B According to Newton's 3rd Law....

[Nugatory]

"The wording is fine and cannot be blamed for your misguided ideas."

Ya that's really constructive.

That’s fair, but I still have to ask: if you don’t like the wording, what might be a better way of stating Newton’s third law?

 

[PeterDonis]

It conjures ideas of the bug hitting your windshield with as much force as the car hitting it - like a head on collision with a car of equal mass, except it's a bug doing it.

But a bug doing it is not the same as a car of equal mass doing it at the same relative speed. That's the whole point. Force is not mass alone, it's mass times acceleration. If a bug hits your windshield, the bug decelerates a lot, but its mass is tiny; the car has a large mass, but a tiny deceleration. The result is a tiny force--the same tiny force both ways.

If, OTOH, two cars of equal mass collide, both of them decelerate a lot. It's the large mass times the large deceleration that makes the force much larger--much larger both ways.

 

[rudransh verma]

@jaketodd The windshield is moving too at 50 mph because it’s attached to the car. So it doesn’t make any difference whether it’s 50 or 500. All that matters is your force on bug which is very less to break a windshield. It’s that simple.
It doesn’t matter if it’s moving car or stationary ground.

 

[valenumr]

That idea was debunked just a few posts ago!

Oh gosh, I can see how this might be confusing the way it is written. I wasn't referring to the collision. I was referring to the properties of the car before the collision.

 

[PeroK]

Oh gosh, I can see how this might be confusing the way it is written. I wasn't referring to the collision. I was referring to the properties of the car before the collision.

A pebble can shatter the windscreen, but it's not going to slow the car down significantly.

 

[jbriggs444]

A pebble can shatter the windscreen, but it's not going to slow the car down significantly.

Spark plug fragments can do a number on the tempered glass in side windows.

As I understand it, tempered safety glass is pre-stressed. All it takes is the creation of a tiny flaw for those stresses to shatter the remainder of the window. The ceramic in a shattered spark plug is hard enough and has edges sharp enough to create such a flaw.

 

[jaketodd]

That’s fair, but I still have to ask: if you don’t like the wording, what might be a better way of stating Newton’s third law?

I really don't know. You guys are the experts, and it seems a conclusion hasn't been reached yet. Maybe Newtons 3rd Law should be introduced or worded with caveats like the ones we see in this thread.

 

[Nugatory]

I really don't know. You guys are the experts, and it seems a conclusion hasn't been reached yet. Maybe Newtons 3rd Law should be introduced or worded with caveats like the ones we see in this thread.

What caveats? The force of the bug on the windshield and the force of the windshield on the bug are exactly equal and opposite with no ifs, ands, buts or other hedging. That has been stated explicitly and repeatedly, starting with the very first reply you received and most recently in posts #47, #48, and following.

All the other discussion has been about why these equal and opposite forces can produce very different impact effects and why you are therefore mistaken to assume from the different effects that the forces are different.

 

[Nugatory]

This thread is closed as the discussion is no longer productive.

As with all such thread closures, if you feel that there is something to say that has not already been said, you can PM me or any of the mentors and we can reopen it for your contribution.