Brain teaser question....

[StrangeRanger]

OK, the basic laws of physics state that for an object to change directions it must either curve/turn or stop and reverse direction. So here's the question: If a bug is heading south on I89 hits and sticks to the perfectly verticle windshield of a truck headed north on I89, did the bug stop to change its direction? Assuming it stuck instaneoulsy and did not curve or slide up or down on the glass.
j

 

[DAM]

the law states:


an object will remain in motion unless acted upon by another object of similar or greater mass...



something like that, i think its newtons 2nd law.




dam()

 

[unxpurg8d]

yep. You said it had to reverse direction. That doesn't mean "turn around". It stopped. Just not voluntarily.

 

[thebestMAX]

I dont know the answer to that but I do know what the last thing was that went through the bugs mind.

 

[troglodytis]

simple answer:
the bug stopped.

it just accerated in the other direction so quickly that it's didn't stay sopped for very long..a split second. draw a graph that plots the bugs velocity. you could orient the graph so that the bug's velocity is on the x axis only. in order to go from 1.5ms to -m/s, opposite direction, it would have to go through zero.


nonsimple answer.

the bug was never traveling in a striaght line..thus it's direction was changing the whole time.

 

[iamwiz82]

i believe it does stop. Dont all things have to have 0 velocity to change direction?

 

[SmiZ]

iamwiz82:

For linear motion, this is true. For simplicity I would assume linear motion in this case.

 

[Pretender]

sure, the split second the fly hits the windshield, it's momentum (p = mv, p:momentum, m:mass, v:velocity) and the momentum of the truck collided, and as the momentum began to transfer from the truck to the fly (law of conservation of momentum, and also it's a non-elastic collision), there had to have been a moment where the fly's velocity was 0.

If we call the truck's velocity X, the fly's velocity V, their masses A and B respectively, and the final velocity of the two combined Z, the following equation shows the result:

Momentum(fly, initial) + Momentum(truck, initial) = Momentum(truck+fly, final)
AV + BX = (A+B)Z

now we're looking for when V=0, so
AV = (A+B)Z - BX

V = ((A+B)Z - BX)/A
and since V=0,
(A+B)Z-BX = 0
A



Any questions?

 

[StrangeRanger]

a couple of you have said that it stopped to change direction. how could it have stopped? if they truck is moving, how/when did the fly stop when it contacted the windshield?
j

 

[Demon-Xanth]

Compressability/malleability of the fly's body and the truck provided the "split second" that the momentum was 0

 

[Viper GTS]

StrangeRanger...

By definition there HAS to be a point where it was perfectly stopped. Let's say for the sake of argument that the bug & the truck were going the same speed, say 20 m/s. We'll also assume linear motion, to keep things simple. A graph of time & velocity would result in a nice flat line at v = 20 m/s. Some time shortly after t = 0 (time of impact), the bug was headed the opposite direction at 20 m/s (assuming negligible impact on the velocity of the vehicle), so relative to it's initial velocity the new motion can be graphed as v = -20 m/s. Obviously your graph will look something like:

-----_____

The problem is that nothing in real life changes instantaneously. The now splattered bug's velocity is a continuous function, & thus had to pass through zero at some point.

Viper GTS

 

[Missus]

Bug goes SPLAT!!!!



Then he goes in all directions... Smear...

Yummy!

 

[gittyup]

If a bug is inside your car while going 65mph on the highway. Is the bug flying at 65mph??

 

[Shalmanese]

Newton's 2nd law:

any object acted upon by an unbalanced force must either speed up, slow down or change direction.

The bug will have a speed (not velocity) of 0 if we only allow it to move 1 dimensionally but if we expand the dimensions, it could kepp at a constant, non-zero speed but have a change in velocity



<< If a bug is inside your car while going 65mph on the highway. Is the bug flying at 65mph >>


ahh.. relative to what, to the bug, it is stationary unless acted upon by a unbalanced force (acceleration, gravity etc) to the observer outside the car, the bug is moving at 65mph(well actually slightly less due to special theory of relativity) while the observer is stationary.

aint relativity a grand thing.

 

[SpongeBob]

gittyup-depends on the frame of reference, if from outside of the car, yes, if from inside of the car, no.