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A physicist analyzing a car making a tight turn says there is no real force pushing the passenger sideways relative to the ground. What is the physicist using as the frame of reference?
AThe passenger's own body as the frame
BThe turning car itself as the frame
CThe car's steering wheel as the frame
DEarth, nearly an inertial frame here
Answer & Solution
Correct answer: D. Earth, nearly an inertial frame here
1. An inertial frame of reference is one in which all forces present have an identifiable physical origin.
2. The physicist chooses Earth as the frame because it is very nearly an inertial frame of reference.
3. In that frame, the passenger simply travels in a straight line by Newton's first law while the car turns beneath them, so no real sideways force on the passenger is needed.
4. The car itself is a non-inertial frame because it is accelerating, which is exactly why using it as the frame produces the fictitious sideways push instead of the correct picture.
_Source: OpenStax College Physics (CC BY 4.0), Ch 6 "Uniform Circular Motion and Gravitation", section 6.4 Fictitious Forces and Non-inertial Frames: The Coriolis Force_
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