Relative motion

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1. Relative Motion–Frame of Reference

It’s All Relative
Student Instruction Sheet

You are going to face several challenges with respect to your motion and various frames of reference. In each of the following challenges, a different variable will be changed or modified.

Equipment and Materials
• Computer with USB Port • PASPORT USB interface • PASPORTMotion Sensor • DataStudio software • 1.2 m PAScar Dynamics System • Cart Adapter Accessory • PAScar (2) • Cardstock • Masking tape

• Student Instruction Sheet • Student Response Sheet

Safety Precautions
Remember, follow the directions for using the equipment.

What is your velocity right now? Perhaps surprisingly, the answer is “it depends.” Are you being asked to describe yourspeed within the classroom? Your speed on a spinning Earth? Your speed in a moving solar system traveling within a rotating galaxy? As you can see, the question of your velocity depends on the environment in which the motion occurs. In physics, this is referred to as “the frame of reference.” For example, if you are sitting still in your classroom, the classroom is your frame of reference andyour velocity is zero with respect to its walls since


Student Instruction Sheet 35

1. Relative Motion–Frame of Reference


you are neither approaching nor receding from them. But what if you were to get up and walk around, or if the walls were to move? What is your velocity now within this frame of reference?

Before beginning the eLab, complete theprediction portion of the Student Response Sheet.

Computer Setup
1. Plug the USB interface into the computer’s USB port. 2. Plug the Motion Sensor into the USB interface. This will automatically launch the PASPortal window.

3. Choose the appropriate DataStudio configuration file entitled

01 Relative Motion CF.ds
Note: Configuration files automatically launch the appropriatedisplay(s), sampling rate(s), etc.

Equipment Setup
1. Set up and level a dynamics track with an end stop at one end of the track.There are two ways to insure that the track is level. The first method is to use a bubble level. The second method is to place the track on a horizontal surface. Level the track by placing the PAScar on the track. If the cart rolls one ways or the other, use theleveling screw at one end of the track to raise or lower that end until the track is level and the cart does not roll one way or the other. 2. Connect a PASPORT Motion Sensor to a PAScar using the Cart Adapter Accessory. Set the ‘range select switch’ on the top of the Motion Sensor to the Cart icon (short range). 3. The cart with the Motion Sensor represents you and will be referred to as PAScar #1.36

Student Instruction Sheet



1. Relative Motion–Frame of Reference

4. Place the card stock onto the second car by pushing the card into the slots on top of the PAScar. This car will be referred to as PAScar #2.

card stock PAScar #2

Motion Sensor

End Stop level dynamic track


PAScar #1 (YOU!)

Note: Insure that the gold disc is pointingdirectly at the card stock target. 5. Place PAScar #2, with the card stock, at the end stop on the track. 6. Place PAScar #1, with the Motion Sensor attached, at the other end of the track. 7. Set the plunger on PAScar #2 at the first, i.e. lowest, setting and place the plunger against the end stop. Try a few practice launches to make sure that you can release the cart smoothly.
Note: For all theinvestigations in this lab, position the cord from the sensor so that the cart can move freely. It may be necessary for you or a lab partner to hold up the cord so that it doesn’t drag on the track or the lab bench.

Record Data Challenge #1
1. To collect data, click the Start ( the plunger. 2. Just before the two carts collide press the Stop ( ) button. ) button and then quickly release...