I was thinking, is there such a thing as negative $g$-force? What if a person is decelerating really quickly? Does that have the same effect as when a person accelerates really quickly? Are the $g$-forces similar?
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2 Answers
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They're identical - the only difference is the frame of reference you use.
Picture a car accelerating north at 10m/s/s. Intuitively, for the driver, this is a positive g force because we're used to accelerating forwards in a car, but if you ask what the acceleration to the south is you get minus10m/s/s. Ditto when the car decelerates, what the driver may view intuitively as deceleration is actually acceleration towards the south.
Obviously, when it comes to designing car seats and airbags, the frame of reference will match intuition, but this is just to make the maths nice and easy, you could set it up completely differently.
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$\begingroup$ I will add this fact. Note that impacts are of 1000g order, and you know their damage. So yes, your body is not prepared for abrupt changes in (de)acceleration. Why?. Your bones and skin is not ready for support those force loads. Both negative or positive. $\endgroup$ Commented Nov 26, 2017 at 4:01
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Hint: Note that acceleration wrt. one inertial frame is deceleration wrt. another inertial frame. So because of Galilean invariance in Newtonian mechanics, there cannot be any intrinsic physical difference between the notions of acceleration and deceleration.
answered Nov 25, 2017 at 14:32