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Let's say we got a toy car equipped with an electric engine.

The engine exerts a force on the toy car and accelerates it when the car is at rest.

Let's say I'm sitting stationary on a bench and I see the toy car start up from rest. From my frame of reference, I observe an acceleration, and a force was exerted.

However, let's say I'm trying to walk in step with the toy car, so I accelerate my myself at the same rate as the car.

From my accelerating frame of reference, the car has no acceleration. However, from my frame of reference, is there still a force exerted on the car? Thanks for the help!

mouldyfart
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3 Answers3

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From my accelerating frame of reference, the car has no acceleration. However, from my frame of reference, is there still a force exerted on the car?

Yes the force still exists and so it would seem that $F\ne ma$.
It is precisely for this reason that fictitious/pseudo forces are introduce so that $F=ma$ is a valid relationship.

In your case you would have $\vec F_{\rm real} +F_{\rm fictitious} = m\,0$ where the two forces have equal magnitudes but act in opposite direction.

Farcher
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To carry out analyses in accelerating reference frames, you must include inertial forces--fake forces that are needed to make the motion of objects make sense. Any real force exists and is the same in all reference frames. In the frame accelerating along with the car, there's an inertial force of equal magnitude to the real force acting in the opposite direction. That's why the car doesn't appear to accelerate.

Ben51
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Acceleration is a frame dependent thing, different observes have different views about acceleration of the same body, but real forces not vanishes as you change the observer they act and show their significance.

When you see the car from outside, you see the car have the certain acceleration just after it start.

When you see the car, while you walk with same velocity just after the car start, you need to include a pseudo force why because you are non inertial observer so situation will $F_{ps} =F_{electric}$, this what you will see about the car

(hence from your point of view car will always have the zero velocity or acceleration. ).

आर्यभट्ट
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