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"  How big does a body of water have to be to have tides? &amp;quot;The answer depends on what you refer to as tides,&amp;quot; according to Todd Ehret, a physical oceanographer at the National Oceanic and Atmospheric Administration. &amp;quot;Most people think of tides as a periodic change in the surface level of a body of water, created by the gravitational force of the moon and the sun. But are you looking at theoretical differences or real and measurable differences?&amp;quot; How about Vince Vaughn&amp;#039;s bathtub? &amp;quot;The gravitational forces of the moon and sun are felt everywhere by everything. In theory, these forces can be felt in objects as small as a drop of water, but that tide would only exist at the subatomic level. For all practical purposes, it takes a very large body of liquid to have a tide. There is a tidal effect in the Great Lakes [of] less than one inch in height. They are considered nontidal.&amp;quot;  So, Oprah&amp;#039;s bathtub? &amp;quot;To have a true tidal effect \u2014 something that can be seen and measured \u2014 you need a body of water the size of an ocean or sea.&amp;quot;  Got a question? Send it to answerfella@esquire.com.  RELATED STORIES:  NARRATIVE: What It Feels Like... to Survive a Tsunami  FEATURE: How One Man Plans to Sail Around the World  PROFILE: Dean Kamen and His Magical Water Machine  INVENTIONS: Five Ways to Fix the Future of Water   ANSWER FELLA: Your Questions Answered   "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.esquire.com/news-politics/q-and-a/a5587/what-causes-tides-0309/>