Tutorial details

Section I of the tutorial helps students develop a procedure they can use for finding displacements of objects in any reference frame. The physical context is identical to that of the pretest: two spaceships move relative to one another while a shuttle travels from one spaceship to the other. They draw diagrams that show the initial and final positions of both spaceships and the shuttle in the reference frame of each of the spaceships. On the basis of these diagrams they compare the initial and final distances between the ships and the displacement of the shuttle in the reference frame of each ship. Students are also led to recognize that all objects moving with the same velocity measure the same displacement for all objects and thus can be regarded as being in the same reference frame.

In section II of the tutorial, students consider two objects (a truck and a car) that move in the same direction relative to a long, straight road. The truck has uniform velocity and the car is slowing down relative to the road. The truck passes the car during the interval considered. Students consider the motion of the car in the reference frame of the truck. They are led to recognize that the direction of motion of an object and whether the object is speeding up or slowing down can depend on the reference frame in which the motion is measured. A specific error that is addressed explicitly is the tendency of students to confuse relative position and relative velocity in the context of objects that pass one another.

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Before working through this tutorial, students should have previously studied position, displacement, velocity, and acceleration in the laboratory frame of reference. The term frame of reference should have also have been introduced.

Equipment

List

• handouts
• white board or large sheet of paper with markers

Discussion