404. That’s an error.

The requested URL /custom?client=google-coop-np&cof=AH:left%3BS:http://physicslearning.colorado.edu%3BCX:Physics%2520Lecture%2520Demonstration%2520Websites%3BL:http://physicslearning.colorado.edu/images/ldlsmall02.gif%3BLH:47%3BLP:1%3BBGC:%23DAE0E5%3BT:%235F6A73%3BLC:%230568CD%3BGALT:%235F6A73%3BKMBGC:%23D0D1D4%3BKMBOC:%23D2D6DC%3BKMSC:%23333333%3BKMTC:%230066CC%3BKMTVC:%230066CC%3B&adkw=AELymgWC5Ar9E7r9yTBdSVFYjzFcHx-jcW-9CHxKbuSDpOsxEQpijO-tcbk99VDdhFcTl55V9wT59Q5cb_cT-zsznzVm40EiOzqoUMQNDw8Dk6kh60MKH3Y&boostcse=0&ie=UTF-8&oe=UTF-8&q=paddle+wheel+more:simulation&cx=013660194988778927211:7_tiwsj5d-c was not found on this server. That’s all we know.