Question about gravity and mass

[Jimdandy]

 

Originally posted by mrfish:
yeah yeah jim    
with rotation i imagine

Yep. The earths rotation can be used to sling shot the rocket into orbit.

Sorry mrfish I added one after you replied.



[This message has been edited by Jimdandy (edited 01-29-2001).]

[-towd_]

niether over the pole , reason shortest path to russia hehe.

[Dux]

I stand corrected  

[Zigrat]

do you want me to scan my notes deriving kepler's laws all from F=ma?


its probably about 8 pages

[Jimdandy]

Dang mrfish I'm got to thinking about this and play with the vectors and I have to make an corrction.

If you had a scale weighed an object at the poles you would get it's true weight Wt=Gmme/R^2. Wt=true weight, G= gravitational constant m= mass of the oject, me= mass of the earth. Now if you went to the equator you would have to take into account the centripetal force mv^2/R. Thus if you stoped the earth we would actually see a small increase in weight on the scale. G is still constant but are wieght at the equator would be slightly more.

 

Originally posted by mrfish:
ok JIMDANDY

since i have already geeked out all day and wasted tons of co. time i think i will take a stab at it:

Picture a spaceship flying over. You can see thru the spaceship. Inside is a clock that counts by bouncing a laser between to pieces of glass. Now trace the path of the laser as the ship flies over head. Which clock is slower retaliative to the observer on the ground the observers or the spaceships.

- the clock on the space ship would seem slow relative to the clock on the ground though each would operate the same in their referential frame (the speed of the spaceship would have been nice)

There is a train traveling at you. Which direction in the light spectrum is the light on the front of the train shifting toward. Which side of the spectrum is it going to if traveling away from you.

- toward the blue end of the spectrum and away the red end

What would happen if the earth stopped rotating. Would we feel a stronger or weaker gravitational pull? What would happen if it spun faster. Would we fly off?

- no gravity has nothing to do with it everything would remian the same (execpt of course weather)
EDIT: oops i meant rotation has nothing to do with it - yes gravity play a small part  

How many licks does it take to get to the tootsie roll center of a tootsie pop.

- 22 1/2
   


[This message has been edited by mrfish (edited 01-29-2001).]

[PakRat]

Dux is Right - sort of! Ellipses are indeed possible, though.

The link HiTech cited is the stating of Kepler's Laws of Planetary Motion.

An ellipse is in fact a conic section - as are circles, parabolas, and hyperbolas.

A useful link:   Newtonian Gravitation and the Laws of Kepler

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Rape, pillage, then burn...

[This message has been edited by PakRat (edited 01-29-2001).]

[Dingy]

 

Originally posted by Ripsnort:
Er, guys, the moon is moving toward earth, and one day, will crash into it,..if memory serves me correct, I think the Discovery channel said something like 10.2 billion years, or something astronomical number...

Correction, see post below...thats the Earth moving towards the Sun?

[This message has been edited by Ripsnort (edited 01-29-2001).]

The moons also getting closer to Earth...by about 8 inches a year.    

-DIng

[Dingy]

 

Originally posted by Jimdandy:
  The max velocity is independent of the mass. You all remember that in a vacuum a feather will fall just as fast as a 1,000lb ball of led. Acceleration due to gravity it just that. It has nothing to do with mass. EVERYTHING in a vacuum accelerates at 32.2ft/sec/sec on earth. It will NEVER reach a maximum speed with out the presence of some drag/force. A body in motion will remain in motion unless acted upon by and out side force. Terminal velocity is what I think your looking for and that is based on drag (the outside force). Everything has a terminal velocity based on it's Coefficient of drag (Cd). For a man it is roughly 160 mph. F=ma a is constant equaling 32.2ft/sec/sec. So to answer your question no it has nothing to do with mass it has to do with the gravitational constant in a vacuum. Put the object in a medium of some kind and you will have to take into account the shape/drag of the object.
B]

OK you were complaining that no one answers you so I will Jim    You are right and maybe a little wrong...

I think you (or maybe I) was getting tied up in your wording.  First acceleration is not a force...it is the result of a force working upon a mass.  It is the change in an objects velocity (a vector quantity) of some object due a force which is being EXERTED upon that object.  I believe that was what you were trying to say?

However, the acceleration (or change of velocity) of two objects via gravity IS affected by mass...since

F(gravity) = Gm(1)m(2)/r^2
and
F=ma

Now what this means is this: the acceleration of objects towards the Earth is around 32 m/s^2 at ground level BUT if you take the same object and try to measure the acceleration towards an object of a different mass, you get a different value.  You also get a different value for acceleration at varying distances from the center of the Earths mass.

Yes this gets confusing and you may have been right, but got caught up in the wording.  Dunno if this makes any more sense  

-Ding

[Dingy]

 

Originally posted by hitech:
And as to your why hasn't the Vel of the moon changed, I submit it is changing constantly, depends if you view Vel as speed and direction or just speed. I've been doing this simming stuff to long, and it is almost impossible for me to view Vel,And force in any other terms than instantaneous vectors.

I do so love this stuff.
On a side note was debating if a circle is an ellipse, I can't remember if an ellipse definition is 2 unique points or 2 points.

HiTech

[This message has been edited by hitech (edited 01-29-2001).]

Love this stuff too    Velocity is a vector sum meaning it has both SPEED and DIRECTION.  So I concur that the velocity of the moon is constantly changing.  

And yes a circle is an ellipse...its just that the two focal points lie on top of one another.

-DIng

[This message has been edited by Dingy (edited 01-30-2001).]

[Dingy]

 

Originally posted by Jimdandy:
If you had a scale weighed an object at the poles you would get it's true weight Wt=Gmme/R^2. Wt=true weight, G= gravitational constant m= mass of the oject, me= mass of the earth. Now if you went to the equator you would have to take into account the centripetal force mv^2/R. Thus if you stoped the earth we would actually see a small increase in weight on the scale. G is still constant but are wieght at the equator would be slightly more.

 

Whoa??  True weight?  What is that?

Weight is nothing more than a measurement of forces upon some mass.  Usually we use weight to indicate the force of gravity upon some mass.  

Because the force of gravity is dependent upon the mass of the object you are measuring, the mass of the Earth (or whatever planet you are measuring on) and the distance the two centers of mass are from one another, you are also going to find different weights for an object depending upon which altitude (distance from the center of your mass from the center of the Earth's mass) you measure at.

You are right tho, the rotation of the Earth does have a minor effect of an objects weight due to centrifugal force (really just a resultant change in an objects rotational velocity).

-Ding

[This message has been edited by Dingy (edited 01-30-2001).]

[Saintaw]

what's wrong with....

Mass ?

[mrfish]

 

Originally posted by Dingy:
The moons also getting closer to Earth...by about 8 inches a year.    

-DIng

i have to disagree based on nasa's laser distance measuring experts as well as satellite observations between 1970 and today - curiously what are your sources?