# Physics experiment help

1. Feb 21, 2010

### ahhppull

1. The problem statement, all variables and given/known data
I have to explain an experiment. The experiment can be found here: http://phun.physics.virginia.edu/demos/tray.html

2. Relevant equations
None

3. The attempt at a solution
I checked the website above, and I don't quite understand it.

2. Feb 21, 2010

### Delphi51

You need to make some sort of attempt before help is given in this forum.
In this case the answer appears to be given in the link - just scroll down a bit. Don't hesitate to ask about any part of the explanation that you have trouble with!

3. Feb 21, 2010

### ahhppull

Well, I don't know what the equation for centrifugal force is...i tried looking it up.

Also I don't understand what the difference between centrifugal and centripetal force is.

4. Feb 21, 2010

### ahhppull

On the website's explanation, it says "The water does not fall, however, because it is experiencing an upward force due to its circular motion. This force is great enough to cancel out the force due to gravity.".

Which is the upward force? Centripetal force or centrifugal force??

5. Feb 21, 2010

### Delphi51

Centrifugal vs centripetal is certainly confusing!
You have one OR the other depending on how you look at the situation.
If you look from the point of view of the object in circular motion, you have centrifugal force - outward. If you look from the point of view of the outside world (not in circular motion) there is centripetal force inward toward the center, holding the object in its circular path. The two forces are both equal to mv²/R.

I suggest you take the point of view of the water, moving in circular motion, so you have centrifugal force away from the center. When the pail is at the bottom of its path, the force is downward and it just adds to the gravity force to hold the water more strongly inside the pail. At the top of the path, the centrifugal force is upward. If it is at least as strong as gravity (pulling down), it will hold the water in the upside down pail.