Walter...
Got it. Thanks !
Gordy
From: WALTER/SUE SIMBIRSKI <simbirsw@xxxxxxx>
To: Gordon Hill <hillshead@xxxxxxx>
Subject: Re: Reading material
Date: Mon, 30 Oct 2006 14:16:32 -0700
Gordy - You should have my email about acceleration and deceleration so we won't worry about that.
Acceleration is indeed a rate of change of a rate of change. When you look at velocity it is usually expressed in terms of some (unit of distance) per (unit of time) (e.g. 32 mph) (i.e. rate of change of distance). Acceleration will be expressed in terms of (unit of distance) per (unit of time) per (unit of time) (e.g. 32mph per hour, or every hour the velocity increases by 32 miles per hour - unless I know the actual velocity of the object at some point in time there is no way to tell what its velocity is at any other point in time, all I know for sure is the difference between the two velocities)
The rocket propelled object off the cliff would probably be experiencing a constant acceleration. For example, if the rocket added another 40'/sec/sec of acceleration to the object then it would be accelerating at a total of 72'/sec/sec. It's still a constant acceleration just a greater amount.
A better example of accerating acceleration would be stepping on the gas pedal of your car slowly. With a lttle bit of pressure the car accelerates slowly. As you add pressure the acceleration increases until you get the pedal to the metal. At this point the acceleration remains fairly constant until the car approaches its maximum velocity.
Walter
From: Gordon Hill <hillshead@xxxxxxx>
To: simbirsw@xxxxxxx
Subject: Re: Reading material
Date: Mon, 30 Oct 2006 15:36:00 -0500
Walter...
I blew the dust off my son's old physics notes and came up with the following definitions...but would like your input.
SPEED : Rate in tilme at which something travels. (I note no mention of direction, so I must assume it is not a vector quantity.)
VELOCITY: The time rate of change of a body in a specified direction.
ACCELERATION: The time rate of change of velocity with respect to magnitude or direction.
(If we go by this, it provides a conundrum since it makes it seem as though we are describing a time rate of change of a time rate of change, here. Something fishy about that thought !)
Your statement, "Whenever you have a change in velocity, you have acceleration" does make sense to me, so long as that change is an increase in velocity.....but what about a change in velocity which is a decrease ? Would that be defined as, "deceleration" ?
Can we not have an increasing rate of acceleration ? For example: An object has a constant acceleration of 32'/sec/sec when dropped from a 1000' cliff. Now, we affix a rocket to it and note that it gets to the ground a lot sooner. Did we have an increase in the RATE of acceleration ? Could we call that, "accelerated acceleration " ???
Just trying to learn !
Gordy
From: Walter Simbirski <simbirsw@xxxxxxx>
To: Gordon Hill <hillshead@xxxxxxx>
Subject: Re: Reading material
Date: Sun, 29 Oct 2006 18:32:42 -0700
Gordy - any time you have motion that isn't in a straight line you have acceleration. The tip of the propellor blade may be travelling at a constantspeed but the direction is constantly changing. Remember that velocity is a combination of speed and direction so the velocity is constantlychanging even though the speed is constant. Whenever there is a change of velocity there is acceleration.By the way - thanks for the feedback on the web site. Simple and easy to navigate is good.ThanksWalter----- Original Message -----From: Gordon HillTo: simbirsw@xxxxxxxSent: Sunday, October 29, 2006 3:57 PMSubject: Re: Reading materialWalter...
Good idea on both counts. I'll check out that website and let you know my thoughts.
On thing, in particular, bothers me about acceleration being unidirectional, linear, and a vector quantity.
How does one explain an airplane engine which starts slow, then spins in a circular manner faster and faster. Does this propeller not accelerate ? It certainly isn't moving in a unidirectional or linear path, but rather a circular one.
Can it be that an engineering way of looking at it is to envisage an infinite number of vectors with a resultant in a circular path ????
Gordy
From: Walter Simbirski <simbirsw@xxxxxxx>
To: Gordon Hill <hillshead@xxxxxxx>
Subject: Re: Reading material
Date: Sun, 29 Oct 2006 10:29:53 -0700
Gordy - I would be happy to put something together. It should take about a week or two. I've been planningon putting together an article on casting physics (simplified) for the Loop. This will give me some incentiveto start sooner rather than later.In the meantime could you take a look at the website I've put together and give me some feedback? I useda program I was able to find on the web to convert the list of emails I have to an archive so the subject listis automatically generated by that program. We could spend some time going through the list to identifythe ones that are most relevant and create an additional, better organized, list from that. I haven't includedemails from the past few weeks - wouldn't take to long to do that at this point - I thought I should get somethingfor people to look at sooner rather than later.The web site is www.snapcasts.comfollow the study group link for stuff related to the study group.ThanksWalter----- Original Message -----From: Gordon HillTo: simbirsw@xxxxxxxSent: Friday, October 27, 2006 8:35 AMSubject: Reading materialWalter...
Many of us non-physics / engineer folks in the Group, have had trouble really coming to terms with the basic understanding of:
1.) Velocity 2.) Acceleration 3.) Linear acceleration as well as terms relating to application of force, torsional and otherwise.
I wonder if you could help us by referring us to some basic texts or other writings which will help clarify these and other physics terms in a way which is not too difficult for the lay person to understand ?
Thanks !
Gordy