# Homework Help: Conservative forces

1. Aug 8, 2007

### livelife92

hiee...
ther r sum sentences in ma textbk dat i ve neva been able 2 understand..........

"a force is said to be conservative if wrk done by the force in a moving body depends only in the initial n final positions of the body during the motion":surprised
does it mean dat a force is conservative if wrk depends on displacement??????...bt thn why IS it said 2 b CONSERVATIVE??

""this is always true when any body is moved against the force of gravity ...weight is thus a CONSERVATIVE force""???!!!???

"KE and PE 2gthr make up the total mech E of an object'
...i knw dat....bt
'it remains constant if thr r no external forces 2 wrk on the body anddddd "THE INTERNAL FORCES ARE CONSERVATIVE""also thr shld be no sudden changes in the motion of d body:uhh:

plzzzz help me!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! i m jus nt been able 2 undrstand this.......the tchr. who teaches us phy. seems to mug up the text n throw up in frnt of us.......she is totally confused when i ask this.........
plz help me undrstnd this

2. Aug 8, 2007

### learningphysics

Friction is an example of a non-conservative force... If you take a block of wood on a table and move it from position A to position B... the work done by friction depends on the path taken... do you go in a straight line... do you go in a curve... the work done by friction will be different depending on the path taken...

But for gravity the path doesn't matter... just the initial and final heights.

When you have a conservative force, you can have a "potential" energy... like gravitational potential energy... elastic potential energy... electric potential energy they make things easier because you don't have to deal with those forces... just energies...

Last edited: Aug 9, 2007
3. Aug 9, 2007

### HallsofIvy

You seem to have a number of problems- extreme difficulty in writing a coherent sentence, for one, inability to understand that the "tutorial section" is not for questions- most people do not go to the tutorial section to answer questions!

I'm moving this to the homework thread where I hope you will get more responses.

4. Aug 14, 2007

### livelife92

ok sry...i wasnt careful while posting.....newayz..i needed an ans 2 my Q..

5. Aug 14, 2007

### CompuChip

ther r sum sentences in ur Q dat i cant undestnd eidr, prhps u cld try puttin in sum vowels 4 exmpl n use sum commas r dots r sumthn

No........ or yes!!!!!!!!!!!!!
It depends on the initial and final position, so the total displacement. It does not depend on the path taken. For example, gravitational force is conservative, because if I lift an object straight up by 1 meter, or I move it all over the world, to the center of the earth and finally hold it 1 meter higher than I started, in both cases the work done will be m g (assuming g to be constant). On the other hand, friction is non-conservative. If I move from A to B in a straight line, I will lose less energy in friction then when I move in a lot of tiny circles, for example.

Yeah, so actually PE is just a bookkeeping tool that allows us to (ab)use conservation of energy when conservative forces are at work.

6. Sep 17, 2007

thx!!