When I search on Google for "unit of impulse", it returns Newton, which is unit of force. Does anyone know why that happens?
That happens because Google is not perfect. Please click on the "Send feedback" shown below the knownledge panel and send your feedback to Google.
The following screen shot was taken from the results page for your link shown to me. It shows a knowledge panel having as title Newton but the summary snippet was taken from the Impulse (physics) article from Wikipedia. It shows the word "newton" in bold as it was a term when in this case the term is newton second
Some how the relationship between the term Newton and the Wikipedias article for Impulse was not correctly presented in the results page.