to gravity for a free-falling body on Earth. In the case of the luge course depicted in this lesson, θ is approximately 4.5 degrees and the corresponding acceleration is about 0.76 m/s2 on Earth. Likewise, after the 55 seconds for the luge and rider to reach the finish line, the final speed is approximately 42 m/s ( ie. 0.76m/s2 x 55 s) on Earth.

Preliminary Knowledge: Prior to working on these lessons, students will be expected to know the relationship between speed, distance and time and should be capable of using the formula, average speed = distance/time. The term "speed" will be used in the On-Line Student labs, however, teachers may want to review the difference between "speed" and "velocity".

Invitation To Learn

  1. What is a Luge?
  2. Questions to Consider:
    1. What force or forces cause the luge and rider to move down the track and gain speed?
    2. If gravity is mentioned, explore student ideas about this force, i.e. Is gravity always present?
    3. Is there any way to escape its effects?
    4. Can it be changed in intensity?
    5. What happens to the luge run if it were held on the moon?
  3. Variables need to be measured so average speed can be calculated for the run.
    1. formula: average speed = distance/time.
    2. Practice Problems
    3. Speculate on how you might actually measure distance and time for the luge moving down a mountain side.
  4. Give examples and explain what other forces may be acting on the luge and rider and how these forces affect the speed.

Lab Procedure

Pre-Assessment:

An optional group of questions to test your students' present knowledge of the effect of gravity on moving objects.

  1. If a skier slides down a steep slope, what will happen to the speed of the skier as he/she proceeds further down the slope?
  2. What force or forces act on the skier while on the slope?
  3. If the skier could try the same slope on an extra-terrestrial body the size of our moon, what effect would less gravity have on the average speed of the skier? What if the body where larger than our Earth, what effect on average speed would you predict?
  4. Gravity is a force produced by all bodies. If you could turn the force of gravity off, what would happen to a skier on the same steep slope?

Complete Speed of Falling Objects Lab