<em>Answer</em>
<em></em>
<em>Clastic sedimentary rocks are made up of pieces of pre-existing rocks. Pieces of rock are loosened by weathering, then transported to some basin or depression where sediment is trapped. If the sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock</em>
<em></em>
<em>Hope this help's you</em>
If both of them were travelling anti parallel to each other. (parallel but in opposite directions)
Answer:
I feel it's to easily differentiate the positive from the negative...... like in gram staining of bacteria, the colour tell us which bacteria is gram positive or gram negative...... I just feel that this is science and it is advisable to know what the opposite result of an experiment should look like.