Do this activity as a hands-on, but with careful supervision. You will need something to boil water in, a box of salt, 2 one quart sized containers, plain water and two or three eggs, uncooked but in the shells. Boil about two quarts of water, adding as much salt as can be added and still dissolve. Let this cool, then fill two quart containers, one with the salted water, one with plain water. Have children carefully place one egg in each container. Which one floats? Explain the differences in density of the water solutions. Salt water has more density than fresh water because it has more mass.
Gather four clear glasses, clear straws, clay, an ordinary dropper, salt, alcohol, water, glycerin, a measuring cup and different food colorings. Fill each separate glass as follows: one with one fourth cup of water, one with one fourth cup alcohol, one with one fourth cup glycerin and one with one fourth cup salt water. Add different colors of food coloring to each glass. Have students anchor a straw in a small lump of clay to enable it to stand upright on a table. Instruct students to add, by dropper full, a bit of each of the contents of the four glasses into the open end of their straw. The clay holding the straw will not allow liquid to go all the way through. Note, with the students, the layered affect the liquids have as they are added to the straws. Explain to students that the cause of the layers is the difference in density, or mass, of each liquid.
Create a lava lamp out of water, oil and salt. Instruct students to fill a clear glass about three fourths full with cold water. Add regular cooking oil to each glass until an inch or so of oil is on the top, explaining the difference in density between the two liquids. Sprinkle some salt, which has a greater density than both liquids, on top of the oil and view the results. The oil, having a texture that adheres to the salt for a while, makes the oil move with the salt through the entire mixture. Show students that as the oil gets released from the salt, it will naturally move upward once again producing the "lava lamp" scenario. Add food coloring to oil to make the "lava lamp" even more interesting.
Instructing students that many objects, not just liquids, have different densities begins this activity. Fill a glass with honey, regular cooking oil and water in equal amounts but in that order. Allow the liquids to settle. Ask the class what they think will happen when you drop a cork, a penny and a grape into the mixture. Write their answers on the board. Drop each item into the glass and record where the items remain in the glass. Note the layers of floating objects to the students and explain the differences in densities, not only of the liquids, but of the items floating. Use many different types of objects and liquid solutions to redo this activity as many times as desired.