text: "A scientific law is like a slingshot. A slingshot has but one moving part--the rubber band. If you put a rock in it and draw it back, the rock will fly out at a predictable speed, depending upon the distance the band is drawn back. \n\nAn automobile has many moving parts, all working in unison to perform the chore of transporting someone from one point to another point. An automobile is a complex piece of machinery. Sometimes, improvements are made to one or more component parts. A new set of spark plugs that are composed of a better alloy that can withstand heat better, for example, might replace the existing set. But the function of the automobile as a whole remains unchanged. \n\nA theory is like the automobile. Components of it can be changed or improved upon, without changing the overall truth of the theory as a whole."\n\nFrom: http://wilstar.com/theories.htm\nThat analogy helps explain the difference, for direct definitions of scientific theories and laws see the link provided.