## Program 17: SR Experiment with 4 trains

### Introduction and Purpose

The purpose of the program SR.BAS is to answer the question if the length of two rods in any reference system is the same when the two rods move in opposite directions and their speed is the same. Accordingly to Special Relativity the answer on that Question is Yes.

To get a copy select: SR.BAS
To see the listing of the program select: SR.HTM

### Program Operation

The program consists of three demonstrations and each demonstration consists of 6 steps.
• Demonstration 1 shows the position of 4 trains at 6 moments or steps
• Step 0 is the initial state. At this moment all the 4 trains are at rest.
Train 1 stays at rest and the three other trains start to move to the right with speed v.
• Step 1 shows that the trains 2,3 and 4 move to the right.
• Step 2 is identical as step 1. At this moment the situation for the trains 3 and 4 changes.
• Step 3 shows the same situation for train 2 but not for train 3 and 4.
In the track frame of train 1, train 3 moves to the right with twice the speed and train 4 has stopped.
In the track frame of train 1, train 3 has a speed v to the right relative of train 2 and train 4 has a speed v to the left realtive of train 2.
• Step 4 and 5 is identical as step 3 but later.
• Demonstration 2 is almost identical as demonstration 1 except that there are 2 more trains.
• Demonstration 3 is almost identical as demonstration 1 except that the initial position of the trains different is. Train #3 starts from the left and train #4 starts from the right.
• In step 0 the trains starts to move to the right.
• In step 2 the situation for the trains #3 and #4 changes. Train 3 increases (doubles) its speed and train 4 stops.
• Step 4 shows that the two trains are at the same situation. However their lengths are not the same in the track frame of train 1.

In order to see the three demonstrations hit ENTER.

### Program Description

L0 is the length of the train in the rest frame. L0 is 300000 km.
L1 is the length of the train with v to the right.
L2 is the length of the train with 2*v to the right.
dt is the time between each step in seconds. dt = 3
v is the speed to the right. v = 300000/dt = 100000. km/sec

### Reflection

1. What the demonstration clearly shows that in the track frame of train 1 the speed of the two trains 3 and 4 is different. What is more important that the length is different.
2. What the demonstration IMO shows that in the track frame of train 2 the speed of train 3 and train 4 is the same (absolute). It also shows that the length of both trains are different. What is more important the length of train 4 is longer as the length of train 2.

### Feedback

None

Created:26 January 2001