Final answer:
To determine if it's more energy-efficient to stop the engine or let it idle, it depends on the duration of idling. For short periods, starting the car may use more energy due to the initial fuel and battery load, but for longer idling times, turning off the engine may save fuel. The car experiences energy transformation and consumption as soon as the engine is running.
Step-by-step explanation:
Considering the scenario of whether stopping your car engine and starting it again uses less energy than letting your car idle for a specific duration, the answer can be nuanced.
For short idling periods, the energy required to start the car, which includes the initial fuel consumption to power the engine and the load on the battery, might be more than the fuel required to just let the car idle. However, for longer periods of idling, the cumulative fuel consumption from idling can exceed the energy required for starting the engine, making it more energy-efficient to turn off the engine and restart it.
A car is not a closed system; it requires constant energy input in the form of gasoline or electricity. When a car idles, it still burns fuel at a slower rate compared to when driving, but it's not at rest. If a car is never turned on, it uses no energy, but as soon as the engine runs, it starts consuming fuel, even if the car is not moving.
From a physics perspective, when you start the engine of your car with the transmission in neutral, there is a conservation of angular momentum which causes the car to rock in the opposite direction of the engine's rotation. This is a temporary effect and the angular momentum of the car is not conserved for much longer than a few seconds.
Furthermore, energy changes and transfers occur when a car accelerates and moves. For instance, a car climbing a hill converts chemical energy from fuel into gravitational potential energy, which is then typically lost as thermal energy to the environment or kinetic energy when the car descends.