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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You’re not doing work, because the force is not in the direction of motion, it’s perpendicular to the direction of motion. Sort of like how you don’t have to spend energy fighting gravity just to coast on level ground. When you turn, the steering forces are pointing sideways, not backwards.
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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