A mixture of substances can often be separated into the original substances by using one or more of these characteristic properties. In chemical reactions the total mass is conserved. Substances are often placed in categories or groups if they react in similar ways, for example metals. Chemical elements do not break down by normal laboratory reactions such as heating, electric current, or reaction with acids. There are more than 100 known elements which combine in a multitude of ways to produce compounds, which account for the living and non living substances that we encounter.
All matter has a definite structure which determines physical and chemical properties.
And Forces The motion of an object can be described by its position, direction of motion, and speed. This motion can be represented on a graph. An object that is not being subjected to a force will continue to move at a constant speed and in a straight line. If more than one force acts on an object, then the forces can reinforce or cancel one another, depending on their direction and magnitude. Magnetism is a form of energy because its forces can do work.