Heavy Enough to Fall Through the Earth?

would a small object that is extremely heavy (about 500,000 tons or more) carve through the earth's crust if it was set down?
- Saroj (age 15)
United Kingdom

Hi Saroj,

Yes, it would.

The reason that objects don't fall to the center of the earth is that the force of gravity is balanced by the "normal force." Basically, this force arises because the forces between molecules in the ground are strong enough that molecular bonds aren't broken when we step on them. If the ground holds together, then we don't fall through.

If we step on water, the molecules aren't bound very tightly, and we fall right through the surface. Similarly, if we step on a shovel, the sharp edge is often enough to cut right through the surface of the ground. All that matters is how much pressure (force per area) the ground can withstand.

So, if you had a heavy enough or small enough object, it could cut straight through the earth. If the object was microscopic, it wouldn't have to be quite as massive. For large objects, the problem gets complicated, since the object would probably tear the earth up somewhat, as opposed to carving neatly through the crust.

I'm not exactly sure how to do any of these calculations, but I'd guess that any object that "only" weighed 500,000 tons would need to be very, very small.

However, there's a much easier way to carve through the earth's crust. Every day, billions of billions of particles (from the sun, outer space, etc) pass straight through the earth without noticing. This is because the particles don't interact strongly via the electromagnetic force, which makes up the normal force. If you don't see the normal force, then there is nothing to stop you from walking through walls, even planets, at will!

David Schmid

(published on 05/07/2013)