CONSERVATION OF ENERGY
According to the law of energy conservation, energy cannot be created or destroyed.
It can only be transformed from one form to another or transferred from one place to another.
Much like matter is preserved during a chemical reaction and respects the law of the conservation of matter, energy also respects the famous phrase of Lavoisier:
“ Nothing is lost, nothing is created,
everything is transformed! "
Thus, according to this law, transformations and transfers of energy take place without the loss of energy.
For this law to be respected, however, it is important to be in the presence of an isolated system.
An isolated system is a system that does not exchange any matter or energy with its environment.
Such a system ensures that the totality of the initial energies is equal to the totality of the final energies obtained.
A thermos is an example of an isolated system, because this container makes it possible to conserve the content (like a soup) and the energy (the heat of the soup) without exchanges taking place with the outside.
The law of conservation of energy makes it possible to study transformations and transfers of energy.
For example, it can explain why a loss of potential energy in a system is compensated by an increase in kinetic energy, thus making it possible to conserve total mechanical energy (which is the sum of potential energy and kinetic energy).
For example, it can explain why a loss of potential energy in a system is compensated by an increase in kinetic energy, thus making it possible to conserve total mechanical energy (which is the sum of potential energy and kinetic energy).
》 EXAMPLE
A cart moves on a rail. Assuming that there is no friction, it is possible to determine the different types of energy present in different places.
At point A, the carriage moves and therefore has a certain amount of kinetic energy.
In addition, it is located at a higher point than the ground, which means that it has a certain amount of potential energy.
E k = 100 J ,
E p = 100 J ,
E m = 100 J + 100 J = 200 J
At point B, the speed of the carriage increased as the height from the ground decreased.
Kinetic energy has therefore increased, because potential energy has decreased.
E k = 200 J ,
E p = 0 J ,
E m = 200 J + 0 J = 200 J
At point C, the carriage slowed down as its height above the ground increased.
Kinetic energy has therefore decreased, because this energy is transformed into potential energy.
E k = 10 J ,
E p = 190 J ,
E m = 10 J + 190 J = 200 J
At point D, the carriage returns to the same point as it was at the start.
It therefore has the same amounts of energy as they had at the start.
E k = 100 J ,
E p = 100 J ,
E m = 100 J + 100 J = 200 J
The energy is conserved because the amount of energy at the start is the same throughout the movement of the carriage.
E k = 100 J ,
E p = 100 J ,
E m = 100 J + 100 J = 200 J
At point B, the speed of the carriage increased as the height from the ground decreased.
Kinetic energy has therefore increased, because potential energy has decreased.
E k = 200 J ,
E p = 0 J ,
E m = 200 J + 0 J = 200 J
At point C, the carriage slowed down as its height above the ground increased.
Kinetic energy has therefore decreased, because this energy is transformed into potential energy.
E k = 10 J ,
E p = 190 J ,
E m = 10 J + 190 J = 200 J
At point D, the carriage returns to the same point as it was at the start.
It therefore has the same amounts of energy as they had at the start.
E k = 100 J ,
E p = 100 J ,
E m = 100 J + 100 J = 200 J
The energy is conserved because the amount of energy at the start is the same throughout the movement of the carriage.
Hi pavan
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