About scientific method?

Question

Why is it important to keep everything in experiment same except the item I'm testing?
Why can't I change hypothesis in middle of experiment?

Also I want to know about what is law of conservation of energy and law of conservation of matter,

Answer 1

well the item you are testing is your topic. The hypothesis is what you are testing about. These are necessary because without it you are doing no experiment.

Conservation of energy states that the total amount of energy (often expressed as the sum of kinetic energy and potential energy) in an isolated system remains constant. In other words, energy can be converted from one form to another, but it cannot be created or destroyed. In modern physics, all forms of energy exhibit mass and all mass is a form of energy.
When a piece of copper metal is heated in air, it comes together with oxygen in the air. Then if it is weighed, it is found to have a greater mass that the original piece of metal. If however the mass of the oxygen of the air that combines with the metal is taken into consideration, it can be shown that the mass of the product is within the limits of accuracy of any weighing instrument, equal to the sum of the masses of the copper and oxygen that combine. This behavior of matter is in accord with what is called the Law of Conservation of Matter: During an ordinary chemical change, there is no detectable increase or decrease in the quantity of matter.
Conversion of one type of matter into another are always accompanied by the conversion of one form of energy into another. Usually heat is leveled or absorbed, but sometimes the conversion involves light or electrical energy instead of, or in addition to heat. Many transformations of energy, of course, do not involve chemical changes. Electrical energy can be changed into either mechanical, light, heat or potential energy without chemical changes. Mechanical energy is converted into electrical energy in a generator. Potential and kinetic energy can be converted into one another. Many other conversions are possible, but all of the energy involved in any change always appears in some form after the change is completed.

Answer 2

This is a pretty good question. And the answer is, in one sense, scientists do this.

So, you start an experiment with a hypothesis - that is, an idea which you are trying to determine either true or false. But as you are doing the experiment it becomes obvious that it is really true.... OK, why continue on... but there might be something else interesting that has shown up, so you continue the experiment to be sure that you find out about that interesting new idea.

OK, is that changing the hypothesis, or did you really just finish the first experiemnt early and start a new one!

In real science this might happen like this..

Suppose you had a new medicine and you thought it would cure lung cancer. OK. you get a bunch of guys with lung cancer and you try to split them into two groups so the two groups are the same as much as possible. You figure you will give one group the new experimental medicine and the other group gets some standard medicine that you already tested before. You plan to keep all the patients on the medicine for three months....

But then, at the end of the first month half of the patients who get the new medicine died, and none of the patients with the old standard medicine? What are you going to do, keep on giving them the new medicine?

Or, what if it worked the other way.... after two months half the standard medicine guys died, and only 1/10th of the new experimental medicine guys died? Then what would you do.

It would be highly unethical to continue an experiment where you knew that some of the people you were working with were dying unnecessarily.

Answer 3

You need to have as few variables as possible that will influence the experiment.........whether or not your hypothesis is correct is irrelevant....so why change it?!