Re: Calculating Newtons in Joules and Joules/s



Randy Poe wrote:
Dennis B wrote:
How would you define gravitational potential in the case of a mass
SUSPENDED above the Earth???

I would define the gravitational potential of a mass at distance
r from the center of the earth as -GM/r, where M = mass of
the earth. I would use this whether the mass was suspended,
falling toward the earth, in orbit around the earth, or on
a rocket heading away at escape velocity.

Yet, gravity is only a potential when it is not actually inducing an
acceleration.

The term "gravitational potential" doesn't mean "a potential
for causing an acceleration". It refers to a specific physical
quantity.


That physical quantity is the energy associated with the acceleration
of a mass which would POTENTIALLY result.

The term "gravitational potential energy" means the energy
that it would take to move a particle from where it is now
to some reference point (usually infinity, sometimes the
surface of the earth).

The amount of energy that it takes to move a mass in oppositon to
gravity depends upon the velocity of the mass (in other words the time
involved) as well as the strength of the gravitational force. Potenial
KE = 1/2mv^2. The greater the velocity, the greater the energy, and the
greater the distance it will traverse. Converesely, the velocity and
kinetic energy of gravitationally induced acceleration depends upon the
position of the mass from the center of gravity (as well as the mass)
of the gravitating body (ma = mg = GMm/r^2).

Relative to infinity it is -GMm/r.
It has nothing to do with what state the mass m is in,
merely its distance r.


You mean r^2, right?

The term "gravitation potential" means the potential energy
per unit mass. Relative to infinity, it is -GM/r.


Presuming you mean r^2, that is what I am saying as well.

So as I said, you are not using "gravitational potential"
or "potential energy" in the standard ways.


Yes, I am. I am attempting to elucidate what is actually meant by
"potential". When you calculate gravitational potential, you are
calculating it's potential to accelerate and not necesarily an actual
acceleration, although you may use an actual acceleration to measure
the gravitational force so as to determine the strength of it's
"potential" to induce an acceleration.

What is truly interesting is that it is only when the
gravitationally induced acceleration is opposed that the inertial
forces normally associated with acceleration emerge.

I have no idea what you mean by that.


I mean that you feel no inertial forces as you accelerate in
gravitational free-fall (you feel weightless). You only feel (an
inertial) force when you interfere with gravitationally induced
acceleration, such as when you hit the ground after falling from a
height.

- Randy

-Dennis

.

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