# Why does water or balls spill out ?

1. Dec 30, 2015

### Sunanda Goh

I know, this is a very stupid question, but it troubles me the whole day and i can't figure it out.
Why can't water remains its shape if the cup is being removed and the water will spill all over the table ?
And if you fill your car with full of small balls and when you open the door of your car, the balls spill out too ?
Is it Gravity or ? But isn't gravity a downward force ?
Forgive me stupidity

2. Dec 30, 2015

### Bystander

There is a "tendency" for net reduction of potential energy (height above ground level).

3. Dec 30, 2015

### SteamKing

Staff Emeritus
What's the matter with gravity being a downward force? Do the balls spill out of your car in an upward direction when you open the door?

4. Dec 30, 2015

### Sunanda Goh

Nope. That's why I'm asking if it's Gravity.

5. Dec 30, 2015

### Staff: Mentor

6. Dec 30, 2015

### DaveC426913

https://en.wikipedia.org/wiki/Angle_of_repose

Every material has its distinct angle of repose - as any sand castle builder knows.
I encountered this yesterday, while trying to dig down into the blown cellulose insulation in my attic.

Water has an AR of 0. :)
Round balls would have a variable AR, depending on how orderly-stacked they might be.

7. Dec 30, 2015

### Sunanda Goh

Woah ! Thanks !

8. Dec 30, 2015

### Svein

Or you could just say Entropy - the universe tends towards equilibrium in all things.