Physics is the study of nature and the laws that help us in understanding all natural phenomena. This is because everything consists of matter and energy and interacts in space and time. Principles of physics are key elements in many scientific disciplines. In chemistry, they are applied to study the interactions of atoms and molecules. In many engineering branches, we use the laws of physics in designing new technologies and devices. Physics also describes the chemical processes that take place in the human body, making possible the development of techniques and devices used in biological and medical sciences. The laws of physics are used by all the disciplines, and the study of physics greatly contributes to our understanding of other sciences. Many physical quantities that are defined by the laws of physics can be expressed as a combination of length, mass, and time quantities. Length is a physical measurement of distance that is measured in the SI unit of the meter, mass with the unit of the kilogram, and time with the unit seconds.