# Is it possible to use Newton's Law of Gravity AND Einstein's Theory of Gravity?

1. Oct 16, 2011

### studentxlol

Q) A mass of 100kg is 50m away from a mass of 250kg (from centre of masses). Calculate the gravitational force of attraction between both point masses.

Could I use Einstein's theory of gravity to answer this question using the information given. If so, how would I go about doing it?

2. Oct 16, 2011

### Pengwuino

Since Newton's gravity is just a low-energy limit of Einstein gravity, you technically are using Einstein gravity when you compute $F = {{GmM}\over{r^2}}$ :D

3. Oct 16, 2011

### studentxlol

Ok. Give me an example of a high-energy limit and what extra information I need to calculate using Einstein's formula.

4. Oct 16, 2011

### Jimmy Snyder

Einstein's equations don't calculate force. They describe the shape of space-time. Objects move along geodesics of the space-time. No force.

5. Oct 16, 2011

### khemist

So you would actually have to calculate the curvature felt by each object, which would be a kind of sum of the distortions from each mass?

6. Oct 17, 2011

### Jimmy Snyder

Yes. Probably the easiest calculation is the bending of light as it grazes the sun. There is an excellent book about this and very easy to read. "The Einstein theory of Relativity" by Lieber and Lieber.