From owner-freebsd-hackers@FreeBSD.ORG Tue Aug 23 18:56:39 2005 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 749CF16A41F for ; Tue, 23 Aug 2005 18:56:39 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from mail24.syd.optusnet.com.au (mail24.syd.optusnet.com.au [211.29.133.165]) by mx1.FreeBSD.org (Postfix) with ESMTP id CA2F843D46 for ; Tue, 23 Aug 2005 18:56:38 +0000 (GMT) (envelope-from PeterJeremy@optushome.com.au) Received: from cirb503493.alcatel.com.au (c220-239-19-236.belrs4.nsw.optusnet.com.au [220.239.19.236]) by mail24.syd.optusnet.com.au (8.12.11/8.12.11) with ESMTP id j7NIuZZW018663 (version=TLSv1/SSLv3 cipher=EDH-RSA-DES-CBC3-SHA bits=168 verify=NO); Wed, 24 Aug 2005 04:56:36 +1000 Received: from cirb503493.alcatel.com.au (localhost.alcatel.com.au [127.0.0.1]) by cirb503493.alcatel.com.au (8.12.10/8.12.10) with ESMTP id j7NIuZSR039737; Wed, 24 Aug 2005 04:56:35 +1000 (EST) (envelope-from pjeremy@cirb503493.alcatel.com.au) Received: (from pjeremy@localhost) by cirb503493.alcatel.com.au (8.12.10/8.12.9/Submit) id j7NIuYAt039736; Wed, 24 Aug 2005 04:56:34 +1000 (EST) (envelope-from pjeremy) Date: Wed, 24 Aug 2005 04:56:34 +1000 From: Peter Jeremy To: Borja Marcos Message-ID: <20050823185634.GE37107@cirb503493.alcatel.com.au> References: <200508221720.j7MHKpNb022773@peedub.jennejohn.org> <430B11B0.20702@pacific.net.sg> <200508232155.02444.doconnor@gsoft.com.au> <34E57F6C-EDF8-4E51-86AC-863109217B85@sarenet.es> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34E57F6C-EDF8-4E51-86AC-863109217B85@sarenet.es> User-Agent: Mutt/1.4.2i Cc: freebsd-hackers@freebsd.org Subject: Re: IBM Active Protection System Approach X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 23 Aug 2005 18:56:39 -0000 On Tue, 2005-Aug-23 15:37:49 +0200, Borja Marcos wrote: >>mmm.. There is a static 1G force on the laptop while it is on your >>desk. When >>it falls it goes to 0G as it is in free fall. >> >>Still.. "delta G == park laptop heads" :) > > It's not a "force meter", but an acelerometer. It measures >acceleration. If the computer is sitting on your desk, as it has >already been said, it detects nothing. When falling, the acceleration >is 1 G, ie, 9.8 m/s^2 Actually, it's the other way round. The accelerometer is detecting acceleration within the frame of reference of your laptop. When sitting on your desk (or holding it stationary in your hand), the accelerometer will detect a static 1G acceleration. Whilst your laptop is falling, the accelerometer reads 0G (neglecting air friction) because your whole laptop is accelerating. It might be easier to think of the accelerometer measuring the force exerted by a fixed mass sitting on your laptop. -- Peter Jeremy