Why does efficiency decrease with the more energy is added When converting from electrical to kinetic energy?

Question

This is because i have recently done a investigation with a remote control car and found the energy put in and energy transfered to kinetic is significantly less each time it is charged for a larger amount of time (this is not the fault of the battery) and the only theory i can come up with to explain it is for the longer it runs the more energy escapes to sound heat and friction. (the more ideas the better and the more detailed the better aswell)

Answer 1

yes

Answer 2

please rephrase your question. you are either asking when you charge the car for longer periods why each time the batt is charged you get less work out of the vehicle for letting it charge longer?  This would not be the case over all as work would increase with voltage x amperage but it would be if you were comparing work per ampere because a battery charge cycle is not linear and slows as it approaches it's maximum capacity.

If you think about losses when comparing cold use to hot for energy loss, it could be that when energy is used to create kinetic movement, resistance is created.  the more movement, the more loss to resistance which is also non-linear (thus why fuel economy goes down the faster you drive your car)

if this is not what you are comparing, please be more specific.

Answer 3

Perhaps the more you have charged it, the more potential energy (stored energy) is kept in the battery. Thus the more is "suddenly" burst out. Its like a balloon for example, the more air in it, the more pressure inside, the more power it will have, but, there is also a time factor. The more pressurized a balloon is, the quicker the air will escape. According to newtons 3rd law. For every action there is a direct and opposite reaction. So the faster it will fly, but, this speed wont last long and die out quickly . Explaining the absurd result.

Answer 4

One reason is equation for heat generated due to current or power dissipated.  It is

power = current^2 * resistance

In your case the resistance is constant so as the current goes up the power dissipated (heat) will go up exponentially.

You will also have to know more about your motor.  The mechanical efficiency will be different at different rpms.  This is due to magnetic losses in the motor.

You mentioned heat and typically as things heat up they add resistance to a system both electrically and mechanically.  

Ambient temperature has effect on batteries also.  That is why automotive batteries sometimes are rated in cold cranking amps and warm cranking amps.  If your battery gets while charging unplug it immediately.  If it is cold maybe stuck in the fridge it will not charge as well either.