# Energy

The word energy is used very often today. It is used by scientists, engineers, artists, doctors, teachers, even mystics, always referring to something that makes things happen or exist.

At this point in our course, we will begin to understand what energy is. Think of a very common day in your life. In everything you do or use, energy is present. The foods you consume provide you with energy for your vital functions. The shower you shower with warms the water, converting electricity or combustion of a gas into heat.

We turn on the light to read a book, turn on the TV to watch a program, etc.

Everything we do involves energy.

In physics we classify energy into: movement energy (mechanical), sound energy, light energy, electric energy, thermal energy, among others.

At this point, we will define energy from the mechanical point of view, which is the energy of motion.

• Mechanical energy is the ability to displace a body, ie to perform work.

The unit of energy, therefore, is the same as Work. In the International system, this unit is the Joule (J).

Energy is neither created nor destroyed. It transforms from one form to another. This fact characterizes the energy conservation law, one of the most important laws of nature.

For example, the chemical energy of gasoline, as a result of the combustion that occurs in car engine cylinders, is transformed into mechanical energy, which allows the car to travel. But this transformation is not complete, because part of this energy is transformed into heat, which is also a form of energy, as we will see later. Therefore, we say that part of the energy is lost (dissipated as heat).

## Potential energy

Whenever an object is located at a certain height from the ground, and we simply drop it, it goes into motion. Where do you get the energy to get moving?

In reality, it does not obtain energy at this moment, but it already has an amount of movement energy, ie mechanical energy, stored. This energy that the body already has potentially is called gravitational potential energy.

The potential gravitational energy is greater the higher the body weight and the higher the height the body is in relation to a given frame.

In mathematical language we have:

on what: m it is the mass of the body;

g is the acceleration of local gravity;

H is the height of the body relative to the reference level.