# A Comic Question

1. Oct 15, 2005

### randy23

I'm a comic fan especially Superman and one of his feats dealt with him holding the moon that was supposedly increasing in momentum at fraction of a G-Force. My question is: is that really an impressive feat? A fraction of a G-Force? If it was half of a G-Force, how much force would he holding back against the moon to keep it stationary?

2. Oct 15, 2005

### JesseM

The question isn't too clear, momentum isn't measured in units of force or acceleration...are you saying that if Superman wasn't pushing back, the moon would be accelerating at 0.5G? Because the moon is so massive, the force needed to get it to accelerate like that would be pretty huge (just multiply the moon's mass by an accelation of 0.5G), and the force needed to push back and prevent the moon from accelerating would need to be the same size.

3. Oct 15, 2005

### randy23

Well I'm not sure about the momentum. DC is pretty much based on pseudo-science but I just wanted to know using real sciences. Thank you for the insightful reply.

4. Oct 16, 2005

### Janus

Staff Emeritus
For some numbers, the amount of force needed to accelerate the Moon at .5g would be about the same as what it would take to hold up a 80,000,000,000,000,000,000,000 lb weight on the surface of the Earth.

5. Oct 16, 2005

### randy23

Janus, thanks for the calculations. How did you go about calculating that number?

6. Oct 16, 2005

### Janus

Staff Emeritus
The Moon has A mass of 7.35 x 1022 Kilograms
A mass of one kilogram weighs 2.2 lbs on the surface of the Earth at 1g.
The same kilogram would weigh half as much at 0.5g or 1.1lb.
1.1lb/kg x 7.35 x 1022 kg = 8 x 1022lbs

7. Oct 18, 2005

### randy23

Thanks. But the fraction of g-force they commented about could also mean .000000001, right?

8. Oct 18, 2005

### Janus

Staff Emeritus
Okay, then the weight would be 160,000,000,000,000 lbs. (about equal to the weight of 10 billion African Bull elephants)

9. Oct 19, 2005

### tony873004

Why would Superman want to tinker with the Moon? It's fine where it is.
If Superman were pushing hard enough on the Moon for it to have any significant impact, he would probably push through the Moon instead. If 10 billion African Bull elephants had their mass compacted into the size of Superman I doubt the surface of the Moon could support it. Superman would quickly find himself at the core of the Moon. But that would be cool because he could tell us what it is made of. I know the surface is Swiss, but I believe scientists theorize that the core is Cheddar.