What is density? The definition of density is ñ = m/V, where m is the mass, and V the volume.

 

“How do we measure volume V?”

 

“Length times width times height”

 

“Correct. This is one way. We take a ruler and measure the object.” Note that we must stress the ruler, and not merely use the memorized formula l×w×h.

 

“Another way is to use a bottle with volume marks on the side.” I carry around water bottles, and show them the volume markers.

 

Show the class two bottles, one full of water, and the other empty. The volumes of the bottles are the same. The empty bottle has a smaller density. This way they get a feel for the concept of density. The important thing is not to think of density simply as mass divided by volume, but to think of density as a concept in its own right.

 

Look at the empty bottle. The density is less than the same volume of water. The bottle will float. How do steel ships float? Because the density is less than water!

 

By the way, we should not get confused with a needle floating.

 

SEE THE BOOK FOR MORE DETAILS.