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# Common sensible definitions & equations

## Common sensible definitions & equations - Physics Forum

### Common sensible definitions & equations - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#1
09-08-2005, 01:40 AM
 Don1 Guest Posts: n/a
Common sensible definitions & equations

THE FOUR BASIC EQUATIONS DON WILL NOT LEARN!

1. v = a * t
2. s = 0.5 * a * t^2
3. F = dp/dt = m*dv/dt = m*a
4. 1/(x/y) = y/x

Don prefers to make up his own definitions and equations, and modify
them as necessary:

Velocity (v) is an inertial displacement; an inertial rate of change
in a body's relative position, during time (t); where the change in
position (l) proceeds at a uniform speed, in an unchanging direction.

Velocity can be graphically depicted with a straight line vector whose
length (l) represents the distance displaced, and its direction
represents the direction of the inertial displacement:

v = l/t
o---------------------->

Forced displacement is a forced change in a body's relative position;
due to a net force, acting on and/or by it during time; where the
change in position proceeds depending on the magnitude, and direction
of the force, and the body's inertia; where its inertia is the ratio of
the force required to the rate of displacement caused.

Forced displacement can be graphically depicted with a curved line in
the direction of the impressed force; whose length (s) is proportional
to the magnitude of the force, and its duration (t).

Where the resultant displacement (d) is the algebraic sum of l, and s.

v = l/t s
o----------------->------------------>
<<------------ d ----------------->>

Something like that anyway.

Don

#2
09-08-2005, 02:32 AM
 odin Guest Posts: n/a
Common sensible definitions & equations

> THE FOUR BASIC EQUATIONS DON WILL NOT LEARN!

Wow... a Don1 that is actually more boring than the original Don1!

#3
09-08-2005, 03:15 AM
 Sam Wormley Guest Posts: n/a
Common sensible definitions & equations

Don1 wrote:

*Plonk*
#4
09-08-2005, 05:51 AM
 Jim Black Guest Posts: n/a
Common sensible definitions & equations

Don1 wrote:

So according to Don, is 1/(x/y) = y/x, assuming x and y are nonzero a
true statement or not? Or is Don a constructivist, giving the
statement neither truth nor falsehood, since he cannot determine for
himself whether it is right? What are the axioms of Don's mathematics?
Does Don believe in division of numbers, i.e.,

for all real numbers x and y, other than y = 0,
there is one and only one real number,
called x/y, such that
x = (x/y)*y ?

Does Don believe division is no longer possible when the quantities in
question have units? Or is there some other postulate of normal
mathematics that Don does not accept? What would Don say about the
following reasoning?

1) x = (x/y)*y Def. of division
2) y = (y/x)*x Def. of division
3) y = (y/x)*[(x/y)*y] Substitution of (1) into (2)
4) y = [(y/x)*(x/y)]*y From (3), via associative property
5) (y/x)*(x/y) = y/y From (4), via def. of division
6) y = 1*y Identity property
7) 1 = y/y From (6), via def. of division
8) 1 = (y/x)*(x/y) Combination of (5) and (7)
9) 1/(x/y) = y/x Def. of division

There's the associative property in there. What does Don think of the
associative property? Or is it some other postulate Don has a problem
with? Tell us, Don, about Don's new mathematical system.

#5
09-08-2005, 09:42 AM
 tadchem Guest Posts: n/a
Common sensible definitions & equations

"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

As soon as you improve something and make it foolproof, the world makes an
improved fool.

Tom Davidson
Richmond, VA

#6
09-08-2005, 02:52 PM
 odin Guest Posts: n/a
Common sensible definitions & equations

> Now, we have v=l/t, and s=(g/2)t; so that d=l+s: Instead of y/x = mass

Only fools would bother to make the obvious point that w=(w/g)g and
f=(f/a)a. What are you getting at with this rubbish?

Vectors are not straight lines. A vector has a direction and a magnitude. A
line (in 2D) has a slope and an intercept. NOT THE SAME THING!

No shit sherlock....

#7
09-08-2005, 03:15 PM
 PD Guest Posts: n/a
Common sensible definitions & equations

Don1 wrote:

Get these four down, and I'll feed you four more.

This is feasible, but it presumes some error-checking skill, which you
are rusty at.

This is not required, because something that is in a state of
acceleration (that is, either a constantly changing speed or a
constantly changing direction or both) also has a velocity at every
instant of that motion. The trick is how to define that velocity.
Clearly the definition above does not work.

No, and this is a common mistake. A drawn-straight vector for velocity
does NOT imply that the object will GO straight, or that it will
necessarily cover the distance l in the next t seconds. For example,
something that is traveling in a circle (say, on a Ferris wheel) will
have a velocity vector at any point that can be *drawn* as a
straight-line vector tangent to the circle (so that the point of the
arrow actually lies *off* the circle), but this does *not* mean that
the object will ever go in a straight line.

This is an artificially complex notion. It would be much simpler to
introduce the notion of acceleration, and then ask the question what
causes the acceleration, and what is the relationship between the size
of the cause and the size of the effect.

And this is *clearly* mistaken. The force on an object traveling at
constant speed in a circle is *toward the center* and this is nowhere
near the direction of the curve that the object follows. I can convince
you of this with a rock being whirled around your head on a rope.
Remember that a rope can *only* pull along its length; you can't push
with a rope, nor can you push something to one side, perpendicular to
the rope. If you'd like to examine this in more detail, I can explain
it in more detail.

#8
09-08-2005, 11:17 PM
 Clemens W Guest Posts: n/a
Common sensible definitions & equations

Don, with his bloodcurdling mathematical knowledge, wrote:

which are absolutely wrong 9 out of 10 times.

to introduce even more errors.

This was the most bloviated definition of uniform motion, one of the
simplest physical formulas. You could have saved a lot of bandwidth by
just saying:

s=v*t

Oh, BTW, would you agree that t=s/v is also correct?

Again, bloviated and... BOGUS! Not only are you mixing up the concepts
of inertia and mass again (which would be forgivable), but it's
definitely the "ratio of force required to the resulting acceleration",
NOT the "rate of displacement".

Too many words for just saying:

d=(v*t)+(1/2*a*t^2)

Awww, Don, your mental impotence is showing again:

s=(g/2)t^2

NOT (g/2)t

Awww, Don, how many times have I already told you that frequency
divided by acceleration just doesn't make sense?

Awww, Don, back to 1=1 as your greatest achievement?

Awww, Don, vectors may be straight, but they're surely not lines.

Wow, Don explaining infinitesimal calculus in just two lines! Why does
it take a WHOLE YEAR to learn that in school?

Admit it, Don, you never actually had calculus, let alone understood
it.

I bet you cannnot prove that it isn't. As long as w,g <> 0, of course.

Go back to school, Don.

A. Friend

#9
09-08-2005, 11:41 PM
 donstockbauer@hotmail.com Guest Posts: n/a
Common sensible definitions & equations

I feel like a victim of polysemy.

#10
09-09-2005, 08:13 AM
 tadchem Guest Posts: n/a
Common sensible definitions & equations

"odin" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

The point is that to sHead (Don1) this tautology is *not* obvious.

Tom Davidson
Richmond, VA

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