Additional Info

• ID Code: P1-02
• Purpose: Illustrates an inertial frame of reference
• Description:
  A metal frame is suspended such that it can be held up by an electromagnet, and then drop freely onto a cushioned shock absorber. A pair of spring-powered cannon firing one-inch ball bearings are directly in line with holes in two plexiglass plates, one in the center and one on the side opposite the cannons. The second plate has sacks on the holes to collect the projectiles if they pass through the holes. Beneath the frame is a net to catch projectiles that do not go through the holes.

  Engagement Suggestion:

  • Before carrying out the experiment, encourage students to predict what will happen to the projectiles.
  • Will the level and angled cannon behave differently?
  • Once the students have seen it in action when at rest, have them make predictions again about what it will do in free fall.
  

  Background:

  If the frame is at rest, the projected balls fail to even go through the first set of holes because they are deflected by gravity. As they travel, they are pulled downwards, following parabolic paths with respect to the frame. If the frame is raised, held in place by an electromagnet and released, it falls with the acceleration of gravity and becomes a "local inertial frame of reference." The balls are automatically fired by a gravity switch when the frame begins to fall. The balls will travel along straight lines in the local inertial frame of reference and end up in the sacks before the frame stops on the shock absorber.

• Availability: Available
• References: REFERENCES: (PIRA unknown.)
• Loc codes: FS0
• Videos-1: Slow-motion video
• Videos-2: In falling reference frame