Let's stop here for a second. It is a dry, though very important thing as without energy nothing would work. Lots of energy exists. Heat, electricity, potential energy etc. What makes a difference for us is that each substance has an energy level. The transition between these energy levels – i.e. between its temperatures – goes along with energy transmission.

The point where the substance has no heat energy at all is the absolute zero temperature, i.e. 0 Kelvin degrees, or on the Celsius scales –273°C. At this extreme low temperature the particles of a substance are not in motion at all.

Luckily, our environment is warmer than this, as so the particles of a substance are in motion, according to its temperature.

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Let’s take an example. Rubbing two wooden sticks together, first they heat up, than they start burning. That’s the way fire has been created without matches, by our ancestors. 

What happened here? The particles in the wood start moving quicker, in effect of the energy input. The accelerated particles clash more often and as it happens more and more often, in effect of the released heat the particles reach their burning point. The wood starts burning.

What makes it interesting that this heat was transmitted by the energy. The same thing happens when we electricity for cooling. The energy input causes more pleasant temperature for us, but it does make a difference if it is let outside through the walls, through the badly closed locks or it is kept in the room. If we pay attention, the energy which has been input can be saved.


As we have seen, energy is emitted or absorbed by temperature. Radiant heat transmission is also possible both ways. Heat or cold can be radiated as well.



If we take off our gloves during winter-time, even if it is not windy, our hands get cold; the air, even if no draught is present, transmits the temperature of the cold substances around us, the ground, the ice, the snow and the air itself also has its own temperature and energy level.


A widely known heat transmitter device, including heating and cooling systems, which works only one way, is the fridge. The heat from the warm watermelon is transmitted to the black grid at the back of the fridge. Don’t even try to touch it, it is so warm.

Heating and cooling systems