Today, it is not uncommon for parents to call their children because they need help performing a simple task on a computer, like ripping a CD and using an email program to mail a song to someone. Typically, parents teach children, not the other way around. What creates situations in which parents have to turn to their children for help

The rate at which the meaning of words change

Explanation: certain slang use or text phrases may be hard for a parent to understand especially considering how fast words are given different meanings. An example can be the word "cap" which before was just something you wore on your head, to also being a slang word for lying.

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

what words? are you talking about to complet what sentence