Introduction

1. Physics is science

Physics is the science that we use to understand how things work in our real physical world.
If we need, for example, to know where to place a satellite to orbit the earth in order to send us a photograph of the Arizona state every two hours, Physics gives the answer.
Physics has tools to describe a phenomenon. These tools are concepts, assumptions, equations and models. We use them to state a principle in Physics.
The concepts of mass, length, velocity and time can be used for the above example to state the principle that the distance where to place a satellite do not depend on its mass at all.

2. The areas within Physics

Like many subjects in Science, Physics is divided into areas. Generally, in Physics we find the following areas:

1. Mechanics: Motion and its causes
2. Thermodynamics: Heat and temperature
3. Vibrations and waves: High frequencies
4. Optics: light
5. Electromagnetism: Electricity, Magnetism and waves
6. Relativity: High speed of particles, light
7. Quantum Mechanics: Atomic and subatomic energy

3. The scientific methods

Generally, Physics follows the same procedure to set a law. the related main steps are:

1. Make an observation
2. Collect data
3. Formulate hypotheses
4. Make experiments
5. Interpret the related results
6. State conclusions to set a final formula.

The study of a phenomenon is generally complex because it involve many parameters to take account in order to give a good results. We use an approach that simplify the study. We use in this case a model to interpret the essential features and to disregard the less important parts. The important part to study is called the system.
If we want to use a radar to detect the speed of a car, we will be interested only in the speed of the car and the measurement given by the radar. Then the car and the radar constitute our system. We can reduce this system to obtain the short one composed by the velocity of the car and the measurement obtained from the radar. We are not interested in any other parameters such as the color of the car, the temperature around us, the sound of the car.

4. Hypotheses and models

Hypotheses are made from an observation. They are experimented in order to set a result of the form of a law.
Galileo, in 1638, made certain hypotheses (thoughts) that all of the objects fall with the same velocity from a given height; no matter how much they weight. He made then experiments in order to test these hypotheses and therefore stated a Physic's law that is The free fall law.
In this analysis, the air resistance is neglected. So we say that we have done an approximation.