Why Doesn't a Windshield Shatter When a Fly Hits It at High Speed?

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Discussion Overview

The discussion centers around the question of why a fly does not cause a windshield to shatter when it strikes the glass at high speed, specifically in the context of a truck moving at 60 km/h. Participants explore the implications of Newton's laws of motion, particularly focusing on the forces involved in the collision and the resulting effects on both the fly and the windshield.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the assumption that the force sufficient to splatter a fly would also be enough to shatter a windshield.
  • Another participant suggests that the force on the fly is small, and the windscreen only depresses slightly upon impact, which limits the force transmitted to the glass.
  • A different view emphasizes that the situation is more about the fly's large acceleration due to its small mass, leading to a moderate force that is not enough to shatter the glass.
  • There is a reiteration that the mass of the truck is significant, meaning the moderate force from the fly's impact does not substantially affect the truck's motion.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the forces involved in the collision and the resulting effects on the windshield. There is no consensus on the explanation, as various aspects of Newton's laws are interpreted differently.

Contextual Notes

Some participants note that the discussion involves assumptions about the forces and accelerations at play, and the specific definitions of terms like "force" and "impact" may influence the interpretations presented.

sanado
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Hey guys, I was just wondering if you could help me with a question that has been bugging me for a while now. I've thought of many possibilities to the answer yet i still can't find the right one. The question is that, when a fly strikes the windshield of a truck moving at let's 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, wouldn't 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.
Thanks in advance
 
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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.
 
sanado said:
Hey guys, I was just wondering if you could help me with a question that has been bugging me for a while now. I've thought of many possibilities to the answer yet i still can't find the right one. The question is that, when a fly strikes the windshield of a truck moving at let's 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, wouldn't 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.
Thanks in advance
This is actually a 2nd law question, not 3rd law. The fly experiences a very large acceleration, but since its mass is very small by F = ma you get a moderate force. The reaction force is equal and opposite, so it also is moderate and therefore not strong enough to shatter the glass. Also, since the mass of the car is so large the moderate force doesn't decelerate it very much at all.
 

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