Wolfram Alpha does unit conversions just as well as Google, but it lets you dig much deeper. For instance, try a search along the lines of “20 miles + 24 kilometers” to get the answer in miles, kilometers, centimeters, nautical miles, and even how that distance compares to a marathon race or a Formula One track lap.
Physics queries are well-handled, too, including those involving thermodynamics, mechanical work, gravitational calculations, magnetism, optics, relativity, and centripetal acceleration. Just plug in the formula you want resolved and let Wolfram Alpha work its magic.
If chemistry is your field of interest, the search engine covers elements, compounds, ions, chemical quantities, and more. A query such as “12 pounds of 4-cyanoindole” returns a long list of information that includes mass composition, a structural diagram, the chemical name and formula, and even its melting point.