Yes height does matter. Neglecting that an object can reach a terminal
velocity, due to its shape(ie a leaf or a feather will only fall so fast no
matter from how high it falls).
An object free falling 15m will be falling for 1.24 seconds (d=v*t or
=a*t*t, a=9.8, solve for t). At the end of 1.24 seconds, the velocity it is
travelling is 1.24*9.8= 12.15m/s. If it impacts the ground and comes to a
complete stop in 0.5 seconds (a long time to reach full stop), its negative
acceleration is 12.15/0.5=24.3m/s/s. Divide that by gravitational
acceleration, 24.3/9.8=2.48 or the object was subject to ~2.5 "G".
If it falls further, or has additional forces acting on it, like a jet
engine that will increase the acceleration rate, its velocity at point of
impact can be much higher, and the quicker it comes to a stop, (negative
acceleration) the higher the G force. It's the change in velocity that does
the damage.
-----Original Message-----
From: Ken Patel [mailto:[log in to unmask]]
Sent: October 10, 2001 4:29 PM
To: [log in to unmask]
Subject: Re: [TN] Question for the physics "gurus"
All,
If G force is the gravitation force acting on the object then why many times
an object is
being designed to take so may G forces. What I have heard that voice
recorder of the plane
that went down in Pennsylvania can take on 700G force! So, if the free fall
is 1 G then why
design 700 times safer. So, height above the ground does matter. May be I
got to take a look
at the physic's book unless someone explain in layman's term.
re,
Ken Patel
Timothy Reeves wrote:
> No Jason,
> I am not a guru, but that's OK. They are not interconvertible. One is a
> measure of force, the other acceleration (actually a dimensionless
> multiplier of the standard gravitational acceleration, g, 9.8 m/s^2). If
you
> have an object in mind of a known mass, you could find the force exerted
on
> it given the acceleration ("G's") by F = m a.
>
> Example: 100 gram object subjected to 5 G's ---------> F = 0.1 kg * 5 *
9.8
> m/s^2 = 4.9 Newtons or 0.5 kilogram force or 1.1 lb-force.
>
> Tim Reeves
>
> -----Original Message-----
> From: Jason Gregory [mailto:[log in to unmask]]
> Sent: Tuesday, October 09, 2001 9:01 AM
> Subject: Question for the physics "gurus"
>
> How do you convert pound/kilogram to G-force? Is this convertable? Since
> G-force is somewhat time derived and pound/kilogram is force derived?
> Any help is appreciated.
>
> Jason Gregory
> Software Specialist - NPI Group
> SCI Systems/Plant 2
> 13000 S. Memorial Pkwy.
> Huntsville, AL. 35803
> (256) 882-4107 x3728
> [log in to unmask]
>
>
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