Re: Calculating Newtons in Joules and Joules/s

Dennis B a écrit :

hhc314@xxxxxxxxx wrote:
Dennis, I tend to believe that the reason you MAY be confused is that
you have never taken the time to understand the underlying concepts of
simple mechanics. You can't acquire this understanding by memorizing a
bunch of equations and conversion factors.

Once you really comprehend Newtonian principles, the equations and
conversion factors become obvious ... i.e. simple fallout from your
comprehension. If you start with the equations first and try to proceed
backwards, you'll likley generate some bizarre concepts which limit
your ability to proceed farther.

The fundamentals of simple mechanics are not real mind benders, and
begin with an understanding of the concepts such as the conservation of
energy and the conservation of momentum. Newton observed that the force
applied to any body of mass (excluding resistance and other secondary
factors) is precisely equal to the time rate of momentum change to the
mass. Newton expressed this as f = dp/dt = m dv/dt + v dm/dt. When
mass is constant, this simplifies to f = ma.

Similarly, energy = work = f x s (where s is the distance through which
the force is applied)

Also, force applied for a period of time to a unconstrainded body of
mass is termed IMPULSE. Impulse is precisely equal to the change in
momentum of the mass.

Momentums is mass x velocity = mv
Energy is mass x velocity squared = mv^2

I realize that this makes little sense until you understand the physics
concepts involved, and from that how to derive these relationships.

This is why I would suggest the purchase of a good Physics 101 text as
the first step to understanding these fundamental concepts in physics.
(Halliday and Resnick is excellent, but I still prefer Sears and
Zemansky.) Since this stuff has not changed during the last 100 years,
used copies at prices from $5 to $20 each are preferable to brand new
copies at close to $100 each.

Just a suggestion, and I sometimes tutor college students in physics
basics, even though my pincipal field is theoretical mechanics and
electromagnetic field theory.

Harry C.

p.s., Experience of my students has taught me that you likely won't
learn much physics if your only source is coffee table books from
Barnes and Noble, or web sites.




Dennis B wrote:
Dennis B wrote:
hhc314@xxxxxxxxx wrote:
Dennis B wrote:

Does anyone know how to convert Joules into Newtons and
Joules-per-second into Newtons-per-second?
Dennis B wrote:

Dennis, no such conversion exists, because the Joule is a unit of
energy and the Newton is a unit of force.

The closest you can come it to assocate them in terms of some physical
relationship equation that will always employ other additional
parameters such as distance, time, potential, etc. For example:

1 Joule = 1 Newton-Meter

Harry C.
I believe Joules are actually a measure of total Newtons exerted across
a distance. When you multiply Newtons by the total distance, what you
are doing is multiplying the Newtons (exerted per meter) by the total
meters traversed so as to calculate the total Newtons exerted. For
example if you multiply 2 Newtons by 50 meters, the total Newtons
exerted will be 100 Newtons (2 Newtons * 50). This is proven by the
following equations:

F = N = w/d = Joules/meter

Key:

F = Force
N = Newtons
w = work
d = distance

The question is: What is the value of "d"? Should it be 1 meter (in
other words, Joules PER METER) or the total distance traversed?

Note that F = w/d. Therefore, if "d" should be 1 meter, then:

100J/1m = 100 Newtons

Key:

J = Joules
m = meters

If it should be the total distance (50m), then:

100/50 = 2/1

100J/50m = 2J/1m

100J = 2N * 50m = 100N/50m

2J = 2N * 1m = 2N/1m

In other words, the unit of J (Joules) would be nothing more than a
unit designating total Newtons exerted across a distance (J = N * d).

Therefore, Joules/second would actually be Newtons/second.
-Dennis B
If I am confused it is because I do not know the time involved. For
example, how much time does it take a 1kg mass to traverse a distance
of 50 meters with an input of 1 Newton? 50 seconds? What if the input
force were 50 Newtons? 1 second?

-Dennis B

I can understand why you would be inclined to conclude I haven't yet
acquired a basic understanding of the principles where physics is
concerned. You would be correct to say that I a have much yet to learn.
Although I understand many of the basics such as the conservation of
energy and momentum, I am confused about the details of acceleration
and inertial force. For example, I am not sure if a force of 1 dyne
will even begin to acclerate 1 cm^ of mercury? In other words, is 1
dyne sufficient to overcome the inertial force of the 1 cm^3 of
mercury?

Furthermore, I have been presenting erroneous equations. Nevertheless,
I worked out the equations until I understood. Please forgive me for
attempting to refine my math skills aloud. Have you read my last
formula? I believe it makes more sense than any other I have seen:

W = N/m * d

Alas, I believe that many of the obstacles which impede my
understanding of physics are actually flaws in the traditional
understanding. Not that the conventional W = N * d (and such) is wrong.
Rather, I believe it is incomplete and misleading. The same applies to
Bernoulli's principle (which I have addressed elsewhere on this forum
only to be labelled a "crank"). It isn't wrong. It is inappropriately
applied and incomplete (in it's pure form), in that it does not apply
to viscous fluids. Rather than allow such obstacles to become
impediments to my understanding, I utilise the challenge to develop a
better understanding.

-Dennis

I think you should first follow Harry's suggestion. The two refs
he proposed are among the best if not the best around. From them
you will learn enough to be able to coherently discuss on the
newsgroups with less chance of being labelled a crank.

André Michaud
.

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