Further to this, I was looking at this question a few months ago, when
trying to determine the height I needed to drop our product to test the
packaging design. It was supposed to survive a certain G-force.
G-force is related to acceleration as has already been stated. In my case,
I would have needed to know the length of time it took for the object to go
from its falling velocity (easily calculated from the acceleration of
gravity as stated in many of the responses already) to a full stop at
impact, in order to calculate the negative acceleration (the length of time
would have been in the milliseconds). The negative acceleration calculated
is then divided by the standard acceleration of gravity to determine the
'number of G's'.
I soon gave up on calculating this as it was outside my area of expertise
(I'm electrical, not mechanical) and I did not have the instrumentation to
measure the impact time. Luckily, a CM nearby had a vibration table and
some instrumentation that allowed a few reasonable actual measurements to be
taken by a mechanical consultant engineer we hired.
Proper packaging design reduces the number of G's your product experiences
because the cushioning prolongs the time for an object to come to rest from
an impact.
Regards,
Genny.
-----Original Message-----
From: Hiteshew, Michael [mailto:[log in to unmask]]
Sent: October 10, 2001 9:57 AM
To: [log in to unmask]
Subject: [TN] FW: [TN] Question for the physics "gurus"
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]
------------------------------------------------------------------------
----
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
------------------------------------------------------------------------
----
-----
----------------------------------------------------------------------------
-----
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET
Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
----------------------------------------------------------------------------
-----
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
