What is the dangers of Global Variables in Drupal specifically?

What is are the dependant variables, independant variables, and controlled variables in a science experiment?

• In a science assignment I need to construct the "perfect" helicopter by testing different variables such as wing length, width etc. i am not sure what the difference between the three types of variables are. also when testing wing length i would for xample test 2cm 5 times, then 3cm, then 4cm etc, but what wing width would i use? and same for after that when i would be testing the perfect wing width, what wing length would i use?

• Answer:

  well this experiment seems to be a trial and error one. you might have to try out all your possibilities (yeah can be a bit tedeous) and then find the values which are the most stable. hope it helps to answer your question