# Homework Help: Mass and weight differences on earth

1. Jan 21, 2004

### mmfoley

Hello,

How do the mass and weight of an object at the earth's center compare with their values at the earth's surface? My textbook is pretty terrible for the non-physics major. I think they answer this question in eqations rather than plain English, so I'm having a hard time with this. Basically, I'm trying to figure out if I dug a hole down to the center of the earth and dropped a rock down the hole, how would its mass and weight change from the surface of the earth to the center of the earth.

Thanks!!

mmfoley

2. Jan 21, 2004

Staff Emeritus
Well think about conservation of mass-energy. Has anything happened to change the mass? If it did, where did the compensating mass come from or go to?

As to the weight, well that's the force of the pull of the earth's gravity, right? How is the earth pulling at its center? Could you quantify that? Draw some diagrams.

3. Jan 21, 2004

### Tron3k

The mass will, of course, stay the same. The weight of an object at the Earth's center is zero.

4. Jan 21, 2004

### FZ+

Mass is a property of matter. It stays constant unless it is converted to or from energy.

Weight? Split the earth into a number of pieces. At the centre of the earth, gravitational attraction from each piece cancels out, as the ball is attracted from all directions.