# Discovery Science: Physics – Energy and Matter

## Earth Science: Physics and Technology – Physics  – Energy

Even in ancient times or earlier, humans have been wondering about the matter of the world. The idea of four basic elements was widespread until the Middle Ages.

These elements were fire, water, earth, and air. Modern physics poses the same question about nature and its subject matter in many different new ways.

### Physics – Energy and Matter

Every natural process is an exchange or conversion of energy. Mass and energy are equivalent due to the fact that mass is a characteristic of matter and a form of energy.

Generations of physicists have been studying the connection between force, energy, and motion for centuries. Finally, in the 19th century, a concept was formulated to answer this equation, a term derived from the Greek word ergon. The idea originated from the question of how machines accomplish mechanical work (moving a body through force).

Scientists today define energy as the ability of a machine, a living organism, or any other “system” to do work. A car, for example, filled with fuel as energy can transport persons
and goods; the gravitational energy of the Earth causes water to flow toward the ocean, as well as apples to fall off trees and skiers to speed down a trail with hardly any effort at all.

There are many different types of energy: kinetic energy, thermal energy, (bio-) chemical energy, radiant energy, atomic or nuclear energy, electric and magnetic energy, and gravitational energy.

All planets, rocks, molecules, and living organisms in the universe have one or another type of energy acting upon them, frequently even several at a time. All processes happening in the universe involve an exchange or a transfer of energy from one form into another.

Physical quantities

In physics, physical quantities are defined and often represent certain characteristics that can be given in measurable units. Energy, the most important quantity, has the unit “joule” (J; after James P. Joule, 1818-1889).

Mass is measured in pounds, time and space in seconds (s) and feet (ft), and speeds in feet per second (f/s). Force has the unit Newton (N; after Isaac Newton, 1643-1727). We calculate newtons with the formula 1 N = 1 kg x m/s2 and joules with 1 J = 1 N x m. Electrical units are voltage (volt, V), amperage (ampere, A), or resistance (Ohm, Q).

Albert Einstein, who won the 1921 Nobel Prize in physics, revolutionized this field when he was able to explain the association between mass and energy in a simple way with his concept of mass-energy equivalence formula (E = mc^2).

### CONSERVATION OF ENERGY

The concept of energy is part of the most important law in physics: the law of conservation of energy. This law states that the sum of all types of energy in the entire universe always remains the same.

The same is true for all so-called closed systems such as machines, animals, and atoms that do not exchange any energy or matter with their environment.