# Homework Help: Need help explaining this video

1. May 27, 2006

### Ukitake Jyuushirou

near the end of the video clip, the pilot does a "roll" and at the same time he is pouring water into a cup even though when he is now in an upside down position the water does not spill out of the cup, how is that possible?

Last edited by a moderator: Apr 22, 2017
2. May 27, 2006

### Andrew Mason

Last edited by a moderator: Apr 22, 2017
3. May 27, 2006

### Mattara

The spoilers are in the same color as the background.

Imagin that you are holding a piece of string with a cork attached to the other end. If you start to spin the string above your head you will that you must hold against to stop the cork from flying away. If you release the string the cork will indeed fly away in the direction of the tangent:

http://img236.imageshack.us/img236/9208/tangent3tz.png [Broken]

You need to use a force to stop the cork from flying away. This force is used to change the path of the cork so it moves in a cirular movement. This force is called centripetal force and is directed to the center.

The phenomena can also be observed in roller-costers. What makes a roller-coster continue without "falling off" in a loop?

The short answer is its speed.

The larger the speed the larger is the force that is directed to the center. If that force passes a certain magnitude the item will stay in its orbit.

You can verify this by yourself in a simple experiment. If you take a glass of water and turn it really quickly around, not fluid will be lost. Do it slower and all of the water will pour out.

Last edited by a moderator: May 2, 2017
4. May 27, 2006

### Ukitake Jyuushirou

is there a specific name for this effect?

5. May 27, 2006

### Hootenanny

Staff Emeritus
This is a simple application of circular motion, as the other posters have said you need only consider the forces acting to explain the effect.

~H