What do you mean by “perfectly converted”? There is no such real thing as conversion to only one other type of energy, so there’s no way to visualize that. Energy is converted all the time, just not 100% of it. In your car kinetic energy example, it’s converted to sound through screeching tires, through whooshing air, through vibrating engines, and it’s converted to heat through friction between the car and air, and the friction between the tires and the road. There isn’t really any light being created.
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