## Tuesday, December 9, 2014

### Newton's Laws and the Hybrid Car

I think the biggest reason I purchased a hybrid car was my fascination with the engineering that gives the car such good efficiency. Understanding the basic physics of the car possibly might increase the mpg that your car obtains, this past summer I had reached a 53.5 mpg average. The following post is my attempt to relate some basic physics to how the hybrid car functions. If there are great inaccuracies let me know.

Newton's First Law – object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.   Law of Inertia

This means that a car that is not moving will take a force to get it moving, this normally is provided by converting chemical energy into mechanical energy by the burning of gasoline in an internal combustion engine. Explosions in the cylinders  of the engine rotate a crankshaft that connects to gears and shafts resulting the in drive wheels of the car rotating which moves the car.

Second Law – states that force is proportional to acceleration but acceleration is inversely proportional to mass. The formula Force = Mass x Acceleration relates to this law and the unit of force is the Newton.

Newton’s Second Law relates to how much force is needed to move the car for the mass of the car.  Greater force is needed to accelerate faster and with a larger mass.

Normally a hybrid car is powered by both a internal combustion engine burning gasoline and an electric motor powered by rechargeable batteries.  Batteries are recharged by the internal combustion engine but also through capturing “kinetic energy” of the moving car, this is known as “regenerative braking”.

In the hybrid car when it is coasting or braking, the internal combustion engine is turned off and the kinetic energy is converted to electrical energy and stored in batteries. This can be seen in the Energy Monitor display in a Prius hybrid car, the dashed line with the arrow points from the front wheels to the battery.

Accelerating from a Stop in a Hybrid Car

Thinking of Newton’s First Law again when accelerating the hybrid car, when you gently press on the accelerator pedal the car will start moving with the electric motor. Some of the electricity supplied from the battery may have come from what was generated in the coast and the process of stopping before the car came to rest.

In the Energy Monitor diagram above the arrow points from the battery through the electric motor and towards the front wheels.

Once the car is moving less force is needed to keep it moving. Based on many factors the internal combustion engine will start to help power the car at some point. If the accelerator pedal is depressed hard from the start, the internal combustion engine starts right away along with the electric.

In this diagram the brown arrows indicate the internal combustion engine is helping to power the car and charge the battery.

Bill Kuhl