FRAMES OF REFERENCE

Film Loop: Galilean Relativity III: Projectile fired vertically.

Length: 3:00 min., Black and White, No sound

A rocket tube is mounted on gymbal bearings making it free to turn in any direction. When the gun is hauled along the snow-covered surface of a frozen lake by a "ski-doo", the gymbals allow the tube to remain verticaly pointing upward in spite of some roughness of path. Equally--spaced lamps along the path allow one to judge whether the ski-doo has constant velocity or whether it is accelerating. A preliminary run shows the entire scene; the setting is in the Laurentian mountains in Quebec at dusk.

Four scenes are photographed. In each case the flare is fired vertically upward. With care you can determine the paths experimentally. Scene 1: The ski-doo is stationary relative to the earth. How does the flare move? Scene 2: The ski-doo moves at uniform velocity relative to the earth. Describe the motion of the flare relative to the earth; describe the motion of the flare relative to the ski-doo. Scenes 3 and 4: The ski-doo's speed changes after the shot is fired. In each case describe the motion of the ski-doo and describe the flare's motion relative to the earth and relative to the ski-doo. In which cases are motions a parabola?

How do the events shown in this film illustrate the principle of Galilean relativity? In which of the frames of reference shown here does the rocket behave the way you would expect it to behave, knowing that the force is constant, and assuming Newton's laws of motion?In which systems do Newton's laws fail to predict the correct motion?