Re: Acceleration and curves

[Hugh Haskell <haskell@ODIE.NCSSM.EDU>]

> just had a non-science type friend ask about the arrow fired
> backwards at 75 mph from a forward moving 75 mph truck  -- what
> would person stationaly on ground at point of release see
> any easy ways to explain this?

The person standing on the ground (that is, who is observing the
vehicle passing at 75 mph, would see the arrow fall to the ground at
0 speed. This is a technique that has been used by the US Navy for
many years to put objects in the water at the point of release from
an airplane flying overhead. In anti-submarine warfare, one wants to
get listening devices into the water that can be used to localize the
enemy submarine. In order to do this the exact location of the
listening device (called a "sonobuoy") must be known. Since an
airplane flying at 100-200 knots would allow the sonobuoy to hit the
water some distance from its release point, a device called a
retro-ejector was developed that fired the sonobuoys backwards at the
same speed the airplane was flying. Thus the sonobuoys having 0 speed
relative to the water (assuming negligible wind speed) fell straight
into the water and it was only necessary to note the position of the
airplane at release to know where the sonobuoy was.

Hugh


Hugh Haskell
<mailto://hhaskell@mindspring.com>

Let's face it. People use a Mac because they want to, Windows because they
have to..
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