The specific power is the Ratio of a power (out of W) by a Masse (in kg). The specific power is thus expressed in the international Système in W/kg ; it translates the capacity of a device of a mass given to generate a power.
Fields of application
The specific power is mainly used in the fields of transport and the mobile devices. Indeed the acceleration and the speed of a device depend at the same time on the mass and the power. The specific power is usually used to compare Véhicule S or Moteur S, as well in the field of the Automobile S, as in that of the motor bikes, the Train S, the Avion S or the armored vehicles. It is simply the power developed by (or them) the Moteur (S) divided by the Masse of the vehicle or the engine).For the Aviation and the Astronautics, it is often initially the specific power of the engine which is taken into account.
One can also define the specific power of other devices, systems and mechanisms. That makes it possible to give an indication of compared performances, and in particular when various technologies clash, and this in many fields, such as for example the electronic of power, the transformation energy, the food with cutting, etc
Numerical example
The power ratio/mass is often used like an indicator of the probable performances of Accélération.Let us take, for example two current motor vehicles designed for radically different uses. Let us compare their ratios: mass theoretical vehicle/power of the engine.
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For a Renault Twingo
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For a Bugatti Veyron 16.4
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Is a specific power (390/53,8) = 7,25 times higher, one from of deduced that Bugatti would be equipped with an acceleration seven times higher.
Density power density
Another ratio can be defined, the density power density, which are the power report/ratio provided by, the Volume occupied by the device Moteur and the accessories essential to its operation. This report/ratio can have in certain cases more importance than that of the specific power.
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