# Balls puzzle.

1. Aug 10, 2008

### Sakha

You have 2 balls. Both are identical in size and mass, but one is made of gold and is hollow,the other is not hollow and made from titanium. Find out which is which ball, and lets say both are covered with a black paint that is anti reflective, heat/electricity insulator. You can't use any measurement device, nor hitting, damaging or breaking the ball..

P.S: There's a really simple way.

2. Aug 10, 2008

### DaveC426913

Knock them? One will sound hollow?

3. Aug 10, 2008

### Sakha

Mmm.. lets say the paint is anti-acoustics.

4. Aug 10, 2008

### lisab

Staff Emeritus
Roll the balls side-by-side down a ramp. The solid ball will roll faster.

5. Aug 10, 2008

### Sakha

wheew.. you're fast..

6. Aug 10, 2008

### DaveC426913

Around here, we like our women that way.

7. Aug 11, 2008

### regor60

drop them in water. the hollow one will bob higher.

oh..same mass, never mind

8. Aug 11, 2008

### Sakha

Nice try.

9. Aug 11, 2008

### arildno

Remove the paint?
(This as an alternative to lisab's suggestion)

10. Aug 11, 2008

### some_one

oohh rigid bodies thats realy good

11. Aug 11, 2008

### some_one

put them in a bucket of water
they vary in density
the gold will pull out more water
am i correct?

12. Aug 11, 2008

### Sakha

As I said, you can't damage nor break the ball, and removing the paint would be considered damaging. But yeah, lisab's answer is right.
Both would pull same amount of water because both are same size and mass, so they have same volume and density.

13. Aug 11, 2008

### arildno

I think black is a damaging colour, I'm merely prettifying the balls..

14. Aug 11, 2008

### some_one

aaahhh disregard it
you sayed that the gold ball is hollow

15. Aug 11, 2008

### Sakha

No, imagine a gold sphere as an "o" the black line is gold and the white is hollow... The titanium sphere is all solid.

16. Aug 11, 2008

### some_one

if you shoot them out of a cannon
the gold ball will not fly in a steady trajectory
because its hollow

in order to fly in a steady way you need to have a full ball

because from my knowledge
the AK bullets have a shifted center of mass
which make them highly unstable
and when they hit a person
they are starting to swirl inside the victim

am i correct?

17. Aug 11, 2008

### arildno

The middle of the gold ball is empty, some one, it is hollow.

The hollowed gold ball can perfectly well have the same size and mass as the compact titanium ball

18. Aug 11, 2008

### Sakha

Actually I don't know. I didn't went that far.

19. Aug 11, 2008

### LowlyPion

Titanium is paramagnetic.

20. Aug 11, 2008

### some_one

i am not a physicist but i had some small experience with fire arms

and i know for a fact that bullets with a shifted center of mass
are swirling inside the victim instead of going threw him

the question is whether the hollow ball considered to have a shifted center of mass