# Simple question on newtons third law of motion

Hey guys, I was just wondering if you could help me with a question that has been bugging me for a while now. Ive thought of many possibilities to the answer yet i still cant find the right one. The question is that, when a fly strikes the windshield of a truck moving at lets say 60km/h, why doesn't the windscreen shatter. The fly would experience a huge force in order to make it travel at the same speed of the truck and according to newtons third law, every action has an equal and opposite reaction. Therefor, wouldnt that huge force on the fly cause a huge reaction on the glass, hence shattering you?

Any assistance to this question would be most appreciated.

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Doc Al
Mentor
While it's certainly true that the contact force exerted on the fly equals the force exerted on the windscreen (thanks to Newton's 3rd), why assume that a force that would splatter a fly is sufficient to shatter a windscreen?

I think that you are confusing the force on the fly (tiny) with the effects of the force (huge acceleration, thus squish). The windscreen area the fly hits depresses a tiny bit to provide this tiny force.

Dale
Mentor
Hey guys, I was just wondering if you could help me with a question that has been bugging me for a while now. Ive thought of many possibilities to the answer yet i still cant find the right one. The question is that, when a fly strikes the windshield of a truck moving at lets say 60km/h, why doesn't the windscreen shatter. The fly would experience a huge force in order to make it travel at the same speed of the truck and according to newtons third law, every action has an equal and opposite reaction. Therefor, wouldnt that huge force on the fly cause a huge reaction on the glass, hence shattering you?

Any assistance to this question would be most appreciated.