this post was submitted on 05 Nov 2025
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Explain Like I'm Five
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Imagine slamming on the gas in your car. The car lurches forward, pushing your seat into you, and you start to accelerate forward.
As the driver, though, you feel like you are being pushed back into your seat, though it's pretty obvious that there is no force pushing you back, it's just the inertia of your body trying to stay put.
The only force in that system is the force of the car accelerating you forward, and the feeling of being pushed backwards is a fictitious force.
It's the exact same with rotational motion, just trickier to wrap your head around. If you have acceleration, you know there are unbalanced forces, and an object in orbit is constantly accelerating.
This.
Ficticious force doesn't mean that it doesn't act like a force. From the frame of reference of the car, it totally liiks like there's a force pushing you into the car seat, and as a passenger in the car, there's no way to judge from the acceleration alone whether the car accelerated or the Earth's gravity field changed.
Or to put it differently: it feels identical to stand in a space ship accelerating upward at 1G and standing in the same space ship while it's parked on the surface of Earth.