Something I don’t quite understand from a physics standpoint. Imagine a car going down a road approaching a roundabout, on neutral; it can follow the roundabout 180 degrees and start going in the reverse direction while only losing a little speed/energy. But the car did a lot of “work” in the physics sense — a multi-thousand-pound vehicle completely reversed direction in a few seconds. How is that energy redistributed (force diagram, etc) to show where the energy for all that work came from?
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Tires against the ground.
A tire is going to resist motion not in line with the rotation. Turning the axis of rotation of the wheel/tire means forward motion of the car results in a side loading of that wheel, which tends to turn the car, adjusting its velocity. Frictional losses are happening throughout the whole process: air resistance, squishing the tires (and getting only a little back from un-squishing them. Modern cars are engineered to be efficient and have smaller losses against friction, but overall there is a lot to account for and ignore.
A simpler way is a mass on a string, or a ball rolling through a curved track. The string exerts a force on the mass, or the track exerts a force on the ball.
For any mass of car, the mass of the earth is going to be way bigger. (citation needed)
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