Astronomy / Space Question about gravity.

  • Thread starter Deleted member 110222
  • Start date

Deleted member 110222

D
If I am on a planet that has exactly half the gravity of Earth, does that mean if I drop a pebble, it will take exactly twice as long to hit the floor? Only the gravity is different. Air type, etc., is all the same.
 

DanGriswold

DanGriswold
Un1k0rn said:
If I am on a planet that has exactly half the gravity of Earth, does that mean if I drop a pebble, it will take exactly twice as long to hit the floor? Only the gravity is different. Air type, etc., is all the same.
Click to expand...

I would think that a little more needs to be factored in than simply the amount of G. The effects of gravity will increase or decrease depending on how close to the center of the massive body you are. So, for example, the gravity of the planet may be half that of Earth, but it may be twice the size of Earth. You, being on the surface, would be further away from the planets center and the effects of gravity may be lessened.

I'm no physics expert, so I may very well be wrong. We need Neil deGrasse Tyson in here to answer this one, or maybe David Braben?
 

Deleted member 110222

D
DanGriswold said:
I would think that a little more needs to be factored in than simply the amount of G. The effects of gravity will increase or decrease depending on how close to the center of the massive body you are. So, for example, the gravity of the planet may be half that of Earth, but it may be twice the size of Earth. You, being on the surface, would be further away from the planets center and the effects of gravity may be lessened.

I'm no physics expert, so I may very well be wrong. We need Neil deGrasse Tyson in here to answer this one, or maybe David Braben?
Click to expand...

As said, only the gravity is different in my hypothetical'. Literally everything else is the same. Basically, imagine Earth with half the gravity. I'm keeping the situation simple so I have a chance of understanding the core mathematics! :D
 

Eriseley

E
Un1k0rn said:
As said, only the gravity is different in my hypothetical'. Literally everything else is the same. Basically, imagine Earth with half the gravity. I'm keeping the situation simple so I have a chance of understanding the core mathematics! :D
Click to expand...

What he's getting at is this: gravity is determined by mass and distance. When you say "half the gravity", you could have Earth at exactly the same mass but but above it enough to experience half the gravity as on the land-surface. So Earth wouldn't have to change at all, just your location.

So for your interest, your question could kinda be reworded as: if you dropped the pebble at a height where G (gravity) is .5 of surface G on Earth, would it take 2 x time to land? Then you get a different answer. It's kinda your next step from a half-mass Earth with distances being the same!
 
Last edited:

gazelle

gazelle
Thargon said:
Time t taken for an object to fall distance d:
time = sqrt ( 2 x distance / acceleration due to gravity)
So yes, twice as long (plug in example numbers, compare).
Click to expand...

Aehem, NO! It takes sqrt(2) as long not twice as long. It will take twice as long if the gravity is a fourth.
 
Last edited:

phong

phong
THE GRAVITATIONAL MASS OF A BODY IS EQUAL TO IT'S INERTIAL MASS.In other words,the pebble has a gravitational field of its own which attracts the earth in ,as far as i understand it, equal proportion to their relative mass.
 

Patrick_68000

Patrick_68000
phong said:
THE GRAVITATIONAL MASS OF A BODY IS EQUAL TO IT'S INERTIAL MASS.In other words,the pebble has a gravitational field of its own which attracts the earth in ,as far as i understand it, equal proportion to their relative mass.
Click to expand...

So we have two magnets here
 
You must log in or register to reply here.
Back
Top Bottom