Question about gravity and mass

[fscott]

If you answer this then you will help me understand the factor of weight pertaining to a plane's ability to dive and maximum dive speeds.

I understand that gravity on earth is 32 ft/sec.  Ina vaccum all things will fall at this equal rate. But my concern is weight.  Does an object continue to fall at a faster and faster rate in a vaccum? For instance, is there a maximum attainable speed based on an object's mass?

Simplify this. The moon is determined to be falling at a rate of 1/20 inch per sec. If it is continuing to fall at this rate, why doesn't it speed up and eventually hit the earth since space is a vacuum? Am I correct that the moon's mass has determined a maximum attainable rate of fall?

Again, only need one question answered ---> Will an object reach a maximum speed in a vacuum based upon it mass?

fscott

[fscott]

---> Or will it fall faster and faster and faster until it hits something or reaches an infinate speed?

fscott

[AKSeaWulfe]

I do not believe the moon is capable of gaining more speed at it's rate of descent to earth, because at the current stage in human evolution it is impossible for a human to bend over and kiss his bellybutton goodbye.

;-)
-SW

[fscott]

The reason I ask, and how it pertains to a plane's ability to dive: If we had a zero drag aircraft, I am wondering how weight would play a factor in it's dive? It seems that in a vaccum, weight would play no role in an object's acceleration in a dive. However, I am assuming that weight would play a role in an objects maximum attainable rate of fall, or maximum mph.

However, when thrust is added into the equation, weight then becomes a factor?

fscott

[hitech]

Acctualy the moon is falling at a rate of about 750 mph it just happens to be moving sideways at 2300 mph so it keeps missing the earth.

To answere your question yes it will keep accelerating  at the same rate regardless of mass. Until light speed effects kick in.

To put it in a math perspective for you.

Force = Mass * Acceleration

Force would be the wieght of the object.

Velocity = Acceleration * Time.
Distance = Velocity * Time
Distance = Acclerations / 2 * Time * Time

HiTech

[hitech]

Your question is fairly simple fscott add up the total down forces which would be Weight + Thrust , now subtract out the current drag of the plane. The acceleration can be computed by the first equeation.

HiTech

[fscott]

HiTech stated:

"To answere your question yes it will keep accelerating at the same rate regardless of mass. Until light speed effects kick in."

Ok, then tell me why the moon does not speed up it's rate of falling to the earth? It is in a vacuum. If it continues to fall at a faster rate, then I would assume it would also have to keep speeding up sideways to prevent hitting the earth. We know the moon is not falling faster, so my question is why isn't it falling at a faster and faster rate until as you say hits the speed of light?

fscott

[fscott]

Forward momentum has no effect on an object's rate of descent. So what keeps the moon from falling faster and faster and faster. I would assume it's mass keeps it at a steady maximum rate of fall?

fscott

[hitech]

Because the 1/10 inch your refering to, not sure if that number is correct, is do to the fact that the moon is slowing down in it's orbit priamarly do to the energy lost creating tides.

HiTech

[hitech]

Best way to picture orbital effects is visualize bullet drop, Now what would happen if you shot bullet fast enough,(assume no drag) so that its arc of drop would = the curvature of the earth. Note the bullet is constantly accelerating to the earth.

HiTech

[mrfish]

start by seperating weight and mass - weight is a result of gravity on mass - mass is harder to define

the answer to your question involves newtons 2nd f=ma

all objects regardless of mass are accellerated at the same rate due to gravity - which as you mentioned is 32 feet per second - except that value is squared

you have to take into account wind resistance in this example though because you are on earth and it is a real factor when dealing with planes in a dive - because as the body accellerates it experiences more wind resistance until it finds equalibrium - the concept is called terminal velocity - a heavier object(more mass) might accelerate toward the earth faster initially due to its ability to negate some wind resistance ....maybe thats what you are looking for i dont know. does that anwser it? if not lemme know

[AcId]

I think I'll insert a little here......"Why isnt the moon accelerating to light speed to crash into the earth?" You have to think of all the forces acting on the moon, not just the earths gravitational pull, How about the force generated buy the moons own mass in traveling an orbit (centrifugal force), this would counter-act some of the earths G-force that is acting upon it, as well as the C-force of traveling around the sun (although probably negligable in this case). You also have to take into consideration on top of all this the relationship of the masses involved to the forces exerted, in our case the moon isn't going to hit us anytime soon, it would take alot more force and distance to get that sucker moving at an even remotely acceptable speed.

Or maybe I'm just crazy.

[mrfish]

 

Originally posted by AcId:
How about the force generated buy the moons own mass in traveling an orbit (centrifugal force)

i think that is correct except i believe the force would be centripetal - since centrifugal force is really kind of illusion of the angular momentum caused by a center seeking object - dont forget the earth isnt just attracting the moon it goes both ways - F=g(m1)(m2)/r sq.

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

[AcId]

Thats it!!!! centripetal.....i forgot what it was and just used centrifugal.  

My brain hurts now.

[Dinger]

Here's how it works according to my limited understanding.  Everything in the universe exerts a gravitational force on everything else; this force is a function of the mass of the subject (the exerter) and the distance to the object (and I imagine it ain't a linear relationship.  I have no idea what the equation is, but it'll probly be along the lines of accel=mass/distance^3; someone correct me please. edit: better yet, just steal MrFish's calcs).  The mass of the object here is irrelevant: a cruise ship full of overweight retirees and a baseball will -- if held at the same distance to the earth's center -- accelerate towards the earth at the same rate.
This is the reason for the apocryphal story of Galileo dropping two weights from the leaning tower of Pisa, and showing how both hit the earth at the same time.

I said the mass of the object was irrelevant; that's true, but you have to understand that the object functions as a subject as well.  So, while the earth has far more mass than the moon, and the moon goes in orbit around it, the earth is being shaken around by the moon's gravity (cf., e.g., tides).

Generally, though, the gravitational measurements we play with involve such disproportionate forces that we ignore one side of the equation as insignificant (even if that cruise ship was serving fried chicken, it still wouldn't move the earth much), and indeed, Kepler's fairly accurate equations for solar orbits do not take into account the mass of the satellites.

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