The Dog with the Rope

A dog is tied to leash (rope) which is twenty feet in length yet is able to run to a bone lying fifty feet away.

The leash (rope) does not stretch or break in any way. Why?

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A dog is tied to leash (rope) which is twenty feet in length yet is able to run to a bone lying fifty feet away.

The leash (rope) does not stretch or break in any way. Why?