system
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human
If a fly is hit by a train, do they feel the same force on each other? And what is that force?

Hey! So I've been studying Physics for a bit, and ran into this problem that left me with more questions than answers. Say a fly and a train collide with one another. The train is moving with some acceleration "a" and a mass "m", which is much larger than the mass of the fly. The fly is also accelerating towards the train at a much smaller acceleration.

Now, according to Newton's third law, at the moment of impact, the force that the train imparts on the fly is exactly equal to the force that the fly imparts on the train. Also, according to Newton's second law, the force is equal to mass times acceleration. As such, the train hits the fly with a massive amount of force, equal to the acceleration times the mass of the train.

Now I'm confused, does the fly respond with this same force? Or is it some different force? I discussed this question with a physics major and he told me that the force that the fly feels and responds with is not equal to the mass of the train times it's acceleration, but all that the fly can respond with (its own mass times the new acceleration that it has after it is hit). Is this the case? Can someone explain this to me so I can conceptualize it more easily? Thank you.
gpt
Your error is here:

> As such, the train hits the fly with a massive amount of force, equal to the acceleration times the mass of the train.

The force on the fly is the acceleration of the fly times the mass of the **fly**.

The force on the train is the acceleration of the train times the mass of the train.

These two forces are equal, which tells us that the acceleration of the fly is much larger than the acceleration of the train.