Answer:
<h2>Gravitational Force.</h2>
Explanation:
While Steve is whirling a rubber cork, it developes a situation which is similar to the Solar System. In the rubber cork movement, there's "circular" motion which is possible thanks to the string, that is, the string works as "attraction force", allowing the system to maintain its movement.
Now, in the Solar System, the graviational force is like the string, it's the physical magnitude that maintains planets on their movements, attached to the Sun someway.