# Newtons forces confusion!

1. Jul 27, 2009

### dance_sg

1. The problem statement, all variables and given/known data

Newton showed that a centripetal force acts on an object moving in an orbit that varies

A. directly with the distance from the centre of force
B. inversely with the distance from the centre of force
C. directly with the square of the distance from the centre of force
D. inversely with the square of the distance form the centre of force

The question above is a question on the assignment that im trying to finish. However, i do not understand what the question is asking, or what he answers mean. What is the square? and how do i know if its inversely or directly? ah!! any suggestions??

2. Jul 27, 2009

### Feldoh

directly with the square of distance = distance^2

inversely with the square of distance = 1/(distance^2)

3. Jul 27, 2009

### dance_sg

ok. But how do i know if its inversly or directly? do i have to look at a formula?

4. Jul 27, 2009

### Feldoh

Well what's newtons law of gravity?

5. Jul 27, 2009

### cepheid

Staff Emeritus
You need to know HOW centripetal force varies with distance in order to answer the question (to pick the correct option). So yes, that would entail a formula for centripetal force that you ought to know.

EDIT: Okay, Feldoh interpreted "moving in an orbit" more narrowly that I did and assumed that the specific centripetal force in question was being caused by gravity. That could very well be what the question is asking about...

6. Jul 27, 2009

### dance_sg

so since r is the distance between the two point masses in the formula, then that means it would d, inversely with the square of distance. right?

7. Jul 27, 2009

### cepheid

Staff Emeritus