This experiment again uses a detector based on two rows of scintillator tubes. The two rows are spaced 1 meter apart.

From the previous labs you learned that while the cosmic rays often are detected traveling straight down, they also arrive at a variety of angles. A cosmic ray traveling straight down travels one meter between detection times, but a cosmic ray traveling at an angle will travel farther between detection times. In order to know how fast a cosmic ray is going, you need to know two things:

1. The distance traveled.
2. The time it took to travel this distance.

Velocity is defined as displacement divided by the change in time. In our case, the displacement is the distance that the cosmic ray traveled between the tubes it hit. That means if the cosmic ray hit the tubes at an angle, you will need to use some trigonometry to find the distance that the cosmic ray traveled. (Don't worry, it's easy.) To help you find this distance, you can generate a protractor by clicking where you would like to center the protractor and dragging the mouse until the protractor is as big as you need.

With the cosmic ray's angle and the fact that the rows of tubes are 1 meter apart, you can determine the distance the cosmic ray traveled, this is the cosmic ray's displacement.

To help you determine the time the cosmic ray took to travel between the two rows of tubes, one timing scope has been attached to each row of tubes.

The top timer records the time at which the cosmic ray was detected by the top row of tubes. The bottom timer indicates when the same ray was detected at the bottom row of tubes. The actual time of travel between the two rows is the difference between these two times.