An example of a teaching analogy:
"A catalyst is a substance which stimulates or causes a chemical reaction to take place, but is not itself permanently changed as a result of the reaction. A catalyst is like a minister at a wedding ceremony…the minister causes the ceremony to take place, plays a role in determining how fast the ceremony takes place, and is not himself [or herself] permanently changed as a result of the ceremony…unlike the couple getting married, who are permanently changed as a result of the ceremony!"
Source: Murray Hart, retired science teacher, previously posted at scienceanalogies.com
Read examples of scientific analogies
Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.