After having thoroughly researched a topic, you should have some idea of what you think will happen in your experiment. This 'educated guess' concerning the outcome is called your hypothesis.
Your hypothesis needs to be worded so that it can be tested in your experiment.
To do this you need to express the hypothesis by saying what you think will happen when you change your independent variable. You need to say what you think will happen to your dependent variable (the variable that changes in response and depends on changes in the independent variable).
Not only must you do this - you also must word your hypothesis a way that you can easily measure and therefore test.
For example: "My hypothesis is that the cross sectional area of a hose pipe (independent variable) is proportional to the volume of water (dependent variable) that will be delieverd in a fixed time (control variable)"
Not every question can be answered by the scientific method. The hypothesis is the key. If you can state your question as a testable hypothesis, then you can use the scientific method to obtain an answer.
It doesn't matter if you end up dis-proving your hypothesis when you carry out the experiment - you are still adding to the wealth of scientific knowledge.
If you do an experiment that indicates your hypothesis was right then you still cannot say it was 'correct' - you then have to consider under what conditions your experiment proved that it was correct - then use a different range of variables etc.
The most influential approach to the scientific method is that of Karl Popper (1902 - 1994) who wrote about his ideas on the scientific method between 1938 and 1963.
Popper's idea about doing science is that you formulate a hypothesis, try to prove it wrong, and, from your results, formulate a new hypothesis.
Why not try to prove it right? Because you can't; you never know if there isn't one more experiment that will prove it wrong.... and scientific history shows us that this is the case.
Our current accepetd theories are only that - current - accepted (by the scientific community after exhaustive tests) theories (ideas people have had that make sense of what we know to dat - but are far from 'absolute truth'!)