# Why doesent water fall down from a bucket while rotating it upside down?

1. Dec 13, 2005

### chound

Why doesn't water fall down from a bucket while rotating it upside down?
Also:
1)What causes sound when bombs explode? Is it the quick heating of air and compression something like sonic boom
2)How do the ariel fireworks go up and explode?

Last edited: Dec 13, 2005
2. Dec 13, 2005

### rbj

don't wanna deal with 1 and 2, but the answer to question 0 is that the premise of the question is wrong. water does fall from the bucket if the rotation is slow enough.

if the rotation is so fast that the bucket is accelerating downward faster than the acceleration of gravity, then the bucket is forcing the water to fall faster than gravity and since the sides and "bottom" of the bucket are pushing the water to accelerate faster than gravity is pulling (out of the open "top" of the bucket), the water does not escape the containment of the bucket.

3. Dec 14, 2005

### chound

rbj Can it be expressed mathematically as Weight = mass(gravity-acceleration of bucket),
since a >g it experiences negative weight?

4. Dec 14, 2005

### Danger

I'll take #3. Commercial fireworks are launched by computer control (although some artists still sequence them manually) from a series of mortars. The launching charge determines how high they go, and an internal fuse that is lit during launch determines at what time they explode. Any secondary explosions are fuse-timed from the bursting charge. It's actually a very intricate system.

5. Dec 14, 2005

### Astronuc

Staff Emeritus
As for 1. this is an effect of centrifugal force - http://hyperphysics.phy-astr.gsu.edu/hbase/corf.html#cent

In general - http://hyperphysics.phy-astr.gsu.edu/hbase/circ.html

It is important to understand the difference between centrifugal and centripetal forces.

#2 - Sonic booms arise from the compression of air on the leading points of an aircraft which reaches, then slightly exceeds the speed of sound in the air.

This might help - http://en.wikipedia.org/wiki/Sonic_boom

#3 - Aerial fireworks are launched from a mortar (usually steel metal tube). There is a launching charge, which propels the pyrotechnic charge into the air, and the burst charge inside the package.
http://people.howstuffworks.com/fireworks2.htm

6. Dec 14, 2005

### Dmstifik8ion

Momentum (motion) applied to the bucket is imparted (delivered) to its contents, the water inside. Once the water is in motion it has a tendency to continue its motion at the same speed and direction (velocity), in a strait line. Once sufficient motion is reached this tendency (inertia) overcomes the pull of gravity and the water remains inside.

7. Dec 14, 2005

### Staff: Mentor

Another way of saying what rbj already explained: Since the bucket of water is being whirled in a circle, its acceleration is centripetal. At the apex of its motion that centripetal acceleration is downward. If the bucket is moving too slowly, the centripetal acceleration will be less than g and the water will begin to fall from the bucket; but if the speed is sufficient to make the centripetal acceleration greater than g, the water will be pressed into the bucket and will not spill.