Transcript bug windshield - 3rd law

On the highway
of life, do you
want to be the
bug or the
windshield?
Bug hits windshield
Are the forces equal?
Bug hits windshield
The force on each is…
The same - Newton’s third law.
You can only exert back as much force
as is exerted on you.
If the bug hits the car with 4 oz. of
force, the car can only apply 4 oz. of
force back.
Is the bug’s velocity changed…
Yes - It would be impossible for the bug to hit
the windshield for ½ second while the
windshield hits the bug for ¾ second, so the
same force is applied by the bug back on the
windshield for as long a time.
The change of velocity on each
is…
Very Different – The car, hardly noticeable.
The bug very noticeable. The bug slows
down, stops and reverses direction
Think about it…
• What about a BIGGER BUG?
The force on each is…
Again, the same
But the bug pushes harder now
Newton’s third law You can only
exert back as much force as is
exerted on you
Newton’s third law You can only exert back
as much force as is exerted on you
The change of velocity on
each is…
Slightly Different – The car,
slows down noticeably. On-theother-hand, the bug slows down,
stops and reverses direction
Back to small bug
• So why does the (small) bug go splat, but
a windshield doesn’t?
• What’s different?
• The bug has much less mass and hence
much less inertia.
What if the bug was the same
mass and same speed as a car?
They stop