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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Firstly, as was mentioned, there’s no physics-work done if the acceleration is perpendicular to the movement, which is what happens when you go in a circle.
Secondly, the energy doesn’t go anywhere in an idealized setup, because energy isn’t a vector quantity. A car going the same speed in the opposite direction still has the same kinetic energy.
If you’re looking for where the momentum went, there’s a force exerted on the road by the tires to keep the car going in a circle. The force on the car is toward the center of the circle, like the orbit of a moon or when you swing a mass on a string. So the road and the planet it’s attached to will have their momentum changed very slightly in the opposite direction.
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