# Effect of changing gravity on flying animals

1. Mar 11, 2006

### Loren Booda

How would the ability to fly differ if the Earth's gravitational field were to change significantly?

Parameters of interest may include: weight, air density, air viscosity, climate change, evolution of flying creatures, comparison to sea creatures.

2. Mar 12, 2006

### Andrew Mason

Start with creature weight air pressure and density. How would they change if gravity increased or decreased signficantly?

AM

3. Mar 12, 2006

### DaveC426913

Why don't you offer us your thoughts so far, and we'll help you out.

4. Mar 12, 2006

### Cyrus

This question seems trivial to me. You can change the magnitude of gravity, but thats about it. Our abilitiy to model motion in gravity is due mainly to the fact that it is a (on the macroscale) uniform field that points towards the center of the earth. If you change this inherent property of gravity, none of the equations of motion apply, and you would have to perform some type of computer analysis to model each senario.

Your paramaters of interest are not in relation to gravity.

5. Mar 12, 2006

### lightgrav

Surely this context-rich open-ended scenario
isn't an introductory physics homework question!

Lift is obtained by momentum transfer rate to wing area.

We know that the atmospheric pressure is proportional to "g",
and proportional to the amount of gas (N molecules) in the atmosphere.
The amount of gas retained by Earth depends slightly on "g".

6. Mar 12, 2006

### Loren Booda

I was surprised (and disappointed) that my post was placed by the PF elite in "introductory" physics. I don't even know how to access that forum from the home page.

An increase in gravity should increase the absolute weight of objects, increase the density and viscosity of air. Think in terms of their effects on an airfoil.

Climate change, evolution of flying creatures, and comparison to sea creatures would be more long term subjects for speculation.

7. Mar 13, 2006

### cepheid

Staff Emeritus
Yeah, I don't think this is HW either. Looks like a nice discussion topic.

8. Mar 13, 2006

### FredGarvin

I think you would have to specify on what scale the change is. Are we talking a percentage or orders of magnitude change?

It's going to be tricky to deduce what the overall effect would be. Looking at things independent from each other:

Increased gravity = increased air density (lift improves)
Increased gravity = increased weight of object (lift degrades)
Increased gravity = increased air pressure (lift improves)
Increased gravity = increased air temperature (lift degrades)
Increased gravity = increased air viscocity (? I am siding with lift improves but that really depends)
Increased gravity = increased humidity (lift degrades)

I'm not quite sure where it would all come out in the wash. Good question.

9. Mar 13, 2006

### cronxeh

So say this was another Earth-like planet with an atmosphere of mix of oxygen and some other gas, and the mass of the planet was different, right? What is the n-dimensional formula for obtaining ideal conditions for life to be able to evolve on such a planet?

Lets say all variables were functions of gravity - atmosphere retention, chemical bounding, and an independent variable such as the type of available organic or otherwise matter (water, ammonia, acids, alkali, etc). Do we currently as humans have the capability to solve such question, drawing information from biology, physics, and chemistry?

I guess the next question and a more advanced one would be.. what is the range of possible evolutions such a creature may undergo?

10. Mar 14, 2006

### arildno

One might expect that a stronger gravity would increase the selection pressure towards light wings (porous bone structure, for example).

On Earth, a large glider bird like the albatross has extremely light wings relatively to wing length (the bone structure is very porous).
If the gravity becomes too strong, I'd assume large birds like the albatross will not be able to evolve.

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