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October 2001

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Subject:
From:
"Hiteshew, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 10 Oct 2001 11:57:12 -0400
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I fowarded this question to my physics instructor, Dr. Robert Sopka;
here's his response:


This is a collection of different quantities leading to one of those
"oranges-and-apples" problems. So let's try to sort out what's what!

Ok, here we go....

The term "g-force" is an unfortunate ambiguity often used by engineers. "g"
is the ACCELERATION due to gravity, and if one is, for example, subjected
to 3 g's, that means an ACCELERATION of 3 times 9.8 m/sec^2. Recall that
the acceleration due to gravity is the rate at which gravity changes the
velocity of a falling body.

Now we come to FORCE. Newton says that F=ma, i.e. a net force acting on an
object produces an acceleration in proportion to that object's mass. So
FORCE is related to ACCELERATION, but they are not the same thing! To get a
10 kg object to experience a 3 g acceleration requires twice the force that
a 5 kg object needs. Note that "kilograms" is a unit of mass -  a measure
of the amount of matter in an object, whereas "pounds" is a unit of weight
- the force that gravity exerts on an object.

So to try to put it all together, if an object experiences an aceleration
of 3 g, one needs to know the mass (perhaps in kilograms) in order to
compute the force (F=ma). That force can then be converted to units of
pounds, upon looking up the appropriate conversion factor in your physics
book.

This is a good example of what happens when we get sloppy with definitions!

See ya....

Sopka
-----Original Message-----
From: Jason Gregory [mailto:[log in to unmask]]
Sent: Tuesday, October 09, 2001 12:01 PM
To: [log in to unmask]
Subject: [TN] 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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