As different JS Frameworks use the $ for it’s functions (jQuery, MooTools), WordPress loads jQuery in the “noConflict”-Mode, which means that it doesn’t use the $ but only jQuery.
You can now
- use jQuery instead of $
- encapsule your calls like RiddleMeThis proposed
On a personal note: honestly, it’s not that big a deal to replace the $ with jQuery, isn’t it? 😉
Happy Coding!