Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: A weighty question

Learn more physics!

Most recent answer: 10/22/2007
Q:
Can the Earth ever become too heavy from manmade objects, like large cities? Could we ever build anything that would affect the weight to the point of the Earth falling out of rotation?
- Shari Stuart (age 16)
Cary High, Cary, NC
A:
Nope, there is (almost) nothing we can do to make the Earth heavier! All the manmade objects actually consist of raw materials which come from somewhere on or in the Earth to begin with. All we can do is rearrange the atoms we find around ourselves.

That having been said, there are some very, very tiny exceptions to this rule. We have brought rocks back from the moon, and may someday bring some back from Mars, who knows? Many many more rocks fall on the Earth of their own accord, though (meteors and meteorites. Even if a meteor burns up in the sky as it falls in, its atoms are included in the Earth's total mass -- the ashes fall down). Models of the formation of the Earth in the first place usually involve many collisions of small objects sticking together.

The net effect of the space program, I am afraid, is to reduce the total weight of the Earth, as we have sent spacecraft out there we do not expect to ever get back.

I don't think we can affect the orbit of the Earth significantly by sending spacecraft out. One concern, though, is that a big asteroid may collide with the Earth, causing a lot of damage. I'd imagine the damage (floods, earthquakes, etc) would be of concern starting with much smaller asteroid impacts than ones that would noticeably affect the Earth's orbit. In short, if something happened to change the Earth's orbit, we'd probably have worse problems to worry about.

Tom

(published on 10/22/2007)

Follow-up on this answer.