physics

[gwynn]

ok, so a longbow arrow travels about 90 mph
you're in a car standing up through the sun roof. the car is doing 90 mph.
shooting forward the arrow will be doing, in theory, 180 mph, but its speed will drop off really quickly due to wind resistance.
now....
you turn around and shoot backwards. does the arrow do anything? it will appear to be going away from you but is that because you are in the car moving away from it at 90mph? it is actually moving backwards when you loosed, does its forward speed negate its backwards motion? logic says it must move. got to try this!
just something we started debating in the woods today.
ideas/answers anyone?

[Dave]

I've been thinking about this one for about 6 months and I'm considering getting in touch with Brainiac to# see if they'd be up for trying it

[gwynn]

ja, what you need is an observer on the side of the motorway and you loose backwards just as you get level with him. dont think motorway coppers [or the driver in the car behind you!] would be too supportive though. but im willing to try in the interests of science and the advancement of knowledge

[Furface]

Shooting forward i suspect you would catch the blighter up (which is why modern aircraft fire rockets rather than guns). Firing backwards I'm not sure, but I suspect that the arrow does not have much forward motion per se so would simply go away from the point of firing at 90mph, and put distance between you and it at 180mph. Or should we be imagining the enemies of the Parthians simply riding into a host of apparently motionless arrows, and dying with the words "Oh Bu**er" on their lips? Isn't this related to why it would be futile to jump as the falling lift hits the ground?
(PS - I gave up Physics at 14 to study Greek. No regrets.)

[TJ Mason]

Shooting backwards, the arrow would have a 90MPH tailwind. So add that to the speed that it leaves the bow at, and you (might) get 180MPH.

I say "might" for several reasons:
1. Arrows are drag-stabilised projectiles. A tailwind that strong could stuff up the drag stabilisation.
2. There'll be a load of turbulence from the backwash of the car. Results unpredictable -- turbulence has baffled some of the best minds.
3. The arrow won't necessarily catch all the force of the tailwind, so it could be a lot slower than 180MPH.

Hmm, only one way top settle this... But not on the M62 please when there's a red Renault Clio behind you!

[clickerati]

Can someone pass the paracetamol...my head hurts!#

[TJ Mason]

Gahhh! My head hurts too...

Right, I think I've figgered it out.

In a vacuum, an arrow shot backwards at 90MPH from a car doing 90MPH would appear to travel at 90MPH away from a viewer in the car. But to a viewer at the roadside, the arrow would just drop to the ground -- the velocities would cancel each other out.

But add in the air, and the arrow starts with a 90MPH tailwind. So to an observer in the car it would appear to travel away at 180MPH. But a viewer at the roadside would see the arrow travel at 90MPH.

Strewth. Einstein got public acclaim and prizes for this stuff. Where's mine?

[Barry C]

Einstein said that the laws of physics must be the same for all observers moving at a#constant velovity. Ignoring wind, an arrow shot from a car moving at any speed would look to an observer in the car exactly the same as an arrow shot standing still on the road, by an observer standing on the road. Not sure that helps but its true. </p>



But of course if you shoot Samick extremes you might want to factor in reletivistic effects </p>

[Furface]

Surely there is no tailwind, as that is simply an effect ofn the car moving forward. However, the arrow is travelling at 90mph relative to the moment at which it left the bow, which means that, to the observer at the side, it would appear - as it really is - as travelling at 90mph.
Einstein uttered a load of unprovable tosh. He postulated something involving the speed of light, and then added the speed of light into his famous equation simply to "prove" his original idea

[Barry C]

Einstein uttered a load of unprovable tosh. He postulated something involving the speed of light, and then added the speed of light into his famous equation simply to &quot;prove&quot; his original idea

</p>

Please dont diss the great man. Relativity HAS been proven and a trillion experiments to disprove it have all failed. Have you ever sat a relativity course? I think not...</p>