Gravity and Density

[darth_timon]

Ok, my problem is this: I am currently embroiled in a debate about Star Trek vs Stargate, and currently my opponent is bringing up question marks around whether it's wise to assume certain planets are similar in size and composition to the earth.

Below is a quote from my opponent:

I will not limit myself to the use of my eyes to base a theory off of. You can in no way assume that the planet is Earth sized since one the actors would have to portray strain and ease accurately in all gravity situations to make an average comparison. Also there is a range of gravity that humans can appear to move around easily in even a difference of .5G can lead to a large difference in planet size. Furthermore you have no idea what the planets in question were composed of so you can at best only make a estimate of volume and not mass which is a much more important factor when trying to calculate gravitational force. This means overall that you can not estimate the size of the explosion relative to the planets accurately. Their yields are visually impressive but the look of the actual area after the fact is never seen. Also as I have stated before you can gear a nuclear device to release different kinds of energy, so a 20kt nuclear device geared for thermal release could look more impressive than a 1Mt nuclear device geared for neutron radiation so visuals can never alone make an accurate determining. Also again I will state that you do not know what form of energy a photon torpedo is geared to release neither are you capable of producing documentation detailing how a antimatter explosion should appear. Scientists follow the scientific method and would not base any argument or theory on a single source of ambiguous information like you have done with the events shown.

And another quote:

HAHAHAHA. Why would I have to provide evidence on something that you are using for the basis of your argument. You are basing your assumption on the planet being earth sized yet have no proof of such. So your argument is speculative at best because you have no comparative evidence. Im pretty sure you can disguise 2G while wearing a bulky space suit and walking. I myself have carried almost 1.5x, which is over 2G, my own body weight walking and looked fairly normal. I wouldn’t have been able to run normally because of where the weight was located and it restricting the freedom of movement but walking isn’t that difficult when the weight isn’t messing with your center of gravity. Also I am fairly fit and we are talking about trained military personnel and Teal'c so they should be able to make it look easier than I would. Rocky planets share similar composition but not the same amounts nor do they all have the same mass. Mars has 15% of the volume of Earth yet only has 10% of the mass. Which means that while composed of similar elements Earth is more dense which means has a higher relative gravity. This logical can be applied to all "rocky planets" and would give you varying mass, volume, density, and thus gravitational force. Again you have no evidence to support the size of the planet nor its mass so how can you even come to the conclusion that it is Earth sized when it could potentially be larger than earth but have lower gravity or smaller than earth and have higher.

Does he have a point, and if not, what's the best way to counter his claim?

[PeZook]

Pull out the equations for surface gravity ; Surface gravity is reliant both on mass and diameter. He's using vague bullshit, so pulling out the equation and running some simulations should lay that issue to rest.

For moement in high gravity: His example of how a man could move normally in 2g gravity is flawed, of course. Same vague bullshit: when he was carrying 1.5 his body mass (he said weight, though...heh ), his vascular system, breathing muscles, etc weren't affected at all. He should get on a centrifuge before claiming that running in 2g isn't a problem.

He does have a point about visuals of nuclear explosions, yes, but I take it you're estimating yield to within an order of magnitude? It shouldn't matter if your device releases, say, 15% of energy as neutrons instead of 5% in the megatonnage scales, the effects wouldn't be that different.

An antimatter explosion would look pretty much like a nuclear detonation, of course. The energy is released in similar forms in both cases.

You should be wary of arguing minutae, tough: identify the main thrust of the argument and tackle that. If you start arguing little points, you'll get bogged down.