Question: I'm trying to grasp the difference between *Kugel* and *Ball*.

So I took such spiky toy ball kugel thing:

[![spiky toy ball kugel thing](https://i.stack.imgur.com/4CAzl.jpg)](https://i.stack.imgur.com/4CAzl.jpg)

and went to ask a German person what that was. "It's a *Ball*", he said. "Because it's shaped like a *Kugel*, but a *Ball* is serving a greater purpose and is not about the geometric shape." (He really said that!)

So I asked him if a marble ball is more of a *Ball* than a *Kugel*.
This is what a marble balls looks like:

[![marble ball](https://i.stack.imgur.com/rmZyt.jpg)](https://i.stack.imgur.com/rmZyt.jpg)

He said, that's definitely more of a *Kugel* over a *Ball*. I asked him if marble balls had no greater purpose and he said he didn't know. :(

Well, now I'm super confused.

Somewhere I have read that every *Ball* is also a *Kugel*. And a *Ball* is made of flexible material. But that's not true in all cases, is it? I couldn't really find a satisfying answer to that on the Internet.

Answer: 
Kugel is the translation of sphere. And most of the objects you play with are called ball, e.g. Fussball, Handball etc.
I think it isn't that wrong to say that the hard materials like metal or glass are called Kugel and the softer ones ball. At least I can't think of any one that doesn't follow this rule.
I put the mathematical definition of *Kugel* aside. Others have elaborated on this quite enough. Instead, I focus on what makes a *Ball* (usually shaped like a *Kugel*) different to a *Kugel*. This can easily be answered by looking at various definitions of *Ball*.

Quoting [Wikipedia](https://de.wikipedia.org/wiki/Ball):

> 
> Ein Ball ist ein rundes, üblicherweise kugelförmiges, seltener ovales, elastisches Spielzeug oder Sportgerät aus Leder, Gummi oder Kunststoff.
> 
> 
> 

Quoting [Duden](http://www.duden.de/rechtschreibung/Ball_Sport_und_Spielgeraet):

> 
> kugelförmiger, gewöhnlich mit Luft gefüllter [elastischer] Gegenstand, der als Spielzeug oder Sportgerät verwendet wird
> 
> 
> 

First off, it may have a shape like a *Kugel* but this is not necessary; think of American football or Rugby. And it may be inflated with air.

But there are two main criteria which makes an object being called a *Ball* rather than a *Kugel*. The first criterion is that it's used as toy or for sports. This alone doesn't differentiate between *Ball* and *Kugel*, since some *Kugeln* are used for sports and games, too.  

The second criterion, however, is the key difference to *Kugeln*. *Bälle* are elastic. The degree of elasticity may vary. Some balls are still hard to form whatsoever, others break right away when you try to crush them. But they are elastic. This is not true for *Kugeln* (think of billiard balls, bowling balls, marble balls). Try to form them!