# Homework Help: Conservative force

1. Dec 6, 2006

### m2287

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

If a force on an object is always directed along a line from the object to a given point, and the magnitude of the force depends only on the distance of the object from the point, the force is said to be a central force. Show that any central force is a conservative force.

2. Relevant equations

3. The attempt at a solution

i really dont have a clue....

im guessing work done = force * distance

and F = ma might be used but i dont know how!

2. Dec 6, 2006

### Hootenanny

Staff Emeritus
What is the definition of a conservative force?

3. Dec 6, 2006

### m2287

that if you move an object around and place it back in its original position no energy is lost?

4. Dec 6, 2006

### Hootenanny

Staff Emeritus
Correct. Can you therefore write an expression for the work done by a central force?

5. Dec 6, 2006

### m2287

wd= ma * d ???

6. Dec 6, 2006

### Hootenanny

Staff Emeritus
Close but don't forget that the magnitude of the force is dependant on the displacement. Use vector notation for the displacement and write ma as F.

7. Dec 6, 2006

### m2287

does than not just give you wd = f* d

im very confused about how to prove this!

8. Dec 6, 2006

### Hootenanny

Staff Emeritus
No. Note that the magnitude of the force is a function of displacement and note that we are looking at displacement which is a vector quantity. Now, because the force is not constant (because is varies with displacement), we cannot use the simple relationship you outlined above. Do you know a general definition of the work done by a force (involving calculus)?