|
|
|
|
|||
power, as a general notion, expresses the ability of a physical body or system to perform a physical action or process (movement, heating, transformation,...). The word comes from ancient Greek: energeiai, meaning activity, work, indicating force, power, or vigor to act.
Mechanical energy, which is of two types:
kinetic energy: energy of moving bodies
potential energy: the energy of bodies in a force field
Chemical energy: it is stored in food, fuels, charged electric batteries and is released through chemical reactions.
Thermal energy: is the energy of the thermal agitation of the microparticles (atoms, molecules) that make up the substances, which can be transmitted in the form of heat, from a warm body to a cold body.
Electricity: is the energy of electric charges (electrons, protons, ions) and can be easily transmitted by the movement of these charges.
Electromagnetic energy: is the energy that is transmitted through electromagnetic waves (radiations).
Nuclear energy: is the energy stored in atomic nuclei, which can be released through nuclear reactions (fission, fusion).
In everyday life, energy is often associated with consumable substances (food, solid, liquid, gaseous fuels) or objects that ensure the operation of devices, which after being discharged must be replaced or recharged (electrical, disposable or rechargeable batteries).
During physical processes, energy exchanges occur between bodies/systems, as well as energy conversions from one form to another. Any transfer of energy is governed by a universal law of conservation of energy which states that energy is not lost, but merely transformed between different forms. In order for this law to be validated, energy must be measurable and the same unit of measurement can be used for all forms of energy.
Energy is a scalar physical quantity having in the international system the unit of measure: (Joule, from the English physicist James Joule).
Other common units of measurement:
1 cal=4.185J (calorie, old heat unit, then extended to measure energy)
1 kWh=3.6MJ (kiloWatt-hour, the energy consumed by a 1000W device for one hour)
Every day we use energy from various sources and it is interesting and useful to compare their prices relative to the same unit of energy measurement. Complete the table below, looking for (indicative) information and making appropriate calculations:
|
the energy source |
energy content |
COST |
unit cost of energy |
|
1L petrol |
32MJ |
9 RON |
0.28RON/MJ |
|
1L diesel |
|
|
|
|
1L LPG |
25 MJ |
4.5 RON |
|
|
1 m3 methane gas |
10.5kWh=37.8MJ |
3 RON |
|
|
1 ton of coal (coke briquettes+lignite) |
4500kcal/kg·1000kg=18.8GJ |
900 RON |
|
|
1 bag of wood pellets 15kg |
18MJ/kg·15kg=270MJ |
30 RON |
|
|
1kWh electricity |
3.6MJ |
1.5 RON |
0.42 RON/MJ |
|
1 kg of bread |
10.7MJ |
12 RON |
1.12 RON/MJ |
|
100g of chocolate |
|
|
|
|
1L of oil |
|
|
|
|
200g of butter |
|
|
|
|
1 kg of sugar |
|
|
|
