Motion Energy Explained

Understanding the way energy works in conventional hybrid and all-electric vehicles can help to deepen our appreciation for them and may even make them more desirable for ownership.

Put simply, the definition of energy is the capacity to do work. Referring to the First Law of Thermodynamics, we know that all energy of the universe is constant to which none can be added nor can any be taken away. The law further states that energy cannot be created or destroyed; it can only change from one form to another. Examples of this include heat changing into light or chemical energy turning into mechanical energy for motion. Of course, these changes don't happen on their own.

Energy is divided into two categories: potential and kinetic. Potential energy is unused energy or energy waiting to be used. On contrast, kinetic energy is the energy of full motion. You might recall learning these concepts while in grade school during physics or chemistry class. Let's review how energy can change form as it applies to vehicles.

Potential To Kinetic

When an object at rest is being put into motion, potential energy is converted into kinetic energy. A tank of gas in a parked car is in a state of potential energy. Once the fuel is ignited and combustion ensues, the vehicle accelerates or moves with increasing speed. That movement is the state of energy in motion - kinetic energy. When that vehicle comes to a halt employing the use of brakes motion or kinetic energy is transformed into heat energy. This is still kinetic energy of moving energy; it's just in a different form. The heat energy that is released from friction caused by the application of the car's brakes is lost. Hybrid cars have found a way around this wasted energy with the technology known as regenerative braking.

An all-electric car and even a hybrid in some extent when already in motion has used up the potential energy (in this case, potential "chemical" energy) stored in the battery and has converted that potential energy into electrical energy. Electrical energy is what drives the vehicle's motor, which is transformed, into kinetic energy (in this case, kinetic "mechanical" energy). This kinetic energy is what moves cars wheels forwards or backward.

When the vehicle stops, a part of the kinetic energy is changed to heat because of brake pad friction, which simply escapes upwards since heat rises. Nearly all of this energy is preserved before it can escape as electricity. This is done with the use of regenerative braking and is that energy is restored in the vehicle's battery as potential (chemical) energy. If it were not for the regenerative braking system, this heat energy that could be captured and re-used later would simply be lost upwards into the atmosphere. Regenerative braking creates the effect of getting free energy. What is really happening is that less energy is being wasted.

Flywheel power units being incorporated into hybrids may be a way to use energy more efficiently and do away with having to convert heat energy back into stored potential energy. Though this is still in the developmental stage, there is evidence that it is close to a reality. With flywheels installed, stopping your vehicle will not turn the energy into heat, which is difficult to harness and re-use. Instead, the kinetic energy is channeled into a spinning flywheel. The flywheel itself is driven by a motor and that motor is powered by a generator. The energy is stored in the flywheel and is therefore not wasted at all. This would accomplish effective energy conservation.

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